Casting Questions

[THarvey]

I am thinking about doing some small casting. I plan to make my first molds from silicone caulk, using the tutural in our library.

I have a couple questions:

1. Is there a formula to calculate the amount of resin needed to fill a mold? I know how to calculate the volume of the mold. I am unsure how to translate that to the liquid volume of resin.

2. Do I need to use some type of mold release with the silicone molds? If so, what works best?

3. I will most likely cast these in my garage, without a pressure pot. Any words of caution, I need to hear?

Thank you.

Tim

 

[RHunter]

Tim,

1. I just fill the mold with water, pour that into a cup, and mark the line- volume needed to fill mold found.

Transfer that measurement several cups and mix directly into the marked cups.

Now if you add fillers or liquid colors (I have been known to use Testors Model paint) you may get more total volume then your mold will hold- but not much, and using disposable cups, you may get some left in the cup to cure. But that's a good thing, you can test for cured by checking the leftofer resin in the cup- saves you from poking at your blank in the mold.
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2. Mold release, I don't, but some folks use a dusting of baby powder.
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3. CAST OUTSIDE, WEAR A RESPIRATOR!!!!!

PR is VERY STINKY, Alumlite is no where as stinky- but still be safe, you only have 2 lungs.

Mix carefully so as not to mix air into the resin.

Once you add your catalyst, you could vibrate your mixing cup to "shake" out the air. I put my mix cup on the bench and run my jig saw next to it (without a blade) to make vibration. Some folks rest their mixing cup on their scroll saw. I just bought the HF Ultrasonic Cleaner w/ heat to help degass my mixing - I use some powdered pigments that really need to be mixed well to break up clumping.
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grub32 on youtube has the technique I am working on at present.

http://www.youtube.com/user/grub32

Good luck and welcome to the addiction, I spend more time casting then turning nowadays...

-Doug

 

[Jgrden]

Spongy

I have been trying to get a rock hard insert, inside a bullet but it comes out spongy and won't finish. I heat the bullet with a mini torch so that it is too hot to touch, pour the Allumite in and pressure it at 60 psi, then bake it in a toaster over at 150 degrees for thirty minutes. I am sure the mixture is 50/50. What is happening? I also continue to get air between the decal and the resin or Allumite. Help.