Two part mold cunudrums part 2

[raser13]

hey guys and gals. If you saw my other thread then you'll know this is my first attempt at a two part mold. I now have the clay issue all sorted out. On to the new problem.

I had made a few molds with the much stiffer alumilite 2 rubber. And it was just to stuff to get parts with undercuts out with out destroying the mold. So I've gotten the 10 lbs of alumilite 3 rubber to make the molds out of.

It's working awesome on my smaller parts. But I just did the sauce section. I put the pour hole on the back of the saucer. Where it will be hidden under my impulse engines.

But now the mold is so flexible that if I stand it up on edge,the way I would have to have it to pour resin, it bulges outward. Which would distort the saucer section. If I lay it down, it leaves in a bit. Also distort the saucer.

https://i.imgur.com/rWzpVMG.jpg

https://i.imgur.com/J3WtO17.jpg

https://i.imgur.com/J2JYuIB.jpg

Is there a way to shore up the mold so the distortions won't happen? Or am I stuck buying the alumilite 2, and wasting this mold? I would rather not have to do this. I just wiped out my modeling budget for the next few months getting the large tub of the alumilite 3. Is there a better way to make the mold so that this will not be an issue in the future?

Any help would be greatly appreciated. I still have my engineering section to go. I can see this having the same issues when I make that mold

[Andrew Gorman]

Surround each half of the mold with a box or frame and fill it with plaster? Make sure to add some registration pins on the frame if you don't have them on the mold itself. If the mold is really whippy you might want to do this with the master inside to keep it from deforming. Just a suggestion...

[raser13]

thanks for the response. i'll give it a try.

[gsb5w]

I would think that's happening because the mold is too thin. The image looks like one mold is thicker than the other. Do they both bulge or just the thiiner one. If that's the case then you should be able to thicken the one side.

You could make a mother mold. My brother had some luck with a product from https://www.aeromarineproducts.com/

I don't remember which product it was but give them a call and tell them you want to reinforce your rubber mold and the will tell you which product you need.

[MEATLOAFr]

Surround each half of the mold with a box or frame and fill it with plaster? Make sure to add some registration pins on the frame if you don't have them on the mold itself. If the mold is really whippy you might want to do this with the master inside to keep it from deforming. Just a suggestion...

I agree, if you can, a stronger layer of a stiffer rubber on the outside

[gsb5w]

I would think that's happening because the mold is too thin. The image looks like one mold is thicker than the other. Do they both bulge or just the thinner one. If that's the case then you should be able to thicken the one side.

You could make a mother mold. My brother had some luck with a product from https://www.aeromarineproducts.com/

I don't remember which product it was but give them a call and tell them you want to reinforce your rubber mold and they will tell you which product you need.

[gsb5w]

Delete this post

[raser13]

@gsb5w the molds are fairly thick. It's an excelsior saucer. So it curves away from the high points pretty fast. The one side is a little closer. It has some alignment pins and a bigger planetary sensor that stood up more than the rest of the flat bottom. So I had to add that one thicker block to it to cover those sections of it.

@ meatloaf can you add stiffer rubber to the outside after it cures all the way? Will something like alumilite 2 stick to the softer mold having two different chemicals make ups? And do I need to rough up the mold to help with adheision? What would I use to do that? I wouldn't think anything like sand paper would work for that.

[EVApodman]

The weight of the resin in large molds can cause the mold to bulge slightly causing a distorted casting. This is why the rule of thumb is to have thick rubber walls around large castings. Unfortunately rubber is expensive and this can drive up costs considerably. Another solution is to have the mold in a support of some kind to prevent bulging.

When I cast small pieces I held the rubber together with rubber bands but this distorted the mold slightly due to unequal pressures on it which I fixed by using pieces of styrene to distribute the force evenly across the surfaces.

[raser13]

Silly question, but would adding something like adding popsicle sticks or bamboo skewers to the thinner parts of the mold to add structure work? Or would I'd make the mold have problems?

[gsb5w]

Check out this link. It goes over making a mother mold for your rubber molds.
https://www.youtube.com/watch?v=Fxk7zNn1hec