I need to cast some half spheres using tinted resin. A local plastics company sells molds but they only have about 3" diameter and I need them to be 1 3/4" to 2" diameter. Does anyone here in Lettervile know of somethig I can use for a mold thats about this size and shape and the resin won't attack? It doesn't have to be a perfect half sphere, just something close. I would prefer to buy these already made but I don't think I'm going to get that lucky. I'm doing some non-sign related art projects and I keep picturing this shape tinted amber and some in dark green. I feel like that guy in, I think it was "Close encounters of the third kind" who was building the tower in his living room and didn't know why but he had to do it. A lot my projects get stated that way. I'll have to have my helper do this because if I smell that stuff I'll have a real bad day. I used to use it to patch surfboards so I know it eats styrofoam cups but not other types of plastic. Thanks
Posted by Laura Butler (Member # 1830) on :
Chuck, I remember seeing an article in an old magazine-I think, SignCraft about someone doing molds. I don't remember what issue. I'll try to find it.
Posted by Kelly Thorson (Member # 2958) on :
How about egg shells Chuck - Sold cheap by the dozen. Posted by Rodney gold (Member # 4065) on :
Make the mould yourself , it shouldnt take more than 20 minutes. Buy ANYTHING thats the diameter you need , embed 1/2 of it in plasticine (modling clay) at the bottom of a paper cup and buy a 2 part RTV (Room temperature vulcanising) silicon - you can get it just about anywhere , normally from places that sell casting resin. Mix it up , pour it in , wait for it to cure and then brak the cup and remove the ball and plasticene and voila , you have a mould. The life of the mould depends on the mould material and the resins , some resins are agressive and some less so. The Resin supply guys should be able to supply you with EVERYTHING you need to do this - it's not rocket science Posted by jimmy chatham (Member # 525) on :
cut a pingpong ball in half
Posted by Jillbeans (Member # 1912) on :
Hi Chuck... Francis Lestingi from NY is an expert on mold making, in my opinion...maybe he would have an answer. Love- JILL
Posted by Joe Rees (Member # 211) on :
It's not rocket science, but it can be damm frustrating. There are some combinations that don't work. For instance, West Systems epoxy does not like silicone. We have used silicone release agents that prevented the West from kicking, making a gooey mess. (Letting the release agent dry thoroughly before pouring in the epoxy helped, but it still seemed to grunge up the mold). We have used release agents that were not 100% silicone - BIG NO-NO. Silicone lubricants will NOT work as a mold release.
The only acceptable results were using silicone for the mold itself, then no release agent is needed, and nothing so far has harmed our molds. Two part RVT is expensive though. Our source is SmoothOn http://www.smooth-on.com, but they're a little hard to deal with. They only sell through distributors, not direct from their web site. The problem with that is the distrubutors are only order takers. You have to know exactly what you want when you call. If you make a wrong choice the distributor cannot advise you or warn you. Believe me, the information I learned about molds was painful.
Still, I wonder if a 'caulking' variety silicone could be spread over an object to make an useable short-term mold. I'd never risk it over something I had put a lot of time into, but it might be worth experimenting on a simple shape like a sphere. Anyone done it? I'm sure you'd probably need a release agent cuz that kind of silicone is more of an adhesive till it's cured.
Posted by Rick Chavez (Member # 2146) on :
When I used to do this. I would make a wood plug (usually on a lathe) then cast a negative, depending on the complexity in halves or the whole thing then cut it, then you have your mold! Depending on the casting material, you get the appropriate release, I think silicone spray worked well, but doing a transparent casting is a lttle trickier
Posted by Mike Pipes (Member # 1573) on :
Joe, I buy from smooth-on all the time, straight from their website! Ya must not have been there for a while, I've been buying casting resins and mold rubbers direct for about a year now.
Chuck, ya know those little candy and toy vending machines you see at stores? the ones where they have the toys in the clear containers? those containers might work for ya.
For about $50, you can get a silicone mold kit (enough to make a few small molds) and a kit (about one quart) of low-odor casting resin (urethane) and some tints from smooth-on.
Posted by Chuck Peterson (Member # 70) on :
Some good ideas. Thanks everyone.
Posted by Joe Rees (Member # 211) on :
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