Great video!! Here's my theory. When the clamps were removed after 30 minutes, the glue hadn't cured enough to compensate for the release of pressure. The boards pulled apart just a little bit on their own and messed up the glue. When you just pushed the boards together and left them, there was no change after 30 minutes, so the joint was stronger. Maybe?
Agreed, to look at it another way, the clamps squeeze out far more glue than the "hand pressed" version, so when the pressure relaxes to "clampless", there is less glue in the joint than the hand pressed version, but a wider gap than the long-term clamped version.
I was a research engineer for 10 years designing and carrying out experiments, and a woodworker since before that. This is one of the most complete and robust scientific woodworking experiment videos I've seen. Controlling for all sorts of variables via sensors that most others would ignore. Thank you for this video, I and countless others will benefit from your rigor! I'm about to glue up a large table in half a dozen glue ups and this will save me days!!
Thanks dude! I could have added more variables like letting each of the conditions dry 24hrs but it takes so much material and time to do this experiment as-is. I’m glad you appreciate the consideration that went into the setup.
@@WoodcraftBySuman There are always more variables! You seem proficient at identifying and appropriately accounting for the important ones to reach practical, useful conslusions which is what makes good science. Most videos like yours are woodworkers taking a stab at being scientists, with varying success. You strike me as a scientist first, applying yourself to woodworking. Do you have a background in research?
@@WoodcraftBySuman Not a lot of fields that have a future in research beyond academia, biologics seems like it would be a good one. I worked in metal product manufacturing research and applications. Very large lab with lots of fabrication, inspection and data collection equipment - lots of work with load cells, they are so incredibly valuable for experiments but unfortunately very expensive! Stuff I've always dreamed of applying to woodworking so your videos resonate strongly with me, I'll be binging them over the next few days.
@@FlyingMoose_ that’s super cool! And hope you like the videos. I only have a few on testing stuff as this has been a recent pivot for the channel. I will continue to make testing or testing adjacent videos going forward.
I worked in a furniture mill in the early 1980's. When making raised panel doors with standard stick and cope construction, our rule was to leave the doors in the clamps for at least 2 hours. After that time, they could be removed from the clamps and stacked if we needed the clamps for another batch of doors. (We typically made doors in batches of 50 to 100 doors.) We were using a typical PVA glue, something similar to Titebond Original, which we bought in 55 gallon drums. We let the doors cure for approximately 24 hours before doing any additional work on the doors (trimming to final width and length, putting an edge profile on them, sanding, etc.). I follow the same practice in my shop today. I leave a glue-up in the clamps for at least 2 hours and don't stress the joints for about 24 hours. I've never had a glue joint fail when following these procedures. (Except for the time at the Furniture Mill when someone stored a 55 gallon drum of glue outside, overnight, in sub-zero temps. None of the joints made with that glue held! PVA glue is ruined by freezing.)
Ruined by freezing, eh? Guess I should be throwing away all the bottles that sat in the garage over the winter and experienced repeated freeze thaw cycles. Not a lot of glue, but a couple of small bottles from when I couldn't find the last one and just bought new.
No. We confirmed with our supplier that freezing ruins PVA glue. If your glue freezes, simply throw it away. There’s nothing that can be done to make it work after that.
I can attest that frozen wood glue does not work that well after thawing. I’ve also accidentally let CA glue freeze and that stuff is worthless after that
Great info. I think one important point was unstated or understated: the piece without clamps was not disturbed. We saw how little force was required to break the joints when the glue had not dried yet. Clamps hold the pieces together so that they don't come apart from something as minor as bumping the table that the glued pieces are on. Edit after watching again: the proper testing would have been to clamp for 1, 4, and 12 hours - then waiting to test until the glue had cured at 24 hours. While 30 minutes was shown to be too little, it was not shown what happens at 1, 4, or 12 hours. The assumption that 4 hours is enough is merely assumed.
I agree with you that a second subset of 1hr, 4hr, and 12 hr clamp time with full 24hr cure would have added better data for consideration on this video. Two reasons why I did not do that: 1) it makes the video longer and slightly more complicated to follow. I have to consider average view duration and retention times when making videos on youtube. 2) it would take a lot more wood and I felt bad wasting so much wood as-is. Because 4hrs is able to get strength that competes with the strength of the fibers itself, it is a reasonable conclusion to make that 4hr clamp time generates strong enough joint to remove clamps at room temps and 200psi. Tests like this are just that: tests. How I chose to break the joints is not necessarily analogous real world conditions. Some people glue up in 65F shops and others in 85F shops -- this will have a huge impact on clamp time needs. There are certainly other ways to test this topic and I may even explore it in future videos. Thanks for watching.
Jupp, this is how it should haven been tested. No need to leave a glue up for 12-24hours in the clamps. Clamp for 2-4 hours and let the glue dry for 24 hours before applying thr full expected load. Assembly can continue after the 2-4 hours, if you don't stress the glue line to much.
@@WoodcraftBySuman I can see that work and time and material has to be finite and you have to stop at some point. However your argument about "viewer retention" is unfortunate. Good methodology is like good workmanship quality: A bit of a pain to follow through with, but viewer retention through reputation is worth much more IMO. Compare for example to "Project Farm" testing. Always super meticulous. And look where it got him! (Just speak faster and edit more? 😁)
As a mechanical engineer I applaud your approach and execution. As a long time wood worker I just found the answer to a question I have wondered about for 50 years. Congratulation, Suman, you deserve a big thanks.
My rule of thumb from a practical and time efficient standpoint was to clamp up in the evening and let dry overnight then release and carry on the next morning. Has worked for me for decades.
Testing that actually uses multiple samples and throws out the top and bottom? Here on TH-cam? Amazing! Seriously, I find it so refreshing to see a real effort to apply the scientific method. Thank you! (I've wanted countless woodworking videos here, but this is the first of yours. I subscribed.)
That is a pretty common approach to doing simple statistics. The idea behind throwing out the extremes is to remove the cases where something unusual happened, letting you focus in on the most common examples. When I googled it I mostly got examples of how to do it using tools used for such analysis (Excel spreadsheets, MATLAB) rather than WHY. Which supports the idea that it is common, since so many questions about how to automate it have been asked.
@@somebodypeculiar Thanks for looking into it! That's also what I found. I was hoping there was some statistical rule of thumb that outlined the why. To me, it seems like just lopping off the top and bottom gives an artificially high confidence in your data's consistency. I'm not good at statistics though, so that's why I ask.
Actually, removing the extremes is often a sign of a lack of confidence in the quality of the data. Measurements that are way off from the rest can be the result of a bad measurement. Or they can represent failure of an experimenter to repeat the process consistently. It is a rough-and-ready approach to trying to reach a good rule-of-thumb, rather than a rigorous statistical process. For that matter, the average (mean) isn't always the best measure to use; the median is often preferred, where half the samples are above that point and half below. Note that while the drop-on-from-each-end approach can change the average, it can not change the median.
@@somebodypeculiar So it's like a quick and dirty way to try to limit the influence of outliers without having to actually know how to identify true outliers. I think I understand why people use it better now, thank you.
I'm glad that I can safely free up my clamps in shorter intervals, since I started woodworking I'd usually leave glue-ups for 8 hours. Great video! The pacing of information throughout was perfect.
For the 30 min clamp 24h dry --> The wood changed shape after unclamping, but the bond was not compete. The wood applied a separating force that the glue could not expand to fill. This is partially driven by the moisture from the glue entering the wood.
I second this nomination. I've always wondered that myself. But like Suman says, Im putting possibly too much glue, and relying my choking of my clamp handles to squeeze out what it doesnt need. I'm a drowner, but have found the only downside of this is cleanup time, and using more glue. But I'm a weirdo, and enjoy the glue scraping/cleaning process....its cathartic.
As a non-woodworker who frequently puts bits of wood together, I'd also like to hear/see the results of flood v's sparing. As well as that, what about the effect of lightly moistening the joint face with water (to open the pores) before applying the glue?
This is a super helpful video ! I didn't realize how much risk I was taking unclamping my glue ups at 30 minutes. You've probably saved many people at least one project disaster. Very through analysis !
I am so glad you did the hand test, because I cannot tell you how many times people have told me 'you should clamp that'. I usually just use tape on veneer repairs (small pieces) unless it may shift. Its always been fine. Thanks for the video!
Great vid, I’m sure this will be very useful and informative to a lot of people including myself! My totally unscientific thought on the 30 min/24 hour surprise breakage is that maybe it could be that when the pressure is released before the glue is fully cured, the wood slightly ‘rebounds’ when the clamp is removed and causes a sudden shift in force that might upset the bond, whereas an even pressure scheme for the entire cure time wouldn’t experience such disturbance in the forces and glue line. Just a thought for future vids - it would be nice to have a text layover of the test conditions (clamp time etc) during the part of the video where the breakages occur in the testing. Good for easily distracted people like myself to see where we’re at. Keep up the great work, I love this channel!
Excellent video! Two thoughts of mine you didn't ask for 😬 : - It would be helpful to see how all those clamping times fared with the recommended 24-hour unstressed period after removal from clamps (or perhaps a period that would add up with clamping time to 24 hours total to keep all the samples identical in total cure time). If the full day of curing took the 30 minute clamped batch halfway to the strength of the 24 hour clamped group, I'd be fascinated to see how, say, the 1 hour or 4 hour group would fare after the full 24 hours. Either case would still free up clamps much sooner then the common "clamp for a day" thing a lot of us do. -The hand-clamped results are fascinating! I'd love a comparison between those where you just pushed them together to a sample group you joined with rub joints. Would the atmosphere offer greater pressure in that regard? Would the joint be any noticably different from your first group? Again, amazing work, man! You more than earned this sub.
Love how thorough you were with this. You have saved me from the worry of "Have I clamped this long enough" I was at overkill with overnight glue-ups lol. Thanks Suman.
Wow! No fluff, only the good stuff. Literally packed a 30 minute video into 10 minutes. Played at 1.5x that's less than 7 minutes! You won't find a video packed with more info per minute. Took me longer to write this comment than watch the vid - very well deserved. How could I not subscribe? Genius! Thank you man - been prayin for vids like this!
I'm a cabinetmaker. When I was an apprentice, and going to trade school, I was taught that a properly glued joint (not too much glue, not too little) needs to be in the clamps for at least 10 minutes. And properly clamped of course. So not too much force, where you're squeezing all the glue out, and not too little force, where it's not even doing anything. In practice, I like to keep clamps on at least one hour. If it's something big and complicated, I leave it overnight. It's also important to note that regular white PVA glue is perfectly strong enough to use for furniture, as long as the joints are put together as I've described. Yellow glue, or "carpenter's" glue, also known as aliphatic resin, is typically a stronger adhesive, as it's meant for structural purposes. Titebond III is an exterior PVA, but I've noticed it is thinner and runnier than regular PVA, and it definitely needs more than 10 minutes in clamps.
I have a video suggestion for your test rig. It would be cool to see testing done to compare fluted dowels, spiral dowels, regular dowels, and maybe miller dowels too for the fun of it. I'm curious if the friction of a regular dowel causes glue starvation, or if the different types of dowels cause any significant difference in strength in the joint. I've never seen anyone test this before and many woodworkers use dowels in their joinery.
Love the process you used, I'm 60+ years old and spent my life thus far as an engineer asking the questions you asked. Well done! About to retire and spending more time in the wood shop, been thinking about my glue ups, hum... and you just did 700% of the work. Thank you so much. Youre awesome, thank you. Honestly, I think you out engineered Tightbond on their instructions, and you were very graceful, well done.
As an owner of a WW business, (and an even smaller YT channel than yours...lol) this is very helpful information. I got into the habit of writing the time on my glue-ups and waiting about 3 to 4 hours with only enough clamping pressure to get squeeze-out along the entire edge. As to the LAST TEST...my theory would be that the initial pressure squeezed out most of the glue and then releasing that intense pressure left the joint a little "glue-starved" for final curing.
This males perfect sense. there may even have been air ingress once the pressure was removed from the glue starved joint. I'd love to see a magnified shot of the break
As an engineer myself I have to say: Perfect execution! 🤩I love how you put attention to all the details! And the results are also very helpfull ... thanx for investing your time. 👍
This is an excellent video on glue ups. I usually wait at least 1 hour before handling or working with glued material on fast moving projects, but now will wait longer after seeing you video. Thanks a million
my hypothesis on the 30m clamp 24hr dry boards is that the clamps force much of the glue out, but the bond after 30m isn't enough to the adherants to maintain the joint and so it weakens. i've had this type of result when overclamping joints, wiping up the squeeze out and then backing off some of the pressure. i had a tabletop split right down the glueline this way and ended up doing some testing to figure out why it might have happened. i found it was pretty well understood that too much pressure can starve a joint and i suspect that backing off the pressure after clamping is creating a similar situation.
Love the evidence-based approach to woodworking, Suman. Could you put error bars on your averages in future? It's important to see how much variation is caused by the test variable relative to uncontrolled variables.
By clamping you push excess glue from joint. When you remove clamps after 30 minutes you release pressure on wood so a little tiny gap can occur on joint, but there is no glue to fill that gap. So it doesn't matter that you leave it for 24 hours, joint is already weak. When you making joints using just hands or weak pressure, you don't push so much glue out from joint, you don't store tension in wood, so wood don't try to break that joint and glue can do the job. There is probably a little more glue in such joint but it doesn't matter.
Congratulations on your very carefully controlled methodology, I hate testing videos that don't even care to make sure the samples and force applied are as equal as possible, it made me really happy to see all the care you put into this, it doesn't go unnoticed.
I like this video very much because as an engineer, this is exactly the type of experiments I'm interested in to understand why we do things the way we do them and challenge tribal knowledge or rules of thumb. I'm writing my very first (and hopefully longest) youtube comment here because I'd like to make a few suggestions that may make your future experiments/videos even more valuable. 1. Include information about the spread of your samples Instead of bar charts, I suggest using "box plots" as they are a common way to display information about the average and the spread of the samples together. With few samples like here, you may also just overlay the individual samples over your bar chart, but I'd still prefer some of the statistics that a box plot has to offer. Why this is important: you concluded that 4hr clamping is sufficient for you, because in average the joint is just strong enough, without considering how consistently this is the case. But would you still make the same conclusion if half of your samples are very weak and half of them are very strong, resulting in a just strong enough average? 2. Validate your assumptions The underlying assumption you make here is that with 24hr of clamping, the joint is as strong as it gets and it is still weaker than just wood due to being stiffer. It would be interesting to see experiments with more than 24hr clamping time to validate (or invalidate) that the strength does not increase further. Why this is important: assuming after 48hr of clamping you can double the strength compared to 24hr clamping, would you still just clamp for 24hr if you have a project where strength matters more than clamping time? 3. Separate potential causes to make fair comparisons Your experiment with hand clamping and letting the piece dry clearly shows that there are at least two major causes for joint strength. One of them being the clamping time and the other being the total drying time. I think these can and need to be separated in that you test the strength after the same amount of total drying time for all the samples. If you can keep all the variables except for one fixed, you can show which has how much impact. Why this is important: what if the clamping time has almost no impact (as long as there was some) but it's really only the total drying time that matters? I.e. would you still do 4hr clamping if after 1hr of clamping and 24hr total drying time you get the same strength as with 24hr clamping/drying time (Your hand-clamping experiment potentially indicates that this could actually be the case)? When repeating such an experiment I suggest to first find the clamping time that results in maximum strength and take that as a reference. Then, try different clamping times but keep the total drying time the same as the one that reaches maximum strength before testing the samples. And in the analysis, also show the spread of the different samples ;)
Nice Video. As a retired pro a note from experience. I would be sure my joint was good. No bow. Test by clamping one end lightly and examine the gappage at the other end. Apply glue and put boards together and wait so glue is absorbed on both boards. Then clamp. If you have use lots of pressure to bring the joint together, you are introducing stress into the panel. Fix your jointer. Glue introduces moisture into the wood. Remove as much squeezed out glue to allow the joint to dry out faster. I'd clamp for an hour or more. After removing the clamps I'd wait at least 24 hours before secondary machining. NOTE!!! You have added moisture to the wood so the wood at the joint will swell. WAIT!! as long as possible before sanding or planing the joint. Too soon and the joint will continue to shrink and you will have a slight valley at the joint.
Thanks for a very good video. I glue up segmented bowls and vases etc with a glue joint approx 20mm wide, then I turn them on the lathe down to a wall thickness of 6mm 1/4inch and I don't have failures . But I glue things in an un conventional way.. I apply the glue to the surfaces and let it sit for a minute to soak in, if there are any dry spots I apply more or just spread it with my finger. Then I clamp up tightly. I don't have to worry about starving the joint of glue because the wood had time to absorbe it before clamping. I clamp for an hour, and I'm very careful to avoid temperatures below 12°C I bring the glue into the house overnight. By the way, this joint will GRAB very quickly, so you must have the parts lined up and the cauls and clamps ready in advance. If you disturb it after it grabs the joint will fail.
My approach has long been, clamp overnight if there's no reason not to, clamp 4 hours when convenient, and clamp 2 hours when I need the space or clamps for something else. Regardless of the clamping time, I expose the joints to minimal stress for 24 hours. That doesn't mean I don't touch them though. Sometimes I'll start combining subassemblies into a larger project after 2 or 3 hours of curing time if doing so involves minimal stress on the glue joints. I've never run tests on the joint strength, but I've never had an unexpected joint failure either. 30 years of experience suggests 2 hours of clamping is adequate for normal joinery and normal use.
Thanks! I have had bosses insist on running things through the planer after 15 minutes, but I always had other thing to do in the meantime to let them sit for a while longer. About an hour into the glue up, when the glue is somewhat still soft What I have been doing is removing clamps one at a time to remove the glue and then replacing them from the panel. So instead of releasing any pressure is to keep the clamp about ½ an inch above the wood to be able to scrape the glue off. One thing I have been doing for years now is to let the panels sit for a week to allow any water from the glue to evaporate off the wood. When first glued the panels have a swelling like a mountain ridge and if you were to plane or sand it flat, it then dries leaving a valley.
When PVA glue "dries" it is polymerizing. The solvent (water) evaporates, It was keeping the glue from polymerizing. It is analogous to a crystal without such a regular, repeating pattern. When the glue is drying and the polymers are accreting into a solid it forms up in a more or less orderly manner. If the pressure changes in the middle of that process, it will interfere with the orderly manner and introduce a defect in the glue. Any polymerization already finished cannot shift - it is already essentially solid. The glue that is still solidifying will be torn away from what it was trying to connect to, which creates a very tiny rift that is not mended by liquid glue. It is too small for that and surface tension prevents it from entering these tiny fractures. These tiny fractures will reduce the strength of the glue joint wherever they exist, and if there are enough of them it will significantly undermine the strength of the joint. They probably will be lined up because the evaporation happens more from where the glue line meets the air and less from inside. So there is a wave of hardening traveling through the joint, but not too orderly, probably. So when the pressure changes because you remove the clamps, you're introducing tiny fractures wherever the glue was not cured. This is better avoided by waiting long enough for the glue to cure. I don't know why TB would recommend 30 minutes. It isn't enough time if the pressure will change. The reason the hand-pressed or taped glue-ups work so well is because the pressure doesn't change.
Your joinery was very good and the extremely smooth surfaces obviate the need for high-pressure clamping. If you use wood that is less smooth, the clamping pressure helps the glue penetrate into the pores, cracks and defects in the surface of the wood. A rougher surface can result in a stronger glue joint because there is more surface area for the glue to touch, and the cured glue is physically locked into the pores. Glue is already stronger than wood, so the payoff isn't that great. But, it takes more work to make a super-smooth surface like you made, so you can save that effort for a glue up. Jointers often produce a less than furniture-quality edge, but it is ideal for glue--ups. So, the results you got were influenced by how smooth the wood actually was. That is not a problem, that is a feature, because it removed from the equation the "smoothness" or "roughness" of the wood, which is difficult to characterize. But, clamping pressure becomes more important when the wood is less smooth. To the extent that the glue is filling any gaps, clamping pressure matters more. Another reason clamping matters is that the project can warp or shift while the glue is drying. This can ruin a project. Clamping can prevent movement (if that is a goal and it is done right, of course). Clamping can also force the parts to shift, so extra clamps and/or cauls are needed to prevent any movement.
Valuable, thanks for posting. I usually clamp for an absolute minimum of 2 hours with Titebond III, preferably four. If I am building something where the joint will be stressed, I allow the 24 hours that Titebond recommends. For my boxes, where the corners are not stressed, I can continue after the minimum 2 hours clamp time. The most shop efficient thing would be to glue and clamp at work day's end, let it go overnight, then continue in the morning. Bullet proof.
Great video, and I always appreciate anyone who tests conventional wisdom to see if it really holds up. Some years ago I was doing a project of making wood covers for baseboard heaters. It was all made out of poplar but required a ton of glue ups. But all of them are under low stress. I found that just holding the pieces together with my hands for 5 minutes was sometimes sufficient. 4 years later none of these glue joints have failed. Typically, I prefer to leave major glue ups in a clamp for 8-24 hours. But for minor things, where the wood will be under low tension and not see serious abuse, then shorter clamp times work just fine.
thanks. really well done. releasing clamps after 30mins releases pressure and weakens the glue. Personally I: put a few clamps on & leave them on overnight.
Wow, heck of a video on wood glue. You answered a huge number of questions I’ve asked myself, clamp time, fit, etc.. Great video, thank you. Looking forward to your next vid, you a great job at explaining what you’re doing, why, and the editing is very good. Thank you, a woodworker from Missouri.
I watched this after seeing the joint testing video you did with Scott Walsh, and you've definitely earned my subscription! I only own a few clamps and I'm definitely one of those who leaves them on overnight if not a full 24 hours so knowing this will help ease my anxiety about taking them off sooner. Thanks, and I look forward to seeing more of your testing videos!
I've been making panels out of pallet wood. Planed faces, some bowing, heated but not too warm shop, Titebond 3. I have have a limited amount of clamps etc, so I can only do 1-2 panels at a time. I leave them in clamps for about 90min. After that they are pretty solid, but I can still easily scrape the squeezeout off. Next day they are good and ready to go in the planer. I have done about 30 boards like this and so far no problems.
I think what happend in the last test is that when you released the clamps - the structure of glue was weakened by the released wood and when the glue hardened it was already damaged by this clamp-release movement.
Thank you for sharing this video and taking the time to test. I know how hard this is. In my opinion, testing end-grain glued joints would be far more interesting as the joint would break mostly at the glue site and not the wood itself. That would truly show the glue up's strength. It was also previously shown that despite the old belief, end grain glue-up is far stronger than along the grain.
You make a really good point in better isolating glue set time and strength by gluing end grains instead. Unfortunately the reason i did not pursue it is because end grain to end grain glue up is not as common in a typical woodworking projects and I think people would find it a bit harder to follow the logic.
Great testing. Another factor I have found (50 years since I was an apprentice) that you mention is glue line thickness. We used to do panels with no clamps - rubbed joint. It would interesting to compare - several panels clamped together and several with a rubbed joint. For those unfamiliar, take the 2 pieces with good glue joints, glue the edges and press the joints together to ensure glue spread and also squeeze out any excess glue (with experience you should be able to apply just the right amount of glue for a .003 to .006 thick glue line) then stand the “panel “ on edge allow to dry. For wide panels lean 2 sticks against the wall to support the panel at a nearly vertical angle.
I've seen a couple of your stress tests and I have one compliment on your test setup. A lot of videos that I see people doing similar tests they use a luggage scale and try to capture the readout with a camera to find the frame with the highest reading. Your setup is much better because of the peak-hold feature of your scale. LCD displays, especially on inexpensive luggage scales have a fairly slow refresh rate so the actual peak reading may never show on the LCD. The peak hold of your scale will actually capture the peak reading even if it happens between LCD refreshes. Thank you for the quality of your test setup.
One thing that most folks overlook: the roughness of the glued surface. If your surface is too smooth and clamped tightly it’s easy to force the glue out. I wonder what the impact would be when sanding/roughing some nooks and crannies, or scrape/cut shallow grooves? How rough of surface is enough? How much is too much? How does it affect cure time? There’s one lazy trick I’d love to see tested: prevent glue starvation: let glue air dry until tacky (5-15 minutes) then clamp and clean with rag and *warm* water.
Yes! You make valuable, quality video, Suman. Doesn't matter if they don't come out often. Good stuff is worth waiting for, and it can only come as you are able, not as others wish. Very helpful to quantify the time effects of clamping glue-ups. Adequate clamping pressure, released at 4 hours but NOT disturbed for 24, and on to the next tasks. It would make sense to have left them all for 24 hours as directed, to see if it matters when the clamps were removed. I suspect it wouldn't matter so long as the glue lines were intact. You are so right that the quality of the edge match is most important. And that means you don't need a clamp every 3 inches either. I glued a 3 piece panel of cheap wood with jointed edges for a painted sign that rotted away after 15 years in the rain, snow & ice. But it never came apart. Thank you so much!
Most of my glue-ups are segmented rings for wood turning. This is useful information to me, especially allowing the joints to cure for 24 hours. This will speed up my assembly process while still producing a strong, safe bond.
Love this, I think not touching the joint after clamping is the most important. Often I take the clamps off after 2 hours if I have a lot of glue ups, and not enough clamps(as no one, no one ever, has enough clamps). Great video, love science.
What I find funny about this is that it tracks with my experience and practices. I always assumed cure time was the major factor, and clamping is mostly to ensure the most surface area for the glue is being contacted before it sets up enough to hold that pressure itself (how sprung joints work). I typically take my clamps off after 3-4 hrs as I only have a few, and unless the wood is particularly "featured" I really don't want to leave them overnight in those clamps.
Thank you for putting in all the time and resource's to show us the results. You have triggered me now to try my own tests on the rub joint of old, I think this may be interesting.
To me the most interesting element of these tests is the no clamp test. I've seen some great videos discussing clamp pressure. Over time I've reduced my clamp pressure. I now clamp to achieve squeeze out and typically unclamp after 20 to 25 minutes and put the piece aside over night.
I wonder if greater clamping pressure causes more glue to squeeze out, but then if that clamping pressure is released before the glue dries/cures enough to hold the joint tightly together, then there joint has an effective glue deficit. Less pressure means more space between fibers, which means more glue is needed.
Great video. Very informative. The non-clap results were very surprising to me. I'm going to think twice when I do my next picture frame...I usually struggle with a complex set of clamps trying to distribute equal pressure on all sides
The hand-clamped joints left more glue in the joint, which pulled the wood together as it shrank while drying. The clamping process squeezed most of the glue out and glue was wiped away. As that tiny amount of glue shrank, it was replaced by air, which is weak as you can get. Thanks for this excellent testing !!! 😊
Should have mentioned the spring-back / rebound of wood after removing clamp. With no force applied this rebound would suck in air, since all the glue had been squished away. Having excess glue would pull the wood together as it shrank, and because of extra glue, no air gaps.
Great info, you saved a lot of extra glue time, and clamps. I always wondered about using tape on glued miter joints, now I see some proof thanks to you.
For the 30 min clamp, then 24 hour cure, perhaps the clamping force being removed after the glue began to setup (but not fully cured) broke some of the glue bonds as the wood 'rebounded' elastically after clamping. This would render at least part of the glued surface ineffectual at the bond interface. Based on the hand fit-up and 24 hour cure, it begs the question "are we typically clamping with too much force?" Excellent video, well done!
Edit* I probably shoulda finished the video before commenting haha. In any case, I'd be interested to see the differences anyways! Amazing video! What I'd be interested to see is this same test, except instead of trying to break the joint immediately after the clamps are removed, let the glue fully cure To avoid confusion here's an example. Clamp the wood for 5 minutes, remove clamps, and let glue cure for 24 hours. Come back and test the joint.
@WoodcraftBySuman I edit my comment if you didn't see. I should be more patient and watch the full video before commenting haha. In any case, I completely understand. I have some limited content creating history and I know first hand the limiting factors of being small and just not having enough time to do everything you'd like to do! Still, amazing video. Youve just gained another sub for what it's worth 😊
Good information.. been gluing various stuff for almost 30 years now… I always questioned the TH-cam gurus who took clamps off quick.. I always leave overnight and never had issue.. plus your point of well fitting joints is key.. my uneducated guess is pressure release from taking out of clamps or hands let’s glue gap increase.. there is info on gap strength and limits … again beyond what I can process.., but I never had a glue joint fail drying overnight.. looking forward to next test vid.. thank you .. enjoy the tiny human.. they’re the best .. u can’t clamp or glue then tho ..
I love the scientific approach you've brought to your channel. There are so many possibilities for things to test in the shop, I always look forward to what you'll test next!
I love Titebond III. However, I have believed - from my woodworking experience [I used to be a luthier] and am now a woodcraftsman - that it is weak unless it is left undisturbed for 24hrs. After then, it is an excellent bonding agent, and as you have shown, only 4hrs is necessary for reliable strength. But good to have your scientific experiments to draw from, really appreciate it. Great work, thanks.
Bravo, sir! This is an excellent approach to the scientific method--you control for the things you can, account for extremes in deviation, and publish your results in an easy to understand way while acknowledging constraints. I'll definitely be reducing the clamping time between phases now that I understand this. I mostly make picture frames and smaller jointed items anyway. If something is clamped for 24+ hours, it's not a big deal, but I won't worry about the joints being too weak after 2-4 hours, so long as no additional stress is added in that time.
My assumption about the hand clamp vs the 30m clamp is that mechanical clamping forced most of the glue out and before it had enough time to set the wood sprung apart enough to leave microscopic gaps. I have no way to prove this though.
I agree. Feels like the most plausible reasoning. at the end of the day, any of us could disturb the 30min clamp project enough to weaken it. Best to clamp it longer till the glue strength really kicks in.
Saved me a pile of testing , thank you. I am also sharing because I think someone who takes the time to do testing is a valuable asset to any wood workers out there.
Titebond 3 cures more slowly than the other versions and Titebond 2 is the fastest cure. I glued thousands of glue line feet in red oak in the 90’s using TB2 because it allowed me to reuse my clamp rack sooner. I left it in the clamps for 30 minutes, then stacked the panels to cure 24 hours before thicknessing. Several factors contributed to the success of my efforts. First was the joints were right off the tablesaw, not planed. The surfaces were decent but not perfect. I believe that this helped prevent a starved joint. The hand-planed joints in the video did not require high clamping pressure, and too much pressure can starve the joint. Second factor is environmental. These were glued in Colorado where the air (and the hardwood) is dry, so moisture from the glue rapidly moves into the wood and the shop air, faster than in a more humid location. My gluelines never failed and I regularly broke cutoffs to verify that the joints were stronger than the oak I’m doing glue ups now in a 75% relative humidity shop with acclimated wood and Titebond 3. I leave the clamps on 12 hours minimum and wait another 12 before planing to prevent sink at the glue lines.
I think you're missing the 30 clamping point. After 30 minutes, most joints are ready for the clamps to be removed. That can be good since the clamping pressure can distort the wood and removing before complete glue setup allows the wood pieces to relax and flatten out.
Nice work! I have heard it said that a rub joint is plenty strong. It's not quite your clamp-free treatment, but that lore (and my experience) are consistent with your results.
Wow, what a good video. As someone who has worked in destructive testing for years, your methods are pretty much as spot on as possible given the variables in material. Now, next task (for me, at least) would be to determine the optimal amount of glue per square cm (sorry, am in Europe so we use metric) for the Cherry used. Then compare that to less and more porous timbers. I see a whole series of videos here!!
Agree, when releasing the clamps wood have a tendency to "swell" if I can put it that way. and well half dried glue the stretches and creates air pockets or pulls away from the micro bonds its made with the wood.
I have watched a couple of your videos now, and I like the common sense scientific approach you have for wood working and for testing wood working. Bonding materials together is an incredibly complicated science, but you got the broad strokes correct. Key take-aways 1) Bonds continue curing for a long time; 2) Just because the failure isn't in the bond, doesn't mean the bonded joint is as strong, 3) the feel of the joint doesn't indicate strength. Also, I'd say that what you are really showing is when it is "good enough". There are obviously too many variables to test for without a research grant, but I think this was a key thing to test and will serve as a good caution for impatient wood workers. BTW the process you used for testing (isolating a single variable, testing a range of values, and definitively stating this may not hold for other materials) is great, especially in the age of TH-cam. In a real test, you would have needed significantly more samples (for material characterization they may do 100 tests or more). Also, while your test setup was very practical and very similar to a case that matters to wood workers, it is not very good for testing the bond. Being off from the bond one way or another will dramatically change the loading through the bond. You are also testing a complex loading, it isn't shear (sliding the two pieces along the bond) or tension (pulling them directly apart) or pure bending (which is really tension on one face and compression on the other). If you are interested, a 4 point bend test would be a "better" setup since you have consistent load between the inner two points, instead of a strong peak at the center. All that being said, I have seen science journal articles that are less well done than this.
I found this video really interesting. As a side note, this "joint is stronger than the material" problem creates what we call in welding "stress risers," and we get the same results - cracking in the immediate vicinity of the weld but not the weld itself.
The real question is not how strong the joint is after clamping for 5 minutes, 30 minutes, etc. but how strong is the joint 24 hours after clamping for 5 minutes
Good video.I too have done hand pressure clamps.Masking tape clamping and spring clamp and had good results.I definitely agree that a lot of creators go way overboard with clamping.I have made lots of edge grain cutting boards and used maybe 6 clamps and never had a fail
![[MV] A leap of faith...ความเชื่อใจครั้งสุดท้าย (From "Petrichor the series")](http://i.ytimg.com/vi/U1piZH2CNXA/mqdefault.jpg)
Great video!! Here's my theory. When the clamps were removed after 30 minutes, the glue hadn't cured enough to compensate for the release of pressure. The boards pulled apart just a little bit on their own and messed up the glue. When you just pushed the boards together and left them, there was no change after 30 minutes, so the joint was stronger. Maybe?
Was thinking the same thing
Hadn’t read your reply before my post, totally agree.
Agreed, to look at it another way, the clamps squeeze out far more glue than the "hand pressed" version, so when the pressure relaxes to "clampless", there is less glue in the joint than the hand pressed version, but a wider gap than the long-term clamped version.
Yep. My thought as well. Don't know for certain, but glad to be part of the majority consensus hah
Not even a question. The glue has not fully cured in less than 24 hours. It achieves a minimum working strength in 30 minutes.
I was a research engineer for 10 years designing and carrying out experiments, and a woodworker since before that. This is one of the most complete and robust scientific woodworking experiment videos I've seen. Controlling for all sorts of variables via sensors that most others would ignore. Thank you for this video, I and countless others will benefit from your rigor! I'm about to glue up a large table in half a dozen glue ups and this will save me days!!
Thanks dude! I could have added more variables like letting each of the conditions dry 24hrs but it takes so much material and time to do this experiment as-is. I’m glad you appreciate the consideration that went into the setup.
@@WoodcraftBySuman There are always more variables! You seem proficient at identifying and appropriately accounting for the important ones to reach practical, useful conslusions which is what makes good science. Most videos like yours are woodworkers taking a stab at being scientists, with varying success. You strike me as a scientist first, applying yourself to woodworking. Do you have a background in research?
@@FlyingMoose_ haha. Pretty solid deductions there. Yes I am a scientist - though in biologics.
@@WoodcraftBySuman Not a lot of fields that have a future in research beyond academia, biologics seems like it would be a good one. I worked in metal product manufacturing research and applications. Very large lab with lots of fabrication, inspection and data collection equipment - lots of work with load cells, they are so incredibly valuable for experiments but unfortunately very expensive! Stuff I've always dreamed of applying to woodworking so your videos resonate strongly with me, I'll be binging them over the next few days.
@@FlyingMoose_ that’s super cool! And hope you like the videos. I only have a few on testing stuff as this has been a recent pivot for the channel. I will continue to make testing or testing adjacent videos going forward.
I worked in a furniture mill in the early 1980's. When making raised panel doors with standard stick and cope construction, our rule was to leave the doors in the clamps for at least 2 hours. After that time, they could be removed from the clamps and stacked if we needed the clamps for another batch of doors. (We typically made doors in batches of 50 to 100 doors.) We were using a typical PVA glue, something similar to Titebond Original, which we bought in 55 gallon drums. We let the doors cure for approximately 24 hours before doing any additional work on the doors (trimming to final width and length, putting an edge profile on them, sanding, etc.).
I follow the same practice in my shop today. I leave a glue-up in the clamps for at least 2 hours and don't stress the joints for about 24 hours. I've never had a glue joint fail when following these procedures. (Except for the time at the Furniture Mill when someone stored a 55 gallon drum of glue outside, overnight, in sub-zero temps. None of the joints made with that glue held! PVA glue is ruined by freezing.)
Ruined by freezing, eh? Guess I should be throwing away all the bottles that sat in the garage over the winter and experienced repeated freeze thaw cycles. Not a lot of glue, but a couple of small bottles from when I couldn't find the last one and just bought new.
Could be that the glue was still cold when applied
No. We confirmed with our supplier that freezing ruins PVA glue. If your glue freezes, simply throw it away. There’s nothing that can be done to make it work after that.
Dang iI ust glued up a bunch of things with my titebond that was stored in my non heated garage. Great now I have to find a new spot to store my glue.
I can attest that frozen wood glue does not work that well after thawing.
I’ve also accidentally let CA glue freeze and that stuff is worthless after that
Great info. I think one important point was unstated or understated: the piece without clamps was not disturbed. We saw how little force was required to break the joints when the glue had not dried yet. Clamps hold the pieces together so that they don't come apart from something as minor as bumping the table that the glued pieces are on.
Edit after watching again: the proper testing would have been to clamp for 1, 4, and 12 hours - then waiting to test until the glue had cured at 24 hours. While 30 minutes was shown to be too little, it was not shown what happens at 1, 4, or 12 hours. The assumption that 4 hours is enough is merely assumed.
I agree with you that a second subset of 1hr, 4hr, and 12 hr clamp time with full 24hr cure would have added better data for consideration on this video.
Two reasons why I did not do that: 1) it makes the video longer and slightly more complicated to follow. I have to consider average view duration and retention times when making videos on youtube. 2) it would take a lot more wood and I felt bad wasting so much wood as-is. Because 4hrs is able to get strength that competes with the strength of the fibers itself, it is a reasonable conclusion to make that 4hr clamp time generates strong enough joint to remove clamps at room temps and 200psi.
Tests like this are just that: tests. How I chose to break the joints is not necessarily analogous real world conditions. Some people glue up in 65F shops and others in 85F shops -- this will have a huge impact on clamp time needs. There are certainly other ways to test this topic and I may even explore it in future videos. Thanks for watching.
@@WoodcraftBySuman Thank you for your tests. They are not only entertaining, but do give us more data.
Jupp, this is how it should haven been tested. No need to leave a glue up for 12-24hours in the clamps. Clamp for 2-4 hours and let the glue dry for 24 hours before applying thr full expected load. Assembly can continue after the 2-4 hours, if you don't stress the glue line to much.
When you get to the point where the wood fails instead of the glue, that's all the testing you need.
@@WoodcraftBySuman I can see that work and time and material has to be finite and you have to stop at some point. However your argument about "viewer retention" is unfortunate. Good methodology is like good workmanship quality: A bit of a pain to follow through with, but viewer retention through reputation is worth much more IMO. Compare for example to "Project Farm" testing. Always super meticulous. And look where it got him! (Just speak faster and edit more? 😁)
As a mechanical engineer I applaud your approach and execution. As a long time wood worker I just found the answer to a question I have wondered about for 50 years. Congratulation, Suman, you deserve a big thanks.
My rule of thumb from a practical and time efficient standpoint was to clamp up in the evening and let dry overnight then release and carry on the next morning. Has worked for me for decades.
That's the overall best way to do it.
I try and plan my glue ups the same way.
Testing that actually uses multiple samples and throws out the top and bottom? Here on TH-cam? Amazing!
Seriously, I find it so refreshing to see a real effort to apply the scientific method. Thank you!
(I've wanted countless woodworking videos here, but this is the first of yours. I subscribed.)
Do you have a reference for where the "throw out max and min, average the rest" approach comes from?
That is a pretty common approach to doing simple statistics. The idea behind throwing out the extremes is to remove the cases where something unusual happened, letting you focus in on the most common examples. When I googled it I mostly got examples of how to do it using tools used for such analysis (Excel spreadsheets, MATLAB) rather than WHY. Which supports the idea that it is common, since so many questions about how to automate it have been asked.
@@somebodypeculiar Thanks for looking into it! That's also what I found. I was hoping there was some statistical rule of thumb that outlined the why. To me, it seems like just lopping off the top and bottom gives an artificially high confidence in your data's consistency. I'm not good at statistics though, so that's why I ask.
Actually, removing the extremes is often a sign of a lack of confidence in the quality of the data. Measurements that are way off from the rest can be the result of a bad measurement. Or they can represent failure of an experimenter to repeat the process consistently. It is a rough-and-ready approach to trying to reach a good rule-of-thumb, rather than a rigorous statistical process. For that matter, the average (mean) isn't always the best measure to use; the median is often preferred, where half the samples are above that point and half below. Note that while the drop-on-from-each-end approach can change the average, it can not change the median.
@@somebodypeculiar So it's like a quick and dirty way to try to limit the influence of outliers without having to actually know how to identify true outliers. I think I understand why people use it better now, thank you.
Love your scientific approach to woodworking. We need more channels like yours. Great info with practical uses. Thanks for your content.
I'm glad that I can safely free up my clamps in shorter intervals, since I started woodworking I'd usually leave glue-ups for 8 hours. Great video! The pacing of information throughout was perfect.
For the 30 min clamp 24h dry --> The wood changed shape after unclamping, but the bond was not compete. The wood applied a separating force that the glue could not expand to fill. This is partially driven by the moisture from the glue entering the wood.
Id like to see a follow up on this video on what is the minimal amount of glue needed to secure a joint vs drowning a joint.
I second this nomination. I've always wondered that myself. But like Suman says, Im putting possibly too much glue, and relying my choking of my clamp handles to squeeze out what it doesnt need. I'm a drowner, but have found the only downside of this is cleanup time, and using more glue. But I'm a weirdo, and enjoy the glue scraping/cleaning process....its cathartic.
As a non-woodworker who frequently puts bits of wood together, I'd also like to hear/see the results of flood v's sparing. As well as that, what about the effect of lightly moistening the joint face with water (to open the pores) before applying the glue?
This is a super helpful video ! I didn't realize how much risk I was taking unclamping my glue ups at 30 minutes. You've probably saved many people at least one project disaster. Very through analysis !
I am so glad you did the hand test, because I cannot tell you how many times people have told me 'you should clamp that'. I usually just use tape on veneer repairs (small pieces) unless it may shift. Its always been fine. Thanks for the video!
Honestly that was also my biggest takeaway from the video.
I feel so much better about my projects held together by painters tape.
Great vid, I’m sure this will be very useful and informative to a lot of people including myself!
My totally unscientific thought on the 30 min/24 hour surprise breakage is that maybe it could be that when the pressure is released before the glue is fully cured, the wood slightly ‘rebounds’ when the clamp is removed and causes a sudden shift in force that might upset the bond, whereas an even pressure scheme for the entire cure time wouldn’t experience such disturbance in the forces and glue line.
Just a thought for future vids - it would be nice to have a text layover of the test conditions (clamp time etc) during the part of the video where the breakages occur in the testing. Good for easily distracted people like myself to see where we’re at.
Keep up the great work, I love this channel!
I agree, in fact releasing multiple clamps one by one causes serious unbalanced pressure on the joint line.
I came here to say the same thing. This absolutely what happened.
+1
+2
Excellent video! Two thoughts of mine you didn't ask for 😬 :
- It would be helpful to see how all those clamping times fared with the recommended 24-hour unstressed period after removal from clamps (or perhaps a period that would add up with clamping time to 24 hours total to keep all the samples identical in total cure time). If the full day of curing took the 30 minute clamped batch halfway to the strength of the 24 hour clamped group, I'd be fascinated to see how, say, the 1 hour or 4 hour group would fare after the full 24 hours. Either case would still free up clamps much sooner then the common "clamp for a day" thing a lot of us do.
-The hand-clamped results are fascinating! I'd love a comparison between those where you just pushed them together to a sample group you joined with rub joints. Would the atmosphere offer greater pressure in that regard? Would the joint be any noticably different from your first group?
Again, amazing work, man! You more than earned this sub.
Love how thorough you were with this. You have saved me from the worry of "Have I clamped this long enough" I was at overkill with overnight glue-ups lol. Thanks Suman.
Wow! No fluff, only the good stuff. Literally packed a 30 minute video into 10 minutes. Played at 1.5x that's less than 7 minutes! You won't find a video packed with more info per minute. Took me longer to write this comment than watch the vid - very well deserved. How could I not subscribe? Genius! Thank you man - been prayin for vids like this!
I'm a cabinetmaker.
When I was an apprentice, and going to trade school, I was taught that a properly glued joint (not too much glue, not too little) needs to be in the clamps for at least 10 minutes. And properly clamped of course. So not too much force, where you're squeezing all the glue out, and not too little force, where it's not even doing anything.
In practice, I like to keep clamps on at least one hour. If it's something big and complicated, I leave it overnight.
It's also important to note that regular white PVA glue is perfectly strong enough to use for furniture, as long as the joints are put together as I've described.
Yellow glue, or "carpenter's" glue, also known as aliphatic resin, is typically a stronger adhesive, as it's meant for structural purposes.
Titebond III is an exterior PVA, but I've noticed it is thinner and runnier than regular PVA, and it definitely needs more than 10 minutes in clamps.
I have a video suggestion for your test rig. It would be cool to see testing done to compare fluted dowels, spiral dowels, regular dowels, and maybe miller dowels too for the fun of it. I'm curious if the friction of a regular dowel causes glue starvation, or if the different types of dowels cause any significant difference in strength in the joint. I've never seen anyone test this before and many woodworkers use dowels in their joinery.
Love the process you used, I'm 60+ years old and spent my life thus far as an engineer asking the questions you asked. Well done! About to retire and spending more time in the wood shop, been thinking about my glue ups, hum... and you just did 700% of the work. Thank you so much. Youre awesome, thank you. Honestly, I think you out engineered Tightbond on their instructions, and you were very graceful, well done.
As an owner of a WW business, (and an even smaller YT channel than yours...lol) this is very helpful information. I got into the habit of writing the time on my glue-ups and waiting about 3 to 4 hours with only enough clamping pressure to get squeeze-out along the entire edge. As to the LAST TEST...my theory would be that the initial pressure squeezed out most of the glue and then releasing that intense pressure left the joint a little "glue-starved" for final curing.
Hand-clamping kept enough glue in joint so it was not replaced by air (spring-back / rebound of wood sucks in air). You're right about "glue-starved".
This males perfect sense. there may even have been air ingress once the pressure was removed from the glue starved joint. I'd love to see a magnified shot of the break
As an engineer myself I have to say: Perfect execution! 🤩I love how you put attention to all the details! And the results are also very helpfull ... thanx for investing your time. 👍
A lot of woodworkers suggest clamping for 1 hour, but then not stressing it for 24 hours. Curious how those results might fair
But from this - I guess it'd be not much different from the hand clamp test! Interesting
You mean the directions on the bottle that he quoted and then summarily ignored?
This is an excellent video on glue ups. I usually wait at least 1 hour before handling or working with glued material on fast moving projects, but now will wait longer after seeing you video. Thanks a million
Great video quality
my hypothesis on the 30m clamp 24hr dry boards is that the clamps force much of the glue out, but the bond after 30m isn't enough to the adherants to maintain the joint and so it weakens. i've had this type of result when overclamping joints, wiping up the squeeze out and then backing off some of the pressure. i had a tabletop split right down the glueline this way and ended up doing some testing to figure out why it might have happened. i found it was pretty well understood that too much pressure can starve a joint and i suspect that backing off the pressure after clamping is creating a similar situation.
Love the evidence-based approach to woodworking, Suman. Could you put error bars on your averages in future? It's important to see how much variation is caused by the test variable relative to uncontrolled variables.
Yup- I’ll need to include error bars in the future bc folks are really interested in the spread.
and do you suppose that information would at all impact your decision when it comes to gluing? I doubt it.
By clamping you push excess glue from joint. When you remove clamps after 30 minutes you release pressure on wood so a little tiny gap can occur on joint, but there is no glue to fill that gap.
So it doesn't matter that you leave it for 24 hours, joint is already weak.
When you making joints using just hands or weak pressure, you don't push so much glue out from joint, you don't store tension in wood, so wood don't try to break that joint and glue can do the job. There is probably a little more glue in such joint but it doesn't matter.
Really love your channel. I personally believe that curing time matters more than clamping time. Another video perhaps? 🙃👍
Congratulations on your very carefully controlled methodology, I hate testing videos that don't even care to make sure the samples and force applied are as equal as possible, it made me really happy to see all the care you put into this, it doesn't go unnoticed.
I like this video very much because as an engineer, this is exactly the type of experiments I'm interested in to understand why we do things the way we do them and challenge tribal knowledge or rules of thumb. I'm writing my very first (and hopefully longest) youtube comment here because I'd like to make a few suggestions that may make your future experiments/videos even more valuable.
1. Include information about the spread of your samples
Instead of bar charts, I suggest using "box plots" as they are a common way to display information about the average and the spread of the samples together. With few samples like here, you may also just overlay the individual samples over your bar chart, but I'd still prefer some of the statistics that a box plot has to offer.
Why this is important: you concluded that 4hr clamping is sufficient for you, because in average the joint is just strong enough, without considering how consistently this is the case. But would you still make the same conclusion if half of your samples are very weak and half of them are very strong, resulting in a just strong enough average?
2. Validate your assumptions
The underlying assumption you make here is that with 24hr of clamping, the joint is as strong as it gets and it is still weaker than just wood due to being stiffer. It would be interesting to see experiments with more than 24hr clamping time to validate (or invalidate) that the strength does not increase further.
Why this is important: assuming after 48hr of clamping you can double the strength compared to 24hr clamping, would you still just clamp for 24hr if you have a project where strength matters more than clamping time?
3. Separate potential causes to make fair comparisons
Your experiment with hand clamping and letting the piece dry clearly shows that there are at least two major causes for joint strength. One of them being the clamping time and the other being the total drying time. I think these can and need to be separated in that you test the strength after the same amount of total drying time for all the samples. If you can keep all the variables except for one fixed, you can show which has how much impact.
Why this is important: what if the clamping time has almost no impact (as long as there was some) but it's really only the total drying time that matters? I.e. would you still do 4hr clamping if after 1hr of clamping and 24hr total drying time you get the same strength as with 24hr clamping/drying time (Your hand-clamping experiment potentially indicates that this could actually be the case)?
When repeating such an experiment I suggest to first find the clamping time that results in maximum strength and take that as a reference. Then, try different clamping times but keep the total drying time the same as the one that reaches maximum strength before testing the samples. And in the analysis, also show the spread of the different samples ;)
Your videos mix engineering and woodworking in a way I haven't seen done on youtube before, really enjoyed this. Keep it up!!!
OH MAN. This is the deep dive I've been waiting for. Thank you for this!
Short, concise, expert advice.
Thank you. This will be my procedure going forward.
Nice Video. As a retired pro a note from experience. I would be sure my joint was good. No bow. Test by clamping one end lightly and examine the gappage at the other end. Apply glue and put boards together and wait so glue is absorbed on both boards. Then clamp. If you have use lots of pressure to bring the joint together, you are introducing stress into the panel. Fix your jointer. Glue introduces moisture into the wood. Remove as much squeezed out glue to allow the joint to dry out faster. I'd clamp for an hour or more. After removing the clamps I'd wait at least 24 hours before secondary machining. NOTE!!! You have added moisture to the wood so the wood at the joint will swell. WAIT!! as long as possible before sanding or planing the joint. Too soon and the joint will continue to shrink and you will have a slight valley at the joint.
Great video!!!! I am in the middle of a glue up and got curious. It’s awesome to see someone cover a topic in such detail. Thanks for the info!
One of the best wood working videos I’ve ever seen. Great job. Very helpful.
Dude thanks so much! Thank you for watching
Thanks for a very good video. I glue up segmented bowls and vases etc with a glue joint approx 20mm wide, then I turn them on the lathe down to a wall thickness of 6mm 1/4inch and I don't have failures . But I glue things in an un conventional way.. I apply the glue to the surfaces and let it sit for a minute to soak in, if there are any dry spots I apply more or just spread it with my finger. Then I clamp up tightly. I don't have to worry about starving the joint of glue because the wood had time to absorbe it before clamping. I clamp for an hour, and I'm very careful to avoid temperatures below 12°C I bring the glue into the house overnight. By the way, this joint will GRAB very quickly, so you must have the parts lined up and the cauls and clamps ready in advance. If you disturb it after it grabs the joint will fail.
My approach has long been, clamp overnight if there's no reason not to, clamp 4 hours when convenient, and clamp 2 hours when I need the space or clamps for something else. Regardless of the clamping time, I expose the joints to minimal stress for 24 hours. That doesn't mean I don't touch them though. Sometimes I'll start combining subassemblies into a larger project after 2 or 3 hours of curing time if doing so involves minimal stress on the glue joints. I've never run tests on the joint strength, but I've never had an unexpected joint failure either. 30 years of experience suggests 2 hours of clamping is adequate for normal joinery and normal use.
Thanks! I have had bosses insist on running things through the planer after 15 minutes, but I always had other thing to do in the meantime to let them sit for a while longer.
About an hour into the glue up, when the glue is somewhat still soft What I have been doing is removing clamps one at a time to remove the glue and then replacing them from the panel. So instead of releasing any pressure is to keep the clamp about ½ an inch above the wood to be able to scrape the glue off. One thing I have been doing for years now is to let the panels sit for a week to allow any water from the glue to evaporate off the wood. When first glued the panels have a swelling like a mountain ridge and if you were to plane or sand it flat, it then dries leaving a valley.
When PVA glue "dries" it is polymerizing. The solvent (water) evaporates, It was keeping the glue from polymerizing. It is analogous to a crystal without such a regular, repeating pattern. When the glue is drying and the polymers are accreting into a solid it forms up in a more or less orderly manner. If the pressure changes in the middle of that process, it will interfere with the orderly manner and introduce a defect in the glue. Any polymerization already finished cannot shift - it is already essentially solid. The glue that is still solidifying will be torn away from what it was trying to connect to, which creates a very tiny rift that is not mended by liquid glue. It is too small for that and surface tension prevents it from entering these tiny fractures. These tiny fractures will reduce the strength of the glue joint wherever they exist, and if there are enough of them it will significantly undermine the strength of the joint. They probably will be lined up because the evaporation happens more from where the glue line meets the air and less from inside. So there is a wave of hardening traveling through the joint, but not too orderly, probably. So when the pressure changes because you remove the clamps, you're introducing tiny fractures wherever the glue was not cured. This is better avoided by waiting long enough for the glue to cure. I don't know why TB would recommend 30 minutes. It isn't enough time if the pressure will change. The reason the hand-pressed or taped glue-ups work so well is because the pressure doesn't change.
Your joinery was very good and the extremely smooth surfaces obviate the need for high-pressure clamping. If you use wood that is less smooth, the clamping pressure helps the glue penetrate into the pores, cracks and defects in the surface of the wood. A rougher surface can result in a stronger glue joint because there is more surface area for the glue to touch, and the cured glue is physically locked into the pores. Glue is already stronger than wood, so the payoff isn't that great. But, it takes more work to make a super-smooth surface like you made, so you can save that effort for a glue up. Jointers often produce a less than furniture-quality edge, but it is ideal for glue--ups. So, the results you got were influenced by how smooth the wood actually was. That is not a problem, that is a feature, because it removed from the equation the "smoothness" or "roughness" of the wood, which is difficult to characterize. But, clamping pressure becomes more important when the wood is less smooth. To the extent that the glue is filling any gaps, clamping pressure matters more. Another reason clamping matters is that the project can warp or shift while the glue is drying. This can ruin a project. Clamping can prevent movement (if that is a goal and it is done right, of course). Clamping can also force the parts to shift, so extra clamps and/or cauls are needed to prevent any movement.
Valuable, thanks for posting. I usually clamp for an absolute minimum of 2 hours with Titebond III, preferably four. If I am building something where the joint will be stressed, I allow the 24 hours that Titebond recommends. For my boxes, where the corners are not stressed, I can continue after the minimum 2 hours clamp time. The most shop efficient thing would be to glue and clamp at work day's end, let it go overnight, then continue in the morning. Bullet proof.
Great video, and I always appreciate anyone who tests conventional wisdom to see if it really holds up. Some years ago I was doing a project of making wood covers for baseboard heaters. It was all made out of poplar but required a ton of glue ups. But all of them are under low stress. I found that just holding the pieces together with my hands for 5 minutes was sometimes sufficient. 4 years later none of these glue joints have failed. Typically, I prefer to leave major glue ups in a clamp for 8-24 hours. But for minor things, where the wood will be under low tension and not see serious abuse, then shorter clamp times work just fine.
thanks. really well done. releasing clamps after 30mins releases pressure and weakens the glue. Personally I: put a few clamps on & leave them on overnight.
Hi Suman
Very cool that Scott collaborated with you.
You are our scientist!
Thank you
Ed😊
Haha thanks. We are friends in real life.
Very very informative! You answered nagging questions that I’ve had for decades! No more overnight clamping for me!
Wow, heck of a video on wood glue. You answered a huge number of questions I’ve asked myself, clamp time, fit, etc.. Great video, thank you. Looking forward to your next vid, you a great job at explaining what you’re doing, why, and the editing is very good. Thank you, a woodworker from Missouri.
10 minutes were very enjoyable and time flew by. Thank you, it was a useful video. Be safe dear friend
Love your scientific approach to woodworking issues. Very professional and informative. Keep up the good work.
I watched this after seeing the joint testing video you did with Scott Walsh, and you've definitely earned my subscription! I only own a few clamps and I'm definitely one of those who leaves them on overnight if not a full 24 hours so knowing this will help ease my anxiety about taking them off sooner. Thanks, and I look forward to seeing more of your testing videos!
I've been making panels out of pallet wood. Planed faces, some bowing, heated but not too warm shop, Titebond 3. I have have a limited amount of clamps etc, so I can only do 1-2 panels at a time.
I leave them in clamps for about 90min. After that they are pretty solid, but I can still easily scrape the squeezeout off. Next day they are good and ready to go in the planer. I have done about 30 boards like this and so far no problems.
I think what happend in the last test is that when you released the clamps - the structure of glue was weakened by the released wood and when the glue hardened it was already damaged by this clamp-release movement.
Thank you for sharing this video and taking the time to test. I know how hard this is.
In my opinion, testing end-grain glued joints would be far more interesting as the joint would break mostly at the glue site and not the wood itself. That would truly show the glue up's strength. It was also previously shown that despite the old belief, end grain glue-up is far stronger than along the grain.
You make a really good point in better isolating glue set time and strength by gluing end grains instead. Unfortunately the reason i did not pursue it is because end grain to end grain glue up is not as common in a typical woodworking projects and I think people would find it a bit harder to follow the logic.
Amazingly detailed video. This is going to save me so much time (and clamps) for future projects. Thank you Suman!
Thanks Blake! I can’t wait to see the bull weave sculpture!
Great testing. Another factor I have found (50 years since I was an apprentice) that you mention is glue line thickness. We used to do panels with no clamps - rubbed joint. It would interesting to compare - several panels clamped together and several with a rubbed joint. For those unfamiliar, take the 2 pieces with good glue joints, glue the edges and press the joints together to ensure glue spread and also squeeze out any excess glue (with experience you should be able to apply just the right amount of glue for a .003 to .006 thick glue line) then stand the “panel “ on edge allow to dry. For wide panels lean 2 sticks against the wall to support the panel at a nearly vertical angle.
Excellent video! Well presented and thoroughly thought through.
Very helpfull in my current job, As a lean manager in a Staircase maker.
U also saved me Weeks of testing 🙂...
I'm already full of new ideas !
I've seen a couple of your stress tests and I have one compliment on your test setup. A lot of videos that I see people doing similar tests they use a luggage scale and try to capture the readout with a camera to find the frame with the highest reading. Your setup is much better because of the peak-hold feature of your scale. LCD displays, especially on inexpensive luggage scales have a fairly slow refresh rate so the actual peak reading may never show on the LCD. The peak hold of your scale will actually capture the peak reading even if it happens between LCD refreshes. Thank you for the quality of your test setup.
One thing that most folks overlook: the roughness of the glued surface. If your surface is too smooth and clamped tightly it’s easy to force the glue out. I wonder what the impact would be when sanding/roughing some nooks and crannies, or scrape/cut shallow grooves? How rough of surface is enough? How much is too much? How does it affect cure time?
There’s one lazy trick I’d love to see tested: prevent glue starvation: let glue air dry until tacky (5-15 minutes) then clamp and clean with rag and *warm* water.
Thank you so much for this test. As a new hobby woodworker this is the kind of video I love.
I love your perfect explanation of a well executed scientific process.
From observating your experiment, I am smarter now than I was before.
Yes! You make valuable, quality video, Suman. Doesn't matter if they don't come out often. Good stuff is worth waiting for, and it can only come as you are able, not as others wish.
Very helpful to quantify the time effects of clamping glue-ups. Adequate clamping pressure, released at 4 hours but NOT disturbed for 24, and on to the next tasks. It would make sense to have left them all for 24 hours as directed, to see if it matters when the clamps were removed. I suspect it wouldn't matter so long as the glue lines were intact.
You are so right that the quality of the edge match is most important. And that means you don't need a clamp every 3 inches either. I glued a 3 piece panel of cheap wood with jointed edges for a painted sign that rotted away after 15 years in the rain, snow & ice. But it never came apart.
Thank you so much!
Fantastic. Limited variables to 1 at a time. Love the thought out testing methonds. Just fantastic
Most of my glue-ups are segmented rings for wood turning. This is useful information to me, especially allowing the joints to cure for 24 hours. This will speed up my assembly process while still producing a strong, safe bond.
Love this, I think not touching the joint after clamping is the most important. Often I take the clamps off after 2 hours if I have a lot of glue ups, and not enough clamps(as no one, no one ever, has enough clamps). Great video, love science.
What I find funny about this is that it tracks with my experience and practices. I always assumed cure time was the major factor, and clamping is mostly to ensure the most surface area for the glue is being contacted before it sets up enough to hold that pressure itself (how sprung joints work). I typically take my clamps off after 3-4 hrs as I only have a few, and unless the wood is particularly "featured" I really don't want to leave them overnight in those clamps.
This was enlightening. Congratulations on your method, the editing, the data collection and everything. Awesome work
Thank you for putting in all the time and resource's to show us the results. You have triggered me now to try my own tests on the rub joint of old, I think this may be interesting.
To me the most interesting element of these tests is the no clamp test. I've seen some great videos discussing clamp pressure.
Over time I've reduced my clamp pressure. I now clamp to achieve squeeze out and typically unclamp after 20 to 25 minutes and put the piece aside over night.
I wonder if greater clamping pressure causes more glue to squeeze out, but then if that clamping pressure is released before the glue dries/cures enough to hold the joint tightly together, then there joint has an effective glue deficit. Less pressure means more space between fibers, which means more glue is needed.
I agree, soon as I saw he had transducers on the clamps to measure clamping pressure I was eager to see variant in clamping pressures tested.
Great video. Very informative. The non-clap results were very surprising to me. I'm going to think twice when I do my next picture frame...I usually struggle with a complex set of clamps trying to distribute equal pressure on all sides
The hand-clamped joints left more glue in the joint, which pulled the wood together as it shrank while drying. The clamping process squeezed most of the glue out and glue was wiped away. As that tiny amount of glue shrank, it was replaced by air, which is weak as you can get. Thanks for this excellent testing !!! 😊
Should have mentioned the spring-back / rebound of wood after removing clamp. With no force applied this rebound would suck in air, since all the glue had been squished away. Having excess glue would pull the wood together as it shrank, and because of extra glue, no air gaps.
Great info, you saved a lot of extra glue time, and clamps. I always wondered about using tape on glued miter joints, now I see some proof thanks to you.
For the 30 min clamp, then 24 hour cure, perhaps the clamping force being removed after the glue began to setup (but not fully cured) broke some of the glue bonds as the wood 'rebounded' elastically after clamping. This would render at least part of the glued surface ineffectual at the bond interface. Based on the hand fit-up and 24 hour cure, it begs the question "are we typically clamping with too much force?"
Excellent video, well done!
This was an interesting video! I liked how you did 5 samples per test.
such a great video Suman... i definitely learned a bit. your approach and execution of these tests is nothing short of amazing.
This is how a science of woodworking video is done. Thank you for being a hero.
Edit* I probably shoulda finished the video before commenting haha. In any case, I'd be interested to see the differences anyways!
Amazing video! What I'd be interested to see is this same test, except instead of trying to break the joint immediately after the clamps are removed, let the glue fully cure
To avoid confusion here's an example. Clamp the wood for 5 minutes, remove clamps, and let glue cure for 24 hours. Come back and test the joint.
Agreed. It would add more value for sure. Just didn’t have the time or capacity to double up production schedule for this video.
@WoodcraftBySuman I edit my comment if you didn't see. I should be more patient and watch the full video before commenting haha.
In any case, I completely understand. I have some limited content creating history and I know first hand the limiting factors of being small and just not having enough time to do everything you'd like to do! Still, amazing video. Youve just gained another sub for what it's worth 😊
@@PureNrGG haha thanks!
Good information.. been gluing various stuff for almost 30 years now… I always questioned the TH-cam gurus who took clamps off quick.. I always leave overnight and never had issue.. plus your point of well fitting joints is key.. my uneducated guess is pressure release from taking out of clamps or hands let’s glue gap increase.. there is info on gap strength and limits … again beyond what I can process.., but I never had a glue joint fail drying overnight.. looking forward to next test vid.. thank you .. enjoy the tiny human.. they’re the best .. u can’t clamp or glue then tho ..
She is definitely glued to me everywhere I go & those tiny fingers act as really strong clamps around my ears, too. haha. Thanks for watching!
Test finger joints to see if the geometry affects the 'strength' of the surrounding wood by enabling more natural wood flexibility near the joint.
I love the scientific approach you've brought to your channel. There are so many possibilities for things to test in the shop, I always look forward to what you'll test next!
Thanks for taking the time (and resources) to do that! You just answered questions that I've dwelled on countless times.
I love Titebond III.
However, I have believed - from my woodworking experience [I used to be a luthier] and am now a woodcraftsman - that it is weak unless it is left undisturbed for 24hrs. After then, it is an excellent bonding agent, and as you have shown, only 4hrs is necessary for reliable strength.
But good to have your scientific experiments to draw from, really appreciate it.
Great work, thanks.
Bravo, sir! This is an excellent approach to the scientific method--you control for the things you can, account for extremes in deviation, and publish your results in an easy to understand way while acknowledging constraints.
I'll definitely be reducing the clamping time between phases now that I understand this. I mostly make picture frames and smaller jointed items anyway. If something is clamped for 24+ hours, it's not a big deal, but I won't worry about the joints being too weak after 2-4 hours, so long as no additional stress is added in that time.
My assumption about the hand clamp vs the 30m clamp is that mechanical clamping forced most of the glue out and before it had enough time to set the wood sprung apart enough to leave microscopic gaps. I have no way to prove this though.
I agree. Feels like the most plausible reasoning. at the end of the day, any of us could disturb the 30min clamp project enough to weaken it. Best to clamp it longer till the glue strength really kicks in.
Saved me a pile of testing , thank you. I am also sharing because I think someone who takes the time to do testing is a valuable asset to any wood workers out there.
Appreciate you! 🙌
Titebond 3 cures more slowly than the other versions and Titebond 2 is the fastest cure. I glued thousands of glue line feet in red oak in the 90’s using TB2 because it allowed me to reuse my clamp rack sooner. I left it in the clamps for 30 minutes, then stacked the panels to cure 24 hours before thicknessing.
Several factors contributed to the success of my efforts. First was the joints were right off the tablesaw, not planed. The surfaces were decent but not perfect. I believe that this helped prevent a starved joint. The hand-planed joints in the video did not require high clamping pressure, and too much pressure can starve the joint.
Second factor is environmental. These were glued in Colorado where the air (and the hardwood) is dry, so moisture from the glue rapidly moves into the wood and the shop air, faster than in a more humid location.
My gluelines never failed and I regularly broke cutoffs to verify that the joints were stronger than the oak
I’m doing glue ups now in a 75% relative humidity shop with acclimated wood and Titebond 3. I leave the clamps on 12 hours minimum and wait another 12 before planing to prevent sink at the glue lines.
I think you're missing the 30 clamping point. After 30 minutes, most joints are ready for the clamps to be removed. That can be good since the clamping pressure can distort the wood and removing before complete glue setup allows the wood pieces to relax and flatten out.
Nice work! I have heard it said that a rub joint is plenty strong. It's not quite your clamp-free treatment, but that lore (and my experience) are consistent with your results.
Wow, what a good video.
As someone who has worked in destructive testing for years, your methods are pretty much as spot on as possible given the variables in material.
Now, next task (for me, at least) would be to determine the optimal amount of glue per square cm (sorry, am in Europe so we use metric) for the Cherry used.
Then compare that to less and more porous timbers.
I see a whole series of videos here!!
Agree, when releasing the clamps wood have a tendency to "swell" if I can put it that way. and well half dried glue the stretches and creates air pockets or pulls away from the micro bonds its made with the wood.
It would be nice to see the range of the results on the graph as well.
great video and even greater experiment and explanation, thank you very much for taking the time to do this 😃👍
Thorough with interesting results. Well done!
I have watched a couple of your videos now, and I like the common sense scientific approach you have for wood working and for testing wood working. Bonding materials together is an incredibly complicated science, but you got the broad strokes correct. Key take-aways 1) Bonds continue curing for a long time; 2) Just because the failure isn't in the bond, doesn't mean the bonded joint is as strong, 3) the feel of the joint doesn't indicate strength. Also, I'd say that what you are really showing is when it is "good enough". There are obviously too many variables to test for without a research grant, but I think this was a key thing to test and will serve as a good caution for impatient wood workers.
BTW the process you used for testing (isolating a single variable, testing a range of values, and definitively stating this may not hold for other materials) is great, especially in the age of TH-cam. In a real test, you would have needed significantly more samples (for material characterization they may do 100 tests or more). Also, while your test setup was very practical and very similar to a case that matters to wood workers, it is not very good for testing the bond. Being off from the bond one way or another will dramatically change the loading through the bond. You are also testing a complex loading, it isn't shear (sliding the two pieces along the bond) or tension (pulling them directly apart) or pure bending (which is really tension on one face and compression on the other). If you are interested, a 4 point bend test would be a "better" setup since you have consistent load between the inner two points, instead of a strong peak at the center.
All that being said, I have seen science journal articles that are less well done than this.
I found this video really interesting. As a side note, this "joint is stronger than the material" problem creates what we call in welding "stress risers," and we get the same results - cracking in the immediate vicinity of the weld but not the weld itself.
The real question is not how strong the joint is after clamping for 5 minutes, 30 minutes, etc. but how strong is the joint 24 hours after clamping for 5 minutes
Awesome detail! Thanks for exploring this topic. I can work more effectively now.
Good video.I too have done hand pressure clamps.Masking tape clamping and spring clamp and had good results.I definitely agree that a lot of creators go way overboard with clamping.I have made lots of edge grain cutting boards and used maybe 6 clamps and never had a fail
Thank you! Will save my clamps a lot of time! 😀