Building a CNC Mill/Router - Part 2
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- เผยแพร่เมื่อ 30 ก.ย. 2024
- Filling my new CNC mill/router with sand and epoxy resin to create epoxy granite, which will increase it's weight and vibration damping!
CNC Part 1: • Building a CNC Mill/Ro...
Old CNC router video: • My CNC Router... FINALLY
As a piano tech, I'd say you did a great job eliminating the frequencies that cause the most trouble. In pianos, that is.
Now he probably can reach all the gcode notes.
Haha, good point this would be an amazing piano now :D
You know, fiddling with settings might actually eliminate any leftover problem frequencies!
Maybe there are some sensors you can use to determine resonances, and software to compensate for it? If not, here's a great video idea :D
@@purvel : There are companies out there specialising in eliminating resonance in machinery... witchcraft?
Next up, how to build an aluminium CNC piano
I recommend to fill the legs with fine loose sand. It absorbs vibration much better
i think its gonna be hard to remove the epoxy sand mix
@@Supmah2007 the legs are still hollow.
Yea the whole point of using sand to dampen sound is that it converts vibrations into heat through friction, when you "stabilize" the sand with resin and remove the friction aspect, just creates a new medium for sound to travel through
Did you ram the sand down or just let is fall down?
@@TheRattleSnake3145 You want it loose
Those custom-fit sand funnels are incredibly satisfying
Your epoxy granite will have its own resonant frequency, because it is stiff. I think the whole point of the sand is that its lose and will move about and not resonate. Now you've just got 2 different materials with 2 different resonant frequencies, coupled together. Hopefully they overlap and still help a bit.
This is exactly the problem. You want sand as it has no resonance at all and is a great damper over basically all frequencies of interest. Also, sand fills the voids well but his cement will shrink a little as it sets and you lose the intimate sand to metal contact. All he has done is change the resonance by adding mass but has likely not introduced appreciable damping. I appreciate however that he has holes in the system and the sand would work it's way out eventually.
@@rob66181 Added mass of different resonant frequencies is almost guaranteed to dampen vibrations.
Epoxy granite wont resonate it behaves like a piece of stone
@@wizrom3046 Yes it does, most solid objects do. If you hang a rod of stone or concrete from a string, and tap it, it will ding. Thats it resonating.
@@ratgreen actually it doesnt. The epoxy is much less dense than the stone particles so the whole thing absorbs energy and is very low resonance.
Doesn't the fact sand moves help absorb vibrations? But won't the epoxy keep it from moving?
hard to say - the increased density of the epoxy + sand will dampen the vibration amplitude and frequency of resonance
on the other hand sand without epoxy could dissipate energy via friction
overall I would say increased density has a greater effect
While I never build a CNC or anything that needed to have low ringing/high vibration resilience.
My instinct would also be to use something that can move on its own and is only slightly coupled. Like Rubber or silicon.
But then again, every build I have seen so far uses resin and sand/gravel.
But all the other builds have their CNC standing on the ground or a very strong table. So I guess the feed are the biggest "problem".
Yeah the fact that the epoxy prevents dissipative losses means the sand is just ballast
Both affect the vibrations in this dynamic system. The increased mass increases the inertial force and the sand increases the damping effect since it is not perfectly bound by the epoxy (both of which increase resistance to motion).
i agree with you, to me thats one reason sound travels much longer distance in water then air
That Ballscrew is huge haha. Using huge ballscrews isn´t always good because it adds a lot of angular momentum to the axis, wich will impair acceleration a lot. 16mm Ballscrews are already way overkill for a hobby machine judging by the static and dynamic load they can take.
yeah lol i've assembled a like 4m axis on a cnc machine and it aint have ballscrews that big
yeah waaaayyy too big, if you want to reduce backlash you need a double nut as well, they preload the threads to provide greater axial stiffness.
@@muzzarobbo not entirely true; a ballscrew that uses "gothic arch type" ball tracks can be preloaded with a single nut. on a rolled screw this is the preferred method due to inconsistencies in the shape of the screw; a double nut on a rolled screw is more likely to bind up. if you want to use a double nut, the best thing would be to get a c5 or c3 precision ground ballscrew. the size of the ballscrew impacts acceleration but even a 60x60 mm 400 W servo should have no issues accelerating this ballscrew with 1 G of linear acceleration. the inertia of the system just needs to be close enough to the rotor inertia such that the servo control loop remains stable at those speeds
i thought 4 point contact ballscrews like precision ground ones are quite expensive compared to cheap rolled ones? i use a double nut on rolled ballscrew with no binding issues@@ikbendusan
Would loose sand dampen vibration better than the weight of the epoxy granite?
imo increased density due to epoxy added has a greater effect than friction within loose sand.
You're all going to give Tom a complex and his next video will be testing like 30 different materials for frequency and stiffness.
The mass of the sand probably has more of an effect on damping than the loose sand itself. Additionally, loose sand would end up finding ways to get out and would make a mess.
@@yetanotherdan This reminds me of the whole marble machine madness for those that know.
@@ChrisValin-w6o not enough mass
MY only real concern right now would be that this is a little top heavy. Cool idea for a design though!!
Perhaps stiffen the frame with framing lumber like 2 by 6 or 2 by 8?
It's generally considered best practice to mix the epoxy parts before you mix it with a filler. That way you can be assured of good mixing.
Well done! I did exactly the same on a custom build that I currently assemble.
Your problem is indeed the stand. The CNC should be heavy on the bottom and get lighter the higher you go. You have a very rigid machine now, on a flimsy undercariage. You will see how shaky it will become, once the machine is up and running and you do some highly dynamic stuff with repetitive direction changes, like boring or adaptive clearing. Maybe you have some possibility to attach the legs to the adjacent walls with some wooden spacers. This should fix it.
But in any case, it is a great build 👍
Well if you ever give up TH-cam, there’s hope as a percussionist
I'd assume the dampening properties of the sand are cancelled out (or atleast reduced) by the expoxy holding all the grains together. The sand cant absorb the frequencies by moving around.
Maybe diagonal steelwire or braces between the legs. It seems like you now have more weight on spaghetti legs. And I dont know what type of machine feet you have but stiff dampers could also maybe help further.
Good job! I think you'll find it helps a lot more than you think. Resonance or vibration is only part due to stiffness (lack of...), you also need to consider the accelerated mass. Doubling the tightly coupled mass of a beam lowers the resonance frequency, sure - but the important part is that the beam impact load moment of inertia goes up to a factor of mass increase squared. Doubling the mass means that the same impact force now gives four times lower beam displacement. This helps a lot on all vibrations and momentary impacts that are NOT perfectly synced to the resonance frequency. At (the now lower) resonance, the same amount of impact force has the same displacement as before though
You just described drum tuning in the most scientific way possible.
Excellent overview of the benefits related to increasing mass. It is my understanding that the stiffness of the overall system increases. I think he could have increased mass further if the mix was compacted in layers. The mixture didn't seem fluid enough to settle with just a few taps.
For future reference, a bit of heat will soften threadlocker.
Tip for pouring from containers like the ones your epoxy came in: hold the bottle sideways, so the hole in the handle is "eye to the sky" This way you dont get the typical glug glug that slows down pouring and makes it more dificult to be precise.
the sand-epoxy dough looks edible enough, wonder how that taste like
gritty
cockles on a cold wet stoney brit beach
Looks like kinetic sand one had as a child
It tastes like eating chips at the beach on a windy day
Probably tastes like cancer
Tom! As a percussionist, I highly recommend using some drum mutes/dampening pads! You can grab a couple of snare mutes that are essentially like little sticky gel pads and slap them on the outside of the extrusions. Or you can fill the inside of the legs with loose sand which should do a better job of absorbing those frequencies. OR you can even encase the bottoms of the legs in a little bit of silicone (mold a foot around them and put a slightly more resilient rubber pad on the bottom underneath the silicone mold perpendicular to the end of the extrusion and the silicone, and epoxy the two together). Any/all of the above can help a lot with dampening the ringing if you’re not already adequately satisfied with how it currently is. Hope this helps!!
Or Dynamat for car sound insulation on the legs might work.
The objective is to remove chatter:
Eliminating "ringing" created by tool cutting edges contacting the workpiece at a harmonic of the frames natural frequency is one reason to fill the extrusions.
Another reason is to increase the overall mass of the machine... this alone can be a significant improvement.
I guess that's why you don't see many portable Bridgeport mills! 😜
Really looking forward to the rest of the series; I don't think you are going to be disappointed with the finished machine.
It doesn’t sound the same at all! Sounds much better!
The fact it still rings may be attributed to the hollows that still exist in the corners of the aluminium extrusions.
Paving slabs, across the beam bottoms, heavy, stable and could be used as a shelf for stuff! Would probably benefit from bedding on closed cell foam/other stuff, and securing!
Good idea.
what a absolute waste of a $2000 piece of machinery.
I am guessing the Cnc wasnt as easy to build as expected
The narrow legs, in fact all of it could’ve been filled with leveling cement. It’s very liquid and smooth, and much nicer to work with than epoxy.
I'm thinking about using high strength concrete...
Ive used molten lead.
@@philiprogers5772 I'm too lazy to deal with epoxy. I can't imagine messing around with lead.
@@philiprogers5772 That's going to play havoc with his 3D printed funnels :)
@@-vermin- Lol, also I wonder if the expansion and contraction would cause deformities.
Maybe try to Wrap a Rubber mat or Rubber Tape around the legs? The Rubber could absorb the virbrations and also isolate the Sound or reduce the frequency. I guess even normal Tape would Help notacibly.
The biggest mistake was mixing sand with epoxy. Loose sand acts like a dumper, it does not move like a single weight, but the movement of grains relative to each other dampens vibrations. Moreover, loose sand fills the empty spaces more tightly. In fact, you had to print the ends of the profiles (which you did anyway), paste them on epoxy, and pour loose sand between them.
Now you just added masses to the profiles, which is of course positive, but not as good as it could be.
Epoxy-granite acts differently - the epoxy absorbs the energy as the vibration waves travel between the sand grains and the epoxy.
If I recall, New Yorkshire Workshop's CNC build featured concrete, so you're going in the right direction!
That was a great build !
Mate, the idea of using sand it’s that stays loose (dat absorb vibration better)
I made my farrier anvil stand and filled whit loose sand, that work perfectly
Its the principal on “dead blow hammers”
Use dry sand on the the vertical legs. its pretty much self compacting and should pour in like water if the sand it totally dry. iv had bags of kipn dried that were not dry before hahah
Where is part 3? I check back every week 😂
I'd bolt the entire thing to the ground or a concrete block, with rubber gasket between aluminium and concrete.
I'd also put lightly coupled (or gasketed) bracing between the middle of legs and the uprights, reducing the number of long lengths that can resonate.
Many likes the idea of lose sand, but I’m not sure how much that small amount of mass would dampen the high amplitudes of vibrations. If you look in the industry, dampening has never been used (as far as I know), only stiffening and mass in the body.
I think you are putting too much faith in the linear rails being straight, I would almost bet the extrusion is straighter reference edge. Even high quality rails are almost always bent from factory and you need to use the mounting screws to pull them in line.
Really you should be setting the axis flat relative to the table, followed by setting the ballscrew flat to the rails.
Unless you have checked them with a proper straight edge of course!
I feel like you're not taking this project as scientifically as the trebuchet. Small scale testing to prove concepts before a bunch of wasted manufacturing.
The natural frequncy of the central 2 beams in the bending mode is quite low still. You can help reduce ringing further by adding vertical (or triangular) support columns underneath the center 2 beams, supporting their centers from the floor. This should increase the lowest natural frequency of the center beams at least by a good amount (I am guessing 4 or 8 times), which should reduce ringing.
This only helps the up and down bending vibration mode though. To also reduce the in and out of plane bending vibration node you could add 3 short support beams in between the beams on the platform, supporting the centers of the beams from the side.
Loose sand absorbs vibration way better than epoxy sand combos.
That's what I was thinking: you don't see deadblow hammers with epoxied shot in them
Do you really need to rigidly mount the frame to the feet? Maybe adding some rubber to the mounting-points could dampen the vibrations traveling from the main frame into the base/legs.
Here is what’s happening: filling the cores increased the mass and lower the resonant frequency. But to dampen the vibrations, you need to dissipate that energy somehow and for that, you need loose sand. I think you’ll be fine, but you could try filling the legs with loose sand and compare them to see how it changes. I did this awhile back with some speakers stands I have. I filled one with some very dry, fine Masons sand and compared the sound by swapping stands with one that wasn’t filled. I didn’t expect any difference, but it really sounded significantly better. So, I don’t know if it would make a difference in machining quality but it does make a difference. If nothing else, maybe it will help to make it quieter when operating. You should also try to use some strips of sound dampening mat, like they use for car audio. You don’t need much, just a strip on each extrusion. Just be sure to put it where you’ll never need to remove it because it really sticks.
i thought the m in mill was a w and was spelled wii so i was thinking that he was gonna make his own wii sensor bar, but i still like this😅
Interesting that you filled up the rails with epoxy granite. I did something similar when I was putting together my own CNC router to cut down on the vibrations during milling.
Instead of just the rails though, I made a mold for the whole base of the CNC and poured a mix of 20% epoxy and 80% sand into it. And it worked well. I basically wrapped an aluminium frame in epoxy-granite for my CNC machine.
One thing you might want to think about is shaking out the air bubbles and gaps in the epoxy granite a bit more. I rigged up a DIY vibration table for this, attaching a cement vibrator to a plywood board, and let the mold vibrate for the entire curing time.
I'd think filling in the gaps in the aluminum grid structure on your CNC with epoxy granite would make the vibration dampening even better. Just my two cents from building my own CNC machine with epoxy granite for the past year.
Where can i see your build?
Made my CNC base out of structural concrete and i love it.😊
Do not constantly vibrate during the curing process this causes the sand to settle to the bottom of the mixture. This is a big no no when mixing regular cement. You can actually see it happen if you put a vibrator into the mixture and not by vibrating the entire structure. The mixture around the vibrator becomes watery if you leave the vibrator stationary.
I would have only seal the ends with epoxi-sand and just fill the rest with normal sand.
what about spray foam in the legs to deaden them?
I would suggest to further stiffen the lower structure (that can't be filled with sand), for example by simply introducing more cross beams or diagonal beams. This should greatly reduce vibrations in the system.
so, you skipped your CNC machine's leg day?
The theory behind EG is to use different size aggregate, sand - 10mm pebbles, this breaks down the vibration a lot faster, stops the vibration from travelling because of all the different size objects to go around
Hi Tim. I've been considering epoxy granite for my CNC build, however I strongly believe that the Sikaflex 290DC deck caulking that we use at work for cruise liner Teak decking will be a good alternative choice. My reasoning is down to how these dampening materials work; converting vibration into heat through friction. Epoxy granite alters and shifts the resonant frequencies within the system to longer wavelengths which are less intrusive than the higher "ringing" plain Aluminium produces. Sound dampening materials in audio applications tend to use dense flexible materials such as rubber or polyurethanes which are very good at converting vibration to heat. Sikaflex polyurethane caulks are single component and much more convenient than mixing up dry aggregates and epoxy, which is an attractive benefit.
It might be 2030 by the time this is finished.
yea, i´m also waiting for part 3 ...
How about filling the legs with lead shot?
The sand will help the most with the high frequencies represented by localized flexing of the walls. The lowest frequency modes represented by the whole thing going back and forth in bulk wont care as much about the epoxy fill; the high frequency modes would be the most annoying ones to deal with for the machining process though; there is a lot of energy injected into the system at your spindle rpm * number of cutting teeth; not really a whole lot in the lower audible range of a few 100hz where most of the leftover response seems to be. Thats just armchair philosophy though, don't have hands on experience. But it seems like a worthwhile upgrade to me.
Maybe adding strips of heavy rubber to the outside of the legs would dampen the vibration. Something like horse stall mats cut into strips and bolted to the extrusion?
maybe add between leg and main frame?
Appropriate Barry Mounts would be my first choice.
Your videos are like asmr for engineers ❤
Feeling like the sand should have been loose
I have done the same thing with my welded machine, but I compacted in the epoxy sand mix as I filled it and that made a noticeable difference.
One tube I had to fill sideways and could not compact, which resulted in a noticeably less uniformly and densely damped tube (you could hear the difference when you hit it at different positions).
This sounds a bit out there, but take some 3M double sided adhesive tape (the really thin stuff) and tape thin aluminium plate over every exposed t-slot, this makes them all closed sections. 3M adhesive tape is shockingly strong in sheer (if you choose the right one) and changing the open sections to closed wall sections increases the Torsional rigidity of the beams, the tape also gives some dampening. This is something Alexander Slocum speaks about in one of his lectures. He's the writer of "Precision Machine Design" - which is basically the machine design engineer's bible.
I think it's this lecture: th-cam.com/video/8rKrUsXiFOo/w-d-xo.htmlsi=mmLKntXZSzGy7-vk&t=700 (FOUND IT)
Wrap the legs with a rubber material
What a fitting video! Just yesterday I decided to fill the column of my milling machine to reduce vibration and increase weight. I used a product called "Durfill" by Durcrete which is a cement glue based engineering concrete for filling structures and building machine bases. It expands slightly when curing to fill gaps and self levels. It's less of a mess than dealing with epoxy resin.
You mean durafill?
@@NiclasGudmundsson no, I used Durfill from Durcrete, a German manufacturer of ultra high performance concrete.
@@Sven_Hein ahh thanks, I will have a look to see if I can find that here in sweden too. I'm having thoughts to make a concrete bottom part for my machine so I can have a built in coolant system.
I am going to repost my previous comment from the previous video since I believe it could cause problems in the future for you:
I am skeptical of that ball screw placement. Ideally, you'd want to position it in a location that wouldn't create torque on the gantry, which in a non-loaded situation would be in-between the two linear rails. You could also position it on the underside of the carriage in a spot that would oppose the torquing force produced during cutting.
With the seeming scale of the screw and rails I'm not too concerned about that - the torque isn't going to be huge and those rails and screw look rather overkill already (at least for this frame construction). Plus the reasonably large spacing of the rails and bearing blocks on each rail will help it deal with the lateral loads the torque can create. And as Putting the screw on the top does keep it out of the path of debris from use and out of the potential workspace of the machine... Will obviously depend on the quality of screw, rail, etc but I think this is an acceptable tradeoff for this design, I think its the way I'd do it if I chose to build with those extrusions to this scale (but I don't think I'd do that in the first place - my plan for a machine that fits my space well is currently steel C sections and square tube largely filled with epoxy granite - may not be a good welder (yet) but I can stick metal together that way and to me seems the best mix of easy, affordable and stiff frame).
cannot wait for part 3.... the structure is sturdy :)
Great video Tom! Getting rid of all that vibration is indeed very important 👍
Currently working on a cnc build as well with an extrusion based table/enclosure. To cut down on vibrations and to make the table much stiffer im attaching mdf panels to the sides of the table. Also contemplating using some rubber like gasketing or some sort of putty between the mdf and extrusion.
Regardless, stoked to see where this goes! Oh and also something worth checking out is services like jlcpcb, pcbway (pretty sure they do sponsorships) and rapid direct. If you have any weird brackets or mounts you wanna make, you can just shoot them some cad and some money and you'll get back freshly machined pieces.
One other idea, where you have linear rails, you could just get a slab of mic-6 and mount your linear rails to that. Mic-6 is usually pretty darn flat and not too expensive.
Anywho looking forward to the rest of your build!
I don't think adding weight to the bottom of the base will help that much, since the main problem, it looks like, it the frame itself flexing (very slightly, which is what the vibrations are). Like others have suggested, I'd definitely say finding a way to fill the legs would be a massive improvement. Whether that means changing the legs to be the square tubes so they're easier to fill, filling them with loose sand rather than the epoxy mixture so that it's easier to fill, or something else. I work in custom automation, and for machines with something like an ultrasonic welds on it, which exerts tons of pressure (literally) and vibrates in the range of kHz, so frame rigidity is very important, I would think it would be a strange design choice if one of our designers made a big stout gantry and mounted it on less stout legs.
There is always tradeoffs when designing such a machine. Take your gantry axis for example. You can use very low rails to increase rigidity but then often loose out on drive-stiffness by needing coupling over to the leadscrew (like you have). Alternative is using taller guiderails where the leadscrew can fit under and the coupling nut carrier can then interface directly with the axis for a stiffer drive position. In the end I do not know which is more rigid but I went for the second option on my machine based on simulations in the CAD.
I don’t like sand
Pretty sure a lot of resonance would be removed by bolting a sheet of MDF or similar to one of the sides of the base, since MDF is elastic it's a great vibration sink.
The stuff in the middle of the beams is not as stiff as the aluminum, and it's close to the neutral axis. It isn't moving much, so to do much vibration damping it would need to really efficiently damp any motion that did get to it. The loss tangent should be high at relevant frequencies. Maybe RTV would've been a better binder than epoxy for this application. Something soft and goopy, bare minimum to hold in the sand--it wouldn't be load-bearing no matter what you did, so might as well maximize dissipation.
In epoxy granite, the composite is load bearing and moreover in the good stuff the load paths are through the aggregate to such a high degree that its mechanical properties are more rock-like. That's hard to do. You need several aggregate sizes and powerful vibration to consolidate it.
And the ideal amount of binder.
I can't help but wonder if it would have been better to just have raw sand in there with no epoxy. There's not much that's less resonant than a bag of sand. Oh well, I'm sure it'll probably cut just fine regardless.
On a heavy machine you have other problems than ringing 😂 And if there should be some ringelingeling, there are tools like Input Shaper.
I think there’s a making of a drummer in you Tim!
Like you said, you can always add weight to the base, and you can also make a dampener on top of the gantry for specific possible problematic resonant frequencies. Like they do in tall sky scrapers.
There is 4 ways to get rid of vibrations mechanically.
1)Dumping vibrations
Vibrations partially turns into heat or another energy form. Filling with sand to body and adding rubber foots includes this approach.
2) Adding or substracting mass
3) Adding spring element (with dumping element)
Firstly calculating (or FEA) the natural frequency helps a lot in the begining. Then you'll find some natural frequencies which is harmful to work with these frequencies. Accelerations of your cnc is limited by natural frequencies of machine's body structure.
If accelerations matches with your cnc you have to move away these frequencies with adjusting accelerations, adding mass, spring or dumping elements can be added "with calculations".
4) Transmitting vibrations to more rigid mass
Fixing the cnc to the floor helps to get rid of the vibrations because you will change the natural frequencies of the body.
Bonus: Eleminating vibrations with stepper or servo motors and creating counter frequencies is the solution. Open loop (like input shaping) or closed loop systems available. Try use "klipper" with cnc for input shaping. (An accelerometer will help you to measure frequencies)
6:53
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Buddy, you're a boy, make a big noise
Playing in the street, gonna be a big man someday
You got mud on your face, you big disgrace
Kicking your can all over the place, singin'
We will, we will rock you
We will, we will rock you
I thought the reason for the sand was to bring down the centre of mass, and to make it heavier, so it wouldn't move. Dampening resonance might work aswell, but i don't know if this is the best way. I saw people hang lifting weights on steel wires on the bottom of it to damped vibrations.. the idea is that you have a dampening weight on a string, that can move freely and vibrate.
I really love your approach! But .. I would go for High-density polyurethane foam to create a sturdy base, and reduce the weight. I'm no scientist or expert, but this is what came to my mind. Maybe it won't win from the sand / epoxy mix. Another way to go, but ends op very heavy is to fill the profile with concrete. As this is not flexible, it could crack, so I think this is eventually a no-go. Keep up the good work Tom!
Listening to the internet... My cnc machine stand same issue, used some gell blocks and some sound deadening foam/foil stick on stuff and job done. cost me 40 quid and took ten mins to do
Could you not just pour raw sand in the vertical legs? And, for more rigidity, have bolts go all the way through the extrusions?? I have built a similar machine with 2 inch extrusions with no sand fill. It is accurate +/- .005".
Don't want to be negative but 8:40 really summarized why people are questioning this. A HUGE lead screw, big extrusions, filled with sand/epoxy and tested with a hammer in the very unscientific "ring test." 😂 Seriously. Build it and see how it performs before over "engineering" solutions to problems that might not even exist.
Try steel or lead shot plus loose dried sand in the base. This should give you an acoustically dead stand, and make the tool bottom heavy. Right now you are top heavy and that will amplify any vibrations. You may also want to replace the uprights with square 80x80s. They will be easier to fill and give you a bit more contact area and stability at the corners.
Lastly, you may want to use additional angle braces or plates to increase the rigidity of your extrusion joints
While the way you mixed the epoxy was a great idea, I wonder if it would have been easier (and maybe cheaper) to fill the legs with bonded sand like Petrobond or even Kinetic Sand. There are also a few different kinds of casting sand (Sodium silicate sand) that can be poured easily and then cured to a "hardened state" with the addition of CO2.
As for the legs, I think it is less about the weight and more about the long, hollow surfaces that allow for vibration. May want to look at car-deadening mats (like Dynamat) and paints (like Spectrum's Liquid Sound Deadner) that could be added to help lessen resonance.
Sorry to say so but all you did was increasing the weight (what helps) but you wanted something to absorb the resonance and not another solid that's having its own frequency. The result is within expectation. Next time you could either use sand without epoxy, or a soft, damping material like a 2K PUR filler. And, btw, use automatic connectors for item profiles. That's a big help
Failed designed. Even if you replaced extrusions with solid steel, youll have the same problem.
The bed and motor need contact with a heavy and dense mass.
Youll be stuck cutting metals at 0.01 mm fpt.
2 posts for the motor, connected to horizontal posts with no direct underlying support 🤦♂if the goal was to create bell, this is perfect
You can fill the smaller areas of extrusions by loading the epoxy granite into refillable caulking cartridges and pressure/squeezing it into the extrusion. If you want more rigidity, you can use steel rebar implanted into the epoxy granite.
Print spacers in TPU to put between the 8080 extrusions and the legs to help blocking the resonance
Judging from the Bambu A1 printer initialization sequence prior to printing, it sounds as if they fixed it in software by sweeping the head through different frequencies and measuring the vibration. Do folk do this with CNC machines?
By epoxying the sand you took away the physical property that makes it dampening in the first place...
Sand moving under vibration is what dissipates the energy.
You didn't remove any ringing, you just added mass and so lowered its frequency.
I'm curious as to why you elected to make the legs so high - obviously I can't see if they are resting on something that raises it more, but I would have thought that shorter legs, a lower stand would have been more rigid. Also, the excess material could make a more supportive structure. Lastly, I would be tempted to put triangulation gussets in to prevent pantograph movement. Still, a very nice job, and certainly will be following!
there's gotta be some kind of convoluted nonsense you can do to reduce the ringing, or it's impact, some more. Maybe you can stick a transducer on it, build a calibrated striker device, and record the ringing, then get the spectrum of that ring, and apply a filter in the motion system to avoid exciting those frequencies? Or maybe adding some unnecessary brackets between members, with some dampening to dissipate and consume the ringing. My first thought was regular 90 degree brackets but you put rubber sheeting under them; but you might be able to just bridge the longways beams with 3D printed "bracing", and the plastic itself might serve as a damper
I'm no CNC expert but you should/could just add some diagonal braces from the sand filled bed to the legs, one on the short end from 1/2 way along the cross bar down to one of the legs, and maybe pairs on the longer sides, that will increase the resonant frequency significantly hopefully way above that of the steppers in motion. I wonder if you could even brace the two centre beams at 45 down to the end or side leg cross brace rails....(move them up to suit and don't fixate on keeping the sides and ends at the same height like you have)
Blasting garnet is MUCH denser than beach sand. I think the filler material should be loose rather than bound for best vibration suppression. It is important to have good coupling from beam to filler.
If you are not too committed. Moving the ball screw between or below the guide rails will help eliminate racking of the tool head. Your current design has cutting forces being resisted by the highly leveraged ball screw, encouraging racking..
Following! :) Your videos are always top quality. I'm going to make a CNC lathe with filled welded tubes (80x80x5mm steel) but i'm thinking about using pure dry sand due to the huge epoxy cost. I'm wondering if there's much difference between dry sand vs epoxy-glued sand.
If you need to reduce vibrations then you just need more mass. So you could create a lower shelf and just add weight.
I wonder if using water-proofing mix would be better than using epoxy granite. That mix has rubber in it which is excellent for absorbing vibrations. Epoxy granite makes the whole structure more rigid but I wonder if it really does anything to absorb vibrations. You could also use cement mixed with plasticiser but that may corrode the aluminium extrusions.
I built my CNC 8 years ago and it works perfectly as a CNC and because i didn't fill it with sand it might make a bad "Bell", But who cares i wanted a good CNC, Not a Bell. It also doesn't Fly or get me cold drinks.
You have to ask yourself a few questions if you want to go damping resonances. First one is which resonance will be a problem when running the machine. Next one is which mode of vibration were you hoping to dampen and will the method you chose do that. Increasing the mass will lower certain frequencies but to dampen a mode you have to actually get the vibration into the dampening material. Your structure has many modes of vibration, only a few will be dampened, many will just be at a lower frequency with more modes (higher order) at higher frequencies. Maybe a cad model will show you the frequencies if it can do modal analysis. Lowering some structural frequencies will likely bring unwanted modes down into your are of operation although it may also make some problem frequencies move down into a state where they aren’t a problem.
working with high end CNC machines myself, from manufacturers such as DMG Mori and Mazak, you will find that rigidity comes with mass, as well as how that mass is suspended. High end machines have huge iron castings which weigh literal tons, then the machine is levelled with specialist kit and it gets bolted to the concrete floor. The floor becomes part of the machines mass. If you didnt bolt the machine to the floor, vibrations would cause it to move over time, and your parts will be inconsistent, have poor finishes and just generally would not be good for the machine. Its the same sort of idea when youre machining hard metals such as inconel, monel, a lot of types of steel, titanium etc. if you have the material on a fixture high above the machines table with little support under the fixture, you get too much vibrations which will cause excessive too wear/damage, poor surface finish and so on, hence why when you machine these marteials, its best to try and make it one with the machine (bolt direct to table)
anyway rant over haha, what i would do if you could is make the legs as solid as possible, and bolt them to the floor. the difference will be huge. Many people end up welding something out of steel box section or I-beam extrusion, however if you dont have the resources for welding you could us large bolts (lots of them) and it will work well still
If you end up scrapping the structure, those aluminium extrusions have increased 10-fold in value at the local scrap merchant!!!!
Maybe inserting rubber/elastic "cushins" between the bed and the legs could help isolating them from each other? Of course that means another cumbersome disassembly and reassembly... But if you still decide to do it, don't forget the screws connecting the two halves together would also need some mini-cushins!
yeah, aluminium has a tendency to vibrate in unpredictable ways. I never understood the reason as to why. Steel for example is much more predictable. Predictable as in motion filtering algorithms are much more effective on steel framed motion systems than compared to aluminium. Wood is unironically excellent too in many ways. Maybe some wooden struts on the legs and semi load bearing walls around the top (Similar to something like the shapoko nomad).
I'd love to see the analytical 3D motion graphs of an accelerometer mounted to the 'head'. Klipper style with the different motion filtering algorithms. Maybe get the axes up and running and take some baseline readings, albeit with sand already and then add some wooden struts or side walls etc. and show the difference
If all you really care about is the "ringing"... for noise levels... or resonate frequencies... I'd say you could fill the legs with simple cotton balls or some kind of fiberous insulation. People who build skateboard ramps always glue sleeping bags or blankets to the underside of the skateboard ramps so that when the skaters ride on the ramps, the sound is "dead" and not like riding a skateboard inside an acoustic guitar.