Rubber for molds

Got a question about techniques, materials or other aspects of physically building a model? This is the place to ask.

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Kenny
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Post by Kenny » Fri Nov 10, 2006 12:44 am

Help me down under.

I want to try casting parts with proper RTV molds and resins but can not find any supplier of a proper grade for model making. Has anyone in New Zealand or Australia know of a source of any of the recommended products or a Us/Europe supplier that can send Overseas???
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Post by OdysseySlipways » Wed Nov 22, 2006 10:24 pm

Sorry kem can't help none.



I started out using Alumilite quick set rubber, then there HSII & III. I was using their slow set resin until they stop selling it, then I went to Polytek until their rubber bonded to one of my masters, then I went to Smooth-On. i would run to their Easton building about every 3 weeks, sometimes 2 weeks to buy more resin, rubber, and release spray. one of the last times I was there, I was asked if i wanted a desk and an office (couldn't tell if she was joking with me or not - still don't know).

I currently use Smooth Cast 321 and use both Mold Max 10 and 40. I think the release spray is Mann Ease 2300
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Post by pyxl » Sat Feb 03, 2007 2:36 pm

Anybody ever use any products from Hyperlast (used to be part of Synair)...namely SilMold?

I've used their "pour-a-kast" product..but not the mold material.

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Post by PetarB » Mon Feb 05, 2007 7:34 am

Kenny wrote:Help me down under.

I want to try casting parts with proper RTV molds and resins but can not find any supplier of a proper grade for model making. Has anyone in New Zealand or Australia know of a source of any of the recommended products or a Us/Europe supplier that can send Overseas???
try www.meury.com.au

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Post by Pandaphil » Wed Mar 05, 2008 11:09 am

A dumb question, but any suggestions on a good starter set that doesn't cost an arm and a leg? I'm not planning to go into production, just want to make 2-3 copies of a couple of a few small model parts.
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Post by OdysseySlipways » Wed Mar 05, 2008 11:49 am

i am not familure with all of their products, so i would say just email them and ask them about a started set and to be sure to get a rubber that doesn't require a de-gassing/vaccum chamber.
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Post by Sparky » Wed Mar 05, 2008 11:33 pm

check out <A HREF="http://www.tapplastics.com/" target="_blank">TAP</A> plastics' how to video they have a method that you can use to degas without a pump. It is not conducive to making multiple molds at one time, and requires a stable protected area in which to 'pour' the mold.
Last edited by Sparky on Thu Mar 06, 2008 10:10 am, edited 1 time in total.
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Post by OdysseySlipways » Wed Mar 05, 2008 11:43 pm

:? where exactly are you looking for this "How To" video? is it under the books and DVDs?

and is that also refering to the "It is not conducive to making multiple molds at one time, and requires a stable protected area to in which to 'pour' the mold" coment?
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Post by Umi_Ryuzuki » Thu Mar 06, 2008 1:05 am

Sparky wrote:check out <A HREF="http://www.tapplastics.com/" target="_blank">TAP</A> plastics' how to video they have a method that you can use to degas without a pump. It is not conducive to making multiple molds at one time, and requires a stable protected area to in which to 'pour' the mold.
What I find entertaining is that the video states that the vacuum method should be maintained for 6-7 minutes. Their hardener doesn't allow that kind of working time. :roll: Which is why I stopped using tap RTV
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Post by Sparky » Thu Mar 06, 2008 10:09 am

The bombs away method is sensitive to slight air movement. It's harder to make a bunch of molds since you'd have to have several areas where you could set up the cup [high] above the mold.

If you mix one big batch of RTV for multiple molds then you have to carefully divide it up and if one mold starts to over flow you have to be able to get to it without disturbing nearby RTV streams. It can be done but I bet more RTV will be spilled or lost, it would be a big headache to juggle it all. In the end I'm sure one would agree the bombs away method is not conducive to making multiple molds from one batch of mixed RTV, unless you have a great expanse of work area.

<A HREF="http://www.tapplastics.com/info/video.php?" target="_blank">TAP Instructional Videos</A>

PM me if you have limited computer access and or internet access. Or catch me during the how to demos at wonderfest.
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Post by Sparky » Thu Mar 06, 2008 10:17 am

Umi_Ryuzuki wrote: What I find entertaining is that the video states that the vacuum method should be maintained for 6-7 minutes. Their hardener doesn't allow that kind of working time. :roll: Which is why I stopped using tap RTV
Well they also suggest using urethane RTV with casting urethane resin, <I> you will need is mold release</I> No you will need an aspirin and blood pressure medicine. Urethane RTV is good for casting cement, see the second link in my sig line. Use silicone RTV for casting urethane resins and save your self. I keep an example of this for my casting demo.

There are some good things in their how to videos. And the videos are there for free. Not many other company's put any videos up. I heard for Jack Wendt that the Smooth-on video you have buy is ok, so probably has the same issues as the TAP videos. I.E. some of the info is not good for beginners, and most casters wouldn't use the technique in everyday production casting.
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Post by OdysseySlipways » Thu Mar 06, 2008 11:58 am

oh, they show you that if you let the rubber trickle from a mixing cup into the form, it will take care of the air bubble thing? maybe with their stuff it might.

since i have been using a vac pump it makes a world of difference. with that, i can do around 10 small molds at a shot (i think the most i did was about 20 at one time).

as for prepping the mold with release prior to casting with it - i have always used it.
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Post by Sparky » Thu Mar 06, 2008 12:11 pm

Cyber Sith, Ed was making his own ammunition cans for a 1:72 tank and he was having such trouble he was ready to toss it in (this was his first or second time molding and casting) The amount of mold release needed was blowing away parts of the amo can (the lip of the lid from the open can is very tiny).
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The amount of mold release needed for urethane to urethane casting is magnitudes larger than silicone to urethane castings. For beginners i wouldn't recommend compounding the learning curve with mold release.

I agree that once you're into production casting its worth it to get good at using mold release (extends mold life and enhances what you can mold).
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Post by OdysseySlipways » Thu Mar 06, 2008 2:25 pm

i don't think that using a release agent is anything complicated. it's just a matter of giving a slight spray/mist on/into the mold prior to putting the mold halves together.

puting barrier on the first half of the mold prior to pouring the second mold half can be more troublesome.
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Post by Antenociti » Wed Aug 13, 2008 4:42 pm

OdysseySlipways wrote:i don't think that using a release agent is anything complicated. it's just a matter of giving a slight spray/mist on/into the mold prior to putting the mold halves together.

puting barrier on the first half of the mold prior to pouring the second mold half can be more troublesome.
Have to agree with Odyssey - whats complicated about using mould release... we use it when casting 1:100 and 1:120 vehicle parts without any issues at all, and some of those parts are smaller than that linked to... or are we discussing different things?

The TAP videos are excellent imo - they're free and well produced, far better than most other online resources.

Best silicone we have ever used is Viscalo 22, its "oil free" and almost self-degassing it is so thin and fluid. We get around 75-150% more casts out of it with resin than other silicones before it starts to degrade and go a bit hard on the edges.

Fabulous stuff though it costs about 20-30% more than most other silicones, i've never had a bubble in a mould since we started using it (we do pressure-cast our moulds mind you).

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Post by Squall67584 » Fri Sep 04, 2009 5:54 pm

I'm wanting to make a mold of several different greeblies but want them to be in the same mold to save on costs. Mainly they're bits and pieces from a Revell Venator, mainly one sidewall and an engine nozzle, and a few other round bits about the size of a quarter. How close can the parts be and still be able to cast and remove them without damaging the mold?
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Post by Ziz » Thu Apr 08, 2010 5:01 pm

mold box question - as long as it's sealed along the joints, does it matter what you make it out of? I have a bunch of heavy corrugated cardboard boxes from BJ's sitting here that I could use to make custom surrounds for parts I want to cast. Will the rubber soak into and stick to the cardboard to the point that I won't be able to remove it?
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Post by Johnnycrash » Thu Apr 08, 2010 5:22 pm

Cardboard is fine. The coated stuff (like cereal boxes) is better. Some of the surface paper may come off, and stick to the mold. To reduce that, just spray it with mold release, or grease it up with Vaseline. Or, you could line the box with white printer laser paper. I use old paper (print outs that are no longer needed) as mold box extensions. When I evacuate the rubber, it expands big time. :) And most of the time, the paper doesn't stick to the rubber.
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Post by nkuzmik » Wed Aug 31, 2011 6:16 pm

What about aluminum?

I'm looking to make a bunch of small bases for various bits and my original plan was to have a friend turn a mold out of a blank that I have laying around. Simple shape, a short, wide cone with a wire to support various bits.

Any thoughts? Specifically, what materials.
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Post by Joseph Osborn » Wed Aug 31, 2011 7:21 pm

nkuzmik wrote:What about aluminum?

I'm looking to make a bunch of small bases for various bits and my original plan was to have a friend turn a mold out of a blank that I have laying around. Simple shape, a short, wide cone with a wire to support various bits.

Any thoughts? Specifically, what materials.
What exactly is the question? Are you unsure of what type of rubber to use with an aluminum master? The answer to that is "just about any silicone rubber you want-- the cheaper the better." You should not try to cast the wire along with the base because it would not be very strong and would complicate the mold for no reason; instead drill a hole in the resin castings and glue your wires into them.

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Post by nkuzmik » Thu Sep 01, 2011 3:46 pm

So I can't just pour resin or sculpy into my mold and go from there? What step is the rubber?
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Post by Joseph Osborn » Thu Sep 01, 2011 4:32 pm

nkuzmik wrote:So I can't just pour resin or sculpy into my mold and go from there? What step is the rubber?
The rubber is what the mold is made from. Unless you are using some other medium for your mold, which is outside of the scope of this thread. From your previous post, are you meaning to use a chunk of aluminum to make your mold? Like a rigid, injection-type mold that is used to make plastic parts? Sorry to ask so many questions, but the language that you are using does not really fit with the common RTV mold-making process.

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Post by nkuzmik » Thu Sep 01, 2011 6:14 pm

My original plan was to machine the mold out of aluminum, then use that to make parts out of sculpy. I'm getting the feeling that this isn't the best approach.
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Post by Joseph Osborn » Thu Sep 01, 2011 6:57 pm

nkuzmik wrote:My original plan was to machine the mold out of aluminum, then use that to make parts out of sculpy. I'm getting the feeling that this isn't the best approach.
Well, cost-wise I'd say no, it's not the best approach. You could machine your master from aluminum and make a silicone rubber mold, then cast a couple of dozen copies in urethane resin for not a lot of coin. Of course, a properly made aluminum mold would last indefinitely and with the right mold release you can cast urethane resin just as easily as with a rubber mold. It had better be a really simple shape and a really, really polished mold surface though.

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Post by Ziz » Thu Sep 01, 2011 7:13 pm

Rubber molds allow you to do undercuts and complex surfaces because the rubber can flex away from the finished part when you take the part out of the mold. A metal mold (steel, aluminum, whatever) can only do shapes that are essentially convex without any undercuts. Injection kits are done with steel molds because they need to make thousands of kits, but it also costs them 10's if not 100's of thousands of dollars for the mold. You only get 30 to 40 kits out of a rubber mold but depending on the size, it will only cost you literally pocket change by comparison. A gallon of rubber for around $100 shipped nets me upwards of a dozen molds.
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Post by nkuzmik » Tue Sep 06, 2011 9:27 am

The genesis of my plan for the aluminum mold came from the "We've got barn. We've got a stage. Lets have a show!" school of decision making. I had also originally planned to make the finished parts out of sculpy, so a heat resistant mold was important.

The product I'm looking to get out of this is a conical stand, 2.75" at the base, .5" tall, tapering to a .275" diameter flat at the top. I planned to mold a wire into the center which I would then twist however I need to hold the missile, bomb or other bit.

However, if I'm to be messing with something like a urethane, I'm guessing I'd be best off molding the base as solid, then drilling insert my wire...

Can anybody recommend a site that has a good How-To?
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Post by PetarB » Tue Oct 04, 2011 7:45 pm

Hi folks

RE: Degassing RTV

I've got a vacuum pump, and for the chamber I'm going to use my pressure pot which should work fine from what I understand. As I don't have an acrylic lid (like so many vac chambers do) I won't be able to see if the rubber has finished bubbling. So my query, is once the vacuum is up, how long should I wait before I release the vacuum? Any rough ideas?

Thanks.

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Post by tmajor » Sat Jan 14, 2012 3:15 pm

I was talking to the Salesperson at Sculpture Supply Canada and they recommended using the Moldstar line of Silicone Rubbers as they've got almost as much tear strength as Moldmax but dont require degassing and are mixed by volume and not weight.

Thought I'd mention that as I haven't seen Moldstar mentioned here.

I'm new to mold-making and casting so I just picked up the Starter Kit to get me started, but the Moldstar sounds like a good option in future as I don't want to get into having to buy expensive specialized equipment.

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Post by starmanmm » Wed Jan 25, 2012 7:59 pm

So.... how did it work out for you?
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Post by homyakchik » Fri Mar 02, 2012 9:30 pm

Dang. First mold-and-cast experiment, and it's already gone south. On a FRIDAY NIGHT, too. Dang.

I have the Alumilite Great Honkin' Big Beginner Kit, which I thought would be enough for a small mold. Literally, all I had was eight very small rocket nozzles (various sizes, 1/72 I think) from an old Wave Option System sprue. Got one of the Navigator's old sandwich containers (perfect mold shape, and just about the same size as the pieces spread out on the klay). Heated the klay (nifty hint, that). Figured I'd need about 10 oz of the rubber for this bottom coverage, and the rest of it for the top.

Nuh-uh. I had to mix another two ounces in and pour them over and stir them in (and pray). At that point I ran out of the catalyzer, although I think I've got enough silicone left for the top layer of the future squish mold. Thanks a LOT, Alumilite.

I really can't afford Alumilite prices for the stuff (the Smooth-On stuff certainly seems a better bargain), but the only dealer for the SO is down in Norfolk, and I'm betting they're not open on Saturday. Dangnation and blastoderms, anyway. Another week to wait for a UPS delivery.

Still, I was most careful in placing, bracing, keying and klaying the things that I set there--and I will need more than one set of reproductions, so it may wind up being worth it (eventually). But that seems like a gyp to not supply the proper amount of both substances a beginner would need to complete the job.

Alumilite. Peh.

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