Reproduced with permission of the publisher of Lapidary Journal, January and February, 2007, Volume 60, Nos. 10 and 11.
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• Metal models ready for molding |
Powder separation moldmaking techniques can be used by moldmakers of all experience levels. For some, powder separation means entry-level with no scalpels (except for cutting air releases), consequently less danger of injury. For others, it means convenience, speed, and tight registration. I will be covering just two types of powder separation molds in this article. The first mold will be made with pre-vulcanized keys (instead of commercial metal “locks”) and powder separation. The second mold will combine pre-vulcanized keys with powder separation and hand cutting. Modelmaking will not be covered in this article.![]() Prepare your frame by dulling the edges of the opening with a sanding stick, because some of them come with very sharp milled edges that can seriously hurt you. You don’t want bevels, just smooth, non-cutting edges. You do, however, want to cut a bevel on one exterior corner of each side of the frame. This gives you a spot in which to slip a dull butter knife to pry the plates from the frame. Mark the frame with a diamond ball bur or a Dremel® electric engraver. Write “silicone” and “top/front” on one of the faces. This is important because the molds should be dedicated to only silicone rubber or only organic rubber, and it’s helpful to know which side the front of your model faces. ![]() |
Silicone rubber and organic rubber are seriously incompatible. If there is even a trace of organic rubber, any silicone rubber making contact will not vulcanize, resulting in a slimy, sticky mess. This holds true for the reverse situation: Any trace of silicone rubber will result in uncured, slimy organic rubber. Therefore, you should mark all model bags and note cards with either “silicone used” or “organic used” and the date when the model was last used. If you make a mold at a later date, use the same rubber again, or thoroughly clean the model using solvents, light polishing, heating, and pickling, or all of the above before attempting to mold in a different type rubber. |
sure to follow the manufacturer’s specifications. Making the keys is like rolling out pastry dough. Start off with a piece, maybe 5" long. Peel off the safety paper and place the rubber on a piece of wax paper sprinkled with baby powder or jeweler’s talc. Flip the rubber to dust both sides and begin rolling the rubber thin with a rolling pin. (NOTE: I bought the rolling pin at a discount store, and I do not use it on food.) A large dowel will work, but a rolling pin is much easier to use. Stroke in different directions to get an even thinness, and rub on more powder if the rubber sticks. I visually aim for 1.2mm for my thick keys, 1mm for my standard keys, and 0.5mm for my tiny keys. |
Place sheets of rubber, alternated with pressure plates, into the frame until it is firmly filled up just beyond the top surface. Cover with another piece of foil and the second frame plate. This mold frame sandwich is placed into a 330°F |
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The containers must have tight lids to keep the keys dust-free. After all, the cut, powder-free surfaces are what bond to unvulcanized rubber! I usually don’t cut too many keys at one time, since a dropped container |
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