Hi,

I am used to work with epoxy and glass moulds, but now I am going to produce cylinder heads and intake tubes for a 1/4 scale dummy rotary (LeRhone). I have heard that using polyurethane resin in silicon moulds is a perfect method for this. Can anyone explain how to do this or know of any links describing it? Thanks in advance!

Cheers,

Magnus

PS Is it spelled mold in the US? The Spell Check attacked all the moulds.

Everything you want to know is right here:

http://www.polytek.com/

The model railroad guys have been doing this for about 20 years now. You cannot use straight urethane for casting as it flakes and shrinks after about two years. I have seen the older urethane kits and for most purposes they are junk now.

They also vacuum down the blue silicone to remove any possible trapping of air bubbles which then show up in the surface of your finished product.

There is some stuff with fine metal inside which is a bit more expensive, but takes the heat and stays pretty rigid. It will also cast to very thin sections and not break upon knocking around.

I would suggest that you investigate with those of model railroad interests.

Wm.

nomma, here are some molds I made using silicon and then alumalite casting resin. Both products came in a kit purchased at Toledo last year. The molding compound is pretty easy to use. You need to make a mold "box" and then add the silicon. What you may want to consider is molding half a cylinder at a time. You want the separation line on the center of the cylinder. I would place the cylinder half fin side up on a flat surface. I use a piece of glass, then pour the silicon. Here are a few parts I made for a manifold. I needed 8 of them so I made one from styrene and copied it via the molding process.
The last picture is of the pieces added to the manifold.

Hey, Bob.

Looks sorta, kinda, exactly like something that would go on an SE-5

Les

Les, lol you are da man! Exactly right too . I just about have them finished being primed, so next step is the burnt copper color. Man it's one detail after another [X(]!

Hi there from down under If you want to do it on the cheap you could use latex rubber from dental supplies . powder or liquid, and bondo, use only a small ammount of hardner in the bondo to give more working time, if the mould does'nt have to be flexible you can use bondo also for this.....I thin the bondo down to thick runny, with resin and use it as a gel coat on the mould first, then back it up with regular bondo. I use plasticene or as you yanks might call it modelling clay ( the stuff that is oil based) to give a half mold centre line. If you want the mold to last ,back the bondo up with plaster to stop it distorting with time....a coat of pva glue brushed onto the bondo before the plaster helps the plaster stick. dont forget the pva release agent first!

Here in San Diego, I tried to buy some "dental" plaster, and was shut down completely. The supply houses will only sell to Dentists[:'(]

Liquid latex is available here in the form of a stuff called "Moldmaker", and I have used it some. The model railroad supply stores also have a liquid latex for making small parts.

Les

Keep an eye open for the next (July) issue of Model Airplane News... Vance Mosher will have the entire "Scale Techniques"column dedicated to resin casting scale parts. Great Pix of the process are included.
GY

As for copper, Alumilite has a copper powdre that you brush the surface of the mold with prior to pouring in the resin.
Here are some pics of a set of landing gear that are almost entirely resin cast. The resin cast parts are added to the stock landing gear.
Molding is fun, but very expensive on a project that ends up comprising 30 to 40 individual molds. Beats scratching 8 parts individually though.

Hi All

All the materials you'll need to make almost any detail or custom parts, mold or cast, from tyres to control horns are available from Smooth-on .com.

The list of urethane plastics and rbbber are vast. Also RTV silicone.

Prices and quantities are better than some repackagers of similar products.

Steve

Thanks everyone!

The pictures of those landing gears are just too much! I hardly believe my eyes!

Cheers,

Magnus