question about making a mold with oomoo . . .

[Lflank]

I'm ready to make a mold for the smart disc model I've been working on (it'll be my first two-sided mold). I'll be using Smooth-On Oomoo to make the mold. The basic shape of the model is a flattish disc with a much smaller central area that projects about two inches above the rest. Here's my question: it would save me an awful lot of Oomoo if I can cover the flat disc part with just a half inch of mold, let that semi-dry, then place a paper dam around the smaller central part and pour Oomoo into that to mold it. So what I need to know is whether thosee two Oomoo layers will then bond to each other and form a single piece if I do that, or if I'll need to treat the smaller central part as a separate mold piece, and put registration holes etc in for it.

Any help would be greatly appreciated.

 

[fastburst]

I personally would think having them separate would be be the way to go as far as being able to add finishing details. I did the that before with what you were asking with the 2 layers and it didn't work out so well. You may have a better result than I did but in my opinion it came out better with separate molds and added greater detail(s) in past projects. Only hard part in doing that is finding a happy medium on fusing pieces together.

As for the disk that you are working on, I haven't tried using a mold to make them found it easier to use old Tupperware bottoms with some sliders and a good-ol soldering iron and burning in the details along with some Foamies which came together really quickly. However, if I would have taken the time to actually mold it, who knows it could have been just as great, I just wanted it functional for me.

There may be a way to fuse the mold(s) like you were asking I just didn't find a successful way when I did it.


It does pose an interesting question if it can be done and look forward to the replies.

-James

 

[Lflank]

As for the disk that you are working on, I haven't tried using a mold to make them found it easier to use old Tupperware bottoms with some sliders and a good-ol soldering iron and burning in the details along with some Foamies which came together really quickly. However, if I would have taken the time to actually mold it, who knows it could have been just as great, I just wanted it functional for me.

I'd probably use a Frisbee as a base and just add parts to it. But I'm doing this one as a cast piece just as a way to learn how to do two-part molds (and I made the model from clay just to learn how to do the sculpting--alas I don't think clay sculpting is for me). I've already done one-part molds that were flat on the bottom, and deep one-piece molds that I slit up the side to get the cast pieces out. So the next step up is a two-part mold.

There may be a way to fuse the mold(s) like you were asking I just didn't find a successful way when I did it.

It does pose an interesting question if it can be done and look forward to the replies.

Well, I'll give it a shot and see how it works. I'll post the results, for better or worse.

 

[Lflank]

An update--good news and bad news.

The good news is that the mold-making went well. I decided to make the model a little bit thinner and so ended up not having to try the smaller central piece. Got a nice crisp mold.

The bad news--when I tried to cast a piece using SmoothCast, I had lots of air bubbles in the top half of the cast piece. I did have a vent hole near the fill hole, but looking at the shape of the model I can see where the blade parts would be prone to air bubbles, since they're wide and flat, and have only one spot for air to escape. I can't even really tip it around a bit to let the air bubbles out as I'm pouring, because the SmoothCast hardens so rapidly and so suddenly.

I'm going to insert a few more vent holes at various places, and try it again. But I'm quite worried now that the whole basic shape of the smart shuriken--wide and thin and flat--is inherently prone to lots of air bubbles, and may not ever work very well as a cast piece.

Any advice would be greatly appreciated.

 

[Lflank]

In looking at Smooth-On's website, I see a resin called SmoothCast 322 that has a much longer pot life and lower viscosity than the SmoothCast 300 I'm using now. Maybe that will fill my mold better and give me some time to tip it around to let all the air bubbles work themselves out. Anyone have any experience with this stuff?