Topic: Ask a Caster! Got a problem? Get help here!

[DocOutlands]

Just a thought I had, since I have a problem.   

[DocOutlands]

I have a mold of a head that consistently has an air bubble in the same spot every cast.  Does this indicate a need to redo the mold using a different angle on the head?  Would putting the mold into a food-sealer marinating box and then "sucking a vacuum" on it work?

[Clonehead]

Doc, if you want to save that mold you may be able to use one of two or three methods. One is the super squeeZe method where you squeeE the air out before you pour and release as material fills the void. You can just pour enough of the part to get material to the problem area, squeeze it a bit to force material into the problem area, let it set up some and then pour the rest.
Or the most effective solution for me is to cut a vertical slit in the mold from the outer edge of the problem area up to the top of the mold. This will allow you to spread the mold in that area as you pour and will give the air bubble an avenue of escape.
What part is it so I can better understand where the air is getting trapped?

[DocOutlands]

I think approach #1 solved my problem.  I was consistently getting an air-bubble at the top of one particular head in the same spot.  I've changed my squeeze tactics and I think I may have it licked.  I've gotten two in a row without the bubble.

Thanks!

[spudafett]

mold release agent...

is there a cheap home made alternative?

I read that petrolium jelly, ie- Vasoline, works well. 

I also read somewhere that you can mix vasoline with water untill it is a liquid and use it in a spray bottle... if so that would be my best bet I think...

I'm probably going to start on some molds tonight!  wish me luck

[DocOutlands]

I haven't yet moved into the world of release agents. 

[Clonehead]

I read along time ago that vasoline would work for this but don't know if it will work for the products we are using.
It would be an experiment.

[spudafett]

well i guess I'll try using vasoline on one of the two part molds I did and not use it on the other and see what happens...

[narceron]

While I don't have any experience with this resin casting, I've been green stuff molding for years, we used oil, vegetable, I think, to keep things from sticking to those molds and it was GS on GS, so it had to work,

wait, great googly moogly, I bet I can use the resin on my GS molds. . .Woot!

[spudafett]

lol of course you can use resin on that... heck I was using clay to help form my two part molds and the clay holds shape pretty well too so I think you could even use clay to make temporary molds....

I might try that...

[narceron]

I have so many skulls and gibble from my GW days, could be awesome,

[B.R. Steel]

I've got a question.  Does anyone ever have a problem with their dremel melting the plastic that they're trying to "dremel away"?  I have a fairly old dremel rated for 5,000 to 30,000 rpm.  Is even the slowest speed here too fast?

[Clonehead]

for me it is, b.r., although I have never tried using it to cut resin before. the friction caused even by that slow speed will create enough heat to make plastic or styrene melt. I suggest you try a good cordless drill to chuck your cutting, sanding, or grinding wheels and bits into and work with it. That way, you can regulate the speed lower, at a pace that works for the material that you are working on.

[spudafett]

It takes some getting used to, just work in short and quick bits.  Like tap the surface your sanding, then let it cool, tap it again for a second more, and then let it cool.  Don't just hack into it for a good minute or so and expect it to sand right...

I've done that in the past and it melted the plastic and wrapped around the sanding drum... and I've also had molten plastic thrown in my face...

Just try practicing on some scrap parts untill you get the feel for it.  Dremelling is realy an art more than it is a technique....  if that makes sense... you realy have to work at it untill you get the feel for it.

go slow, work in short bursts, and you should be good.

[B.R. Steel]

Thanks for the advice guys.  Although my cordless drill would be a bit awkward for most things it might be just what I need for some projects.  Looks like for other things, I just need to learn how to work the dremel better. 

Thanks again!