[bassman843]

has anyone tried making their own molds like lc with lc's silicone that they sell?

[tubinator]

I have made and cut thousands of molds using many different kinds of rubber, most silicone rubbers that have room temperature curing temperatures are a 10:1 mixing ratio (10 parts rubber, 1 part curing agent). Vulcanized silicone rubbers usually have a vulcanizing (cooking) temp. at 350 degrees F.
What is your question about LC's? I did a quick look at their site and didn't see it so if you have specific ?'s about their rubber then post a link and I will take a look at it, and answer your questions.

[Smallie]

Smoothon makes a 1:1 silicone called Oomoo 25. It mixes with equal parts so you don't have to weigh materials. It picks up detail very well and it cures quickly. Price is among the best too.

Check out their website. Search this forum too - there are some threads that discuss silicone (RTV) molds in detail.

[bassman843]

LC list it as silicone kit

http://www.lurecraft.com/catalog.cfm...licone-kit:631

how do you guys make your molds I seen how lc does theirs and was just wondering what would be the best way I have a couple of Ideas

[tubinator]

Ok, first you want to make sure that the curing agent has a dye in it. This will help with getting a good mix of the material which is very critical, and it will make it easier to cut the mold.This time of year, I like to put the rubber near a heat source to keep it warmed up prior to mixing. It is much easier to stir/mix if the rubber is around 100 degrees, and getting the air bubbles out is easier too, at that temp.
2. Determine the amount of rubber needed. ie. 3/4" thick X 2" wide X 3 1/2" tall equals 1/4# mold rubber, or 113.5 g rubber and 11.35g curing agent
3. mix
4. vacuum
5. pour into mold frame (down the side of the frame, not on the piece)
6. vacuum mold
7. set mold aside to cure (if room temp is below 72 degrees, then I set the mold under a desk lamp, this will help with curing time)
8. cut the mold
Mold frames can be purchased from a jewelry supply, or you can make your own using steel strapping, just bend it into a U shape with a torch and vise. The sides can be made out of 1/4" plexiglass. To insure a good seal between the steel and plexiglass you can run a bead of wax around the edges. If you don't have a vacuum pump and bell jar, then I would suggest warming the rubber even more say to 125 degrees to help eliminate the air bubbles, and pour the rubber very slowly.
Any more questions, just ask.

[Vodkaman]

Thanks Tubinator, useful info.

I guess the vacuum thing is fairly essential to avoid bubble flaws. How is everyone else dealing with the bubbles? This stuff is too expensive to waste 3 or 4 tries to get a good result.

[tubinator]

One thing I haven't tried (because I have a very good vacuum pump) but have seen at Foundrys that make bronze sculptures is to paint on some rubber with a paint brush, replace the plexiglass sides, then pour the mold. Another option is to send it off to a professional, I normally charge $25-30 per 1/4#, but I only make molds for my jewelry customers. You might try to get in good with your local jeweler, they normally have a vacuum casting/investing system, and for a small fee they may let you use it.

[dramone]

i use this method:
http://www.youtube.com/watch?v=NVvGc7VDFvc starts at 4.09 min. (Bombs away Method)

it's working fine for me...

[tubinator]

Excellent demo's, remember not to breathe when it's bombs away!!!

[Smallie]

The Oomoo line of silicones, as well as others in Smoothon's catalog, do not require vacuum to eliminate bubbles. I mix with a mini spatula from Walmart and pour it in from one side of the mold box. I try not to let the stream from the mixing container land on the pattern. I think that is key to preventing bubbles.