Rotational Molding Tips And Tricks
ฝัง
- เผยแพร่เมื่อ 7 ก.ค. 2024
- You can use molds designed for casting solid resin parts to rotocast hollow parts.
Such molds are usually heavier than the blanket and mother molds used for rotation casting. So the trick is to make a cradle that mounts them on a rotational casting machine so that they are carefully balanced. You also need a quick way to close the pour spout and lock the mold into place for rotation. In this video I build a cradle and demonstrate its use.
Once the mold is secure on the machine you must cast the resin into the mold using just enough resin to coat the surface of the mold. I usually use 3 small shots of resin to cast the part. If you try to cast the part in one heavy shot the resin will pool inside the mold and cure in a big lump resulting in a failed casting.
I put one shot of resin in the mold and cut open the resulting casting to show the evenly coated walls. I also show how the resin flows away from the high spots inside the mold. This creates weak spots in the mold and is also why you need multiple layers of resin to complete the casting.
In making hollow castings it is frequently necessary to pre-paint the mold to make sure that you don't catch bubbles in the finer details of the mold. That is because the rotation forces are not strong enough to push resin into those areas.
Here is a list of suppliers for the rubber, resins and waxes I use in my videos:
www.dropbox.com/s/kz6mhmf7v5v...
Do you have a project to suggest for the channel?
Here’s a .pdf with everything you need to know:
www.dropbox.com/s/pjb0l6fr7zj...
TIME STAMPS
00:00 Using a mold made for solid casting to hollow cast parts
00:25 Balancing the mold in a cradle designed to hold it on the machine.
03:54 Mixing the resin and adding pigment to color it.
04:44 Pouring the first shot into the mold and rotating it.
06:17 Opening the mold to evaluate the “clean-out” casting.
07:41 Cutting the casting open allows you to see if the shot volume was correct.
08:32 Using a light lets you set the thin spots in the mold.
11:05 Pre-painting the mold to eliminate bubbles.
12:50 Pouring the first of three shots into the mold.
15:12 Removing the mold from the machine and checking out the casting!
16:52 Close up inspection of the parting lines and flaws in the casting.
19:10 Thanks for watching! - แนวปฏิบัติและการใช้ชีวิต
This video suffered audio problems when it was uploaded. It’s fixed now and should be working fine. Thanks to everyone who alerted me to the issues.
Who's ready to watch it a second time? Me, that's who. 😃
Thanks for the fix, Robert.
Thanks for watching twice!
It's not centrifugal force that pushes the resin into all the crevices, it's the surface tension of the resin in it's liquid state. Getting it to spread evenly over the entire internal surface is the trick, and the only way of ensuring that is to keep the rotation going sufficiently long enough for the resin to set evenly along all surfaces by continually rotating the mould long enough for it to set.
Surface tension is why I spray alcohol in my soap molds to catch all the details.
"The Witness Cup" sounds like a Humphrey Bogart movie.
😂
Bob, this was really a great teaching video. What I like about you is that you don’t just make a blanket statement. You go the extra step and prove your point. As with the speed of the rotation device. Cutting young “David” in half proved your point that it’s not speed but slow and consistent coating of the hollow mold. Good job!
Yeah Richard, I have learned so much by cutting open my castings. It’s painful to potentially destroy a casting but it’s also very informative for future work.
Another great video, Bob! I appreciate that you continue to show “advanced” techniques and allows us (the audience) to grow with you. It might be worth it for newer viewers to mention you’ve covered building rotational mold frames on the channel before. Maybe even reference those videos. See you soon!
Yes, I should have pointed out that my rotation videos are in a playlist.
You make it worth watching Bob. Another great video
Glad you enjoyed it! Thanks John.
Super good that you are putting time stamps into your videos. =) With those we can directly rewatch the parts where the audio was not working. 👍
Lovely video.
Yes, I find myself using timestamps a lot while watching people’s videos. Skip to the good parts!
I haven't even finished the video and learned so much! You've addressed how to fix issues I've just learned to identify and I imagine you've just saved me a great deal time, effort and materials!
Thank you so much for your incredible content!
Special effects to make a point!
I love your editing. Especially how you maintain your flow of narration through splices and sped up sections
Thanks Jonathan, glad you like it! It's always a challenge to compress hours of work into a few minutes of video.
Bravo!!!! I am intrigued and fascinated
Great video 👍
That's look awesome as a nightlight.
Informational gold as always, thank you for reposting this video.
sir ur works
awesome
Thank you . Congratulations
thank video
extremely thorough and concise, masterful tutorial.
I really enjoy your teaching style! Great video!
Thanks Mike!
Wonderful stuff, thanks.
I didn’t answer your question before I set the first flawed video to private. The orange and white striped tool on the board behind me is my clicker clacker. I have a Zoom sound recorder and anywhere from 1 to 3 cameras running in each scene so I use the clicker to sync the audio tracks. It’s just made out of one by twos and I paint it so that when I set it down in my shop I can find it. Otherwise it blends in with all the other pieces of scrap wood laying around!
@@RobertTolone thank you. 🙂
As someone getting into mold making, thank you! Your videos have been an immense help :)
So happy you find them useful!
Thanks Robert, As always this is a super tutorial. Each week i'm waiting for your new episode. I'm addict. Hugs!!
Thanks Melo!
You're always so delightful to watch, I hope many more people will find you in their recommended section. :)
Very glad you enjoy my videos. Thanks for watching!
I'm not sure this method would ever come into play in my shop with the "stuff" I make Robert but it was educational. At least if I do have a need to use rotational molding I have a reference to look at. Cheers
Sounds great now =)
Much better😀
Weird that the file corrupted on upload. It was fine on my computer. 😳🤪
@@RobertTolone I wondered how something so glaring could get passed your editing.
@@annekabrimhall1059 Glaring errors have been known to slip past me on several thousand occasions. But in this case it was not my fault. Something happened in the upload. I checked all the settings and did everything that I usually do but the world is not a perfect place and once in a while it kicks you in the derrière.
This is interesting, Just started watching your videos. I'm an amateur caster that makes occaisional parts for models I make. I want to make soft rubber tires for some 1/25 truck models. I have tires from suppliers but they aren't in business anymore, so I want to remake the few I have for future models. Just trying to figure out what the suppliers I got the tires from made them with. It's a flat black soft rubber, the tires are solid.
It’s very hard to say what the original tires were made from. You could make them out of either silicone or urethane rubber pigmented black. Just be aware that casting rubber into rubber requires that the materials are compatible and that you use a good release agent.
Hi Bob, great content as always. Quick question, is it ok to pour resin on cured resin, I've never had that much success with my PU as it seems not to want to bond to itself once set (unlike silicone). Cheers.
The urethane resins I use always bond to themselves just fine. Be sure that your A/B ratio mix is perfect. Otherwise you could have some sweating of uncured resin, etc.
hey robert, i have been bingewatching your videos, and have for a long time wanted to try my hands with casting, but i have found it hard to figure out what i need to begin, and what would just make things easier. do you have any advice on something like a starter kit?
Well, I guess the minimum you need is silicone rubber, urethane resin, mixing cups and stir sticks, a scale, an XActo or other sharp knife, rubber bands that fit your molds, gloves, paper towels and acetone for clean up. The list of what you will want if you really get into mold making is much longer.
Imagine putting a light inside after just the first shot! That could be interesting
The casting that I lit up had only one shot. The second and third shots coat more evenly because the resin bonds to itself better than it sticks to the rubber.
I was thinking more as a nightlight sort of novelty
Cant believe how nice that rotocast came out. I built a rotocast unit some years ago, and it never worked properly but I can resolve every issue I had by watching your videos. Would lightly coating the inside of the mold with talcum powder help minimize the air bubbles? Or, would that adversely affect the finish of the cast?
I’ve never been a fan of the talcum powder method. But a lot of people swear by it. All you can do is give it a try and see if it works for you.
What kind of clay do you recommend for a clean and polished end result? I’ve tried air dry clay and some basic sculpting clay (not good with either) but was curious on your thoughts on it.
Generally speaking, harder clay is easier to polish than soft ones. Something like a very hard sulphur-free Chavant clay. Or Monster clay. Professional clays will usually give you a better result than the craft store varieties. Although I have to admit, people do amazing things with Sculpey.
I've heard mention in previous videos about filling holes but I haven't seen it done. Did I miss it or is that something you could make a video on?
I've tried filling before but it never looks right. I used to loose a lot of pieces to holes but I fixed my mold and don't get them as often.
I hate to clean parting lines and I hate to fill holes. If I have only a couple of small holes I will fill them, usually with epoxy clay, but if there are a lot of flaws in the casting it’s faster just to make a new one.
@@RobertTolone ok thank you. Was just hoping to learn how. Have a great day. 🙂
Thank you for all the great information! So helpful! How do you deal with the little bubble holes? Would something like Testors modeling putty work? Also, have you ever had problems with the layers of resin delaminating?
I mostly use epoxy putty for large holes and the modeling putty they sell for plastic kits for small ones. Bondo is also good. You can also use the urethane resin itself, or baking soda and superglue. Or make urethane resin dust with sandpaper and mix with 5-minute epoxy. As you can see, just about any filler works just fine.
No, the resin bonds to itself really well.
@@RobertTolone Cool! Thank you!
You might've mentioned this before, but do you need to wait for previous coats to fully cure before adding subsequent ones, or do they just need to gel?
Each coat just needs to gel enough so it won’t peel off the sides of the mold when the next pour is added. Your witness cup will tell you when it’s ready.
Hi Robert. That as great! I once made a mold/cast of Popeye sculpture for a client and had a night are with thin spots, though that was without a rotating rig. I'm definitely gonna make one next time.
Wondering have you done any casting with metal powder effect fillers?
Also wondering, as that wax version shrunk and warped, does that usually happen when they make wax casts for bronze metal lost wax casting? Maybe it's a different wax or something? 🤔
I have done some cold cast bronze work but not very often. I find that the hardest part is cleaning the castings to make the surface look good. For instance extremely hard to fill holes and get them to blend in.
@@RobertTolone ah yes, I had similar issues when I tried it. Though I don't have a pressure pot set up. Wonder if a bicycle pump would work in a pressure pot? Possibly too weak.
@@mickybetts7957 Also very hard to pump up a pressure pot quickly enough with a bike pump. The resin would set up long before you got it up to pressure.
Seems like spinning it fast might be good to get it in some smaller crevices of the mold. Then slow it back down after a minute or so.
Maybe it would, I've never tried it. You would have to build a rotation machine and cradle that could withstand the high RPMs. And you would not want to get your hands anywhere near it. In my motorized rotation days I was extremely careful to not get my hands caught between the spinning frames of the machine.
@@RobertTolone of yeah for sure. I don't really even know how fast it would need to spin, probably depends on the mold.
But at the same time, if the mold has bits that small, would probably be a real pain to cast anyway
Heey a question about how I can demold a concrete statue out of a shore 40 silicone mold. It is a one piece mold but it’s really hard to demold, do you have some advice? Thanks!
It's a very firm Shore rubber. For concrete casting I would switch to a urethane rubber mold and make sure it's soft enough to flex off the casting.
Great content Bob!! I have been binge watching for days. I do have what I think might be a fun/challenging design I created to try to cast. How can I get the design to you to evaulate? The design is the model in my icon here. Thanks in advance. -Joseph
Reach me at roberttolone@yahoo.com
Hi Robert! How would fix the bubble issue with a seamless glove mold? Where I can’t just open up the mold along the seams and brush resin in spots I need it?
That is one of the problems with glove molds and why I almost never make them. Glove molds are perfect for certain objects but I find they don’t work very often for me.
@@RobertTolone gracias! You’re the man!
You mentioned how heavy the mold is, how would you build a rotocaster for a mold that weighs almost 20 pounds when all the resin layers are poured in? Thank you
This machine would easily spin 20 pounds:
th-cam.com/video/0IsWzmWj-5o/w-d-xo.html
It's not the weight, it's the balancing the load over the centers of rotation. If the mold is well balanced it will spin effortlessly with no stress on you or the machine.
@@RobertTolone thank you!
Amazing video. Thank you ! I am trying to roto mold a small stool of L30cm x W30cm x H40cm with four legs. do you think it's possible with your metod ? I believe it would have to have at least 2 batches of plastic. is it possible to rip open the first layer and pour the 2nd batch ? Have a nice day and stay safe.
The closer your object is to the shape of a ball the more likely you are to be successful roto casting it. Objects with lots of long thin parts like a stool are not very good candidates for Roto casting. It would be possible to cast the separate parts individually but even then the long thin parts like legs are difficult to cast with rotation.
@@RobertTolone Thank you Robert for your advice. I will still try to rotomold it anyway just to test out since it has some chunky legs, do you think cutting a hole after the 1st batch of resin and pour the 2nd would work?. If this fails I will just make it solid resin, I was trying to find a solution to save some material. Thank you.
@@keunartist Yes, you have to cut open the plug hole to pour resin in successive batches.
WHAT SILICONE HARDNESS PRODUCES THE CLEANEST MOLD LINES? SOFT OR HARD?
Any hardness of rubber can produce near invisible parting lines. More important than the Shore of the rubber is how you cut the mold and how you hold the mold closed. Technique matters more than the materials.
@@RobertTolone Thank you! You're an inspiration.
Hey Robert! Do you happen to help amateurs like myself make a complicated mold. If so what would be the best way to contact you? Thank for the help and live the channel.
Reach me at roberttolone@yahoo.com
@@RobertTolone awesome.... thank you!
Surprised to see an absence of suction defects with an unvented rigid cast.
I’m not sure what suction defects are. I always punch a small slit into the pouring area with an Xacto blade but the air rushes out, not in. That is because the curing resin heats the air inside the cavity and causes it to expand.
@@RobertTolone Some of the air usually escapes as the resin warms, before a full seal is developed. As the piece cools to room temperature with a seal the escaped air can show in indented areas, mostly broad flats. I missed the knife slit.
What is your email ?
roberttolone@yahoo.com