What material to use to mould vac forming mould for R/C Car bodyshells

[Guest]

I've got a couple of Ministock bodies I wanted to try to reproduce for peanuts using the vaccy former at work. So the shells could be used by the kids for a fun lunch time project! I thought it'd be worth trying to cast the shell in resin or some form of plaster and then use that as the former for the new shells.

I've tried in the past with plaster and got some ok results but former was very fragile and didn't have much longevity!

I can kick myself but when at uni, there a new casting material was demonstrated. The stuff was in a fine powder form, mixed with water and could either be used to slip cast hollow items or could be used to pour solid castings. The material could be coloured or thin forms could be reinforced with fibreglass matting for more strength and laid up in layers. The great thing about the stuff was that it really captured details superbly, even down to fingerprints and the final thing had a very similar quality look, somewhat akin to an ABS plastic injection moulding. It was very tough too even when in very thin section.

Any Ideas what the material was? It strikes me as if it would be widespread in the film, tv industry for pro making and prototyping etc.

[Guest]

Expanding foam filler?

just a thought..

[Guest]

vynamould, its a heat soluble material, heat it up pour and let it cool, once cooled it can be used as a master, once you are done with it you can remelt the material and use it again....... can be reused about half a dozen times before qualitiy of finish drops off and you need to bin it........

sad thing is dont know who stocks it now adays...... not used it for a long time

[Guest]

The prob with that is that the bodies have some details which would need small pin holes in the former to allow the vacuum to pull the plastic right into the corners.

I've got a couple of stockists for the vinamould, it does make a nasty pong when you melt it though! Also I don't know how I'd melt sufficient quantities without a proper melting pot either.

TOMPS sells the stuff and has a guide to using vinamould too.

[Guest]

Hi m8

Stick with plaster but go for a harder version not just good ole plaster of paris.

Also buy some thin plastic tube, (Most model shops sell styrene with about a 1/8th hole in.) buy some of this, and using superglue stick to the inner surface of the shell using lengths long enough to clear the upsidedown bottom of the shell. Place these at any low points, or bit with high detail in them. Then spray with some mould release, (most of the time plaster won’t stick to ABS, anyway) then fill with something like Crystacal R (www.cfsnet.co.uk/acatalog/CFS_Catalogue__Casting_Plaster_174.html) This is very hard plaster and has a very good surface detail when set. When fully set cut off the excess lengths of hollow tube, and turn out the mould. You should now have a body shell mould ready to go straight onto the vac table.

Hope that helps

J Don

Ps, vinamould will distort the shell as it gets very hot.

[Guest]

See Don's PS, Vinamold pours at about 145c, probably too hot for the original shell.

If it starts to overheat it will smell, back off the heat and add some more to the mix to cool it. Larger quantities can be melted in a jug (coffee pot) within a standard saucepan using sand to insulate.

J.

[Guest]

Thanks for all the advice guys!

I'll go with Don's plaster and plastic tube idea - Should work very well! I'll give that a bash and then post the results!

:dancing1:

[Guest]

I just need to find a local supplier so I don't have to spend crazy amounts having a big heavy bag of plaster sent through the post!

[Guest]

Hi Alan,

As an artist I've worked with resin. I also use resin for lost parts and scratchbuilts in scale modelling.

I use RTV Silicone (Room Temperature Vulcanizing). There's no temperature involved here. All you have to do is mix the appropriate amount of catalizer according to instructions.

To have fine details, first coat your original with a release agent so you can separate the mould from your original. Petroleum Jelly will be fine. Coat your original model with jelly then wipe it and buff it with a clean soft lintless cloth.

Place your original on a slab of modelling clay, a little larger than your original. Place a wall made of modelling clay around the slab to prevent silicone from pouring out.

Mix RTV silicone according to instructions, just enough to cover your original with a thin coat. Mix slowly to prevent buildup of bubbles.

Brush a thin layer of silicone to the original. This will prevent bubbles from forming then build up the layer.

When silicone is dry, mix another batch of silicon to make the mould thicker. You can add fiberglass to reinfoce the mould.

Next step after the silicone mould is dry, pour plaster of paris backing over silicon and you're done.

The RTV silicone is very flexible, you can use it on originals with undercuts.

[wonwinglo]

Try your local builders upply stores,they sell good quality plaster in big bags that will last you years.