Making a mold frame for RTV:
Aluminum bar stock, 2 glass plates, 2 spring clamps, and a sprue
You can find aluminum stock in almost any thickness and width - I
beleive we use 1/16th" to 1/8" in thickness - and a width to
accomodate the mold master. You'll need a vise and a hacksaw.
Figure out how much material you will need, cut it to length. Bend
it into a "I_I" or "U" shape that will contain the object you are
molding. Allow a little space so it won't touch the sides. Make
sure that the width of the stock you've chosen also allows a little
wiggle room. Clamp it straight and true in the vise before bending.
Clamp the 2 glass plates to the "U" with the spring clamps, and you
are ready to test pour. (The spring clamps we use resemble huge
clothespins and can be found in most hardware stores)
Test first with syrup or molasses to see if there will be leaks.
Usually the two corners expand a bit when bent sharply and need to
be sanded flush with the rest of the frame. Sometimes you haven't
made your bends square and true, and you may have to do some
tweaking and further sanding.
Glue a plastic, wax, brass or aluminum sprue former at the bottom
of your "U". Use a plastic, brass, or aluminum rod as the sprue to
your piece. Glue everthing in position. Some plastics will actually
bond to some RTVs, so check/test first on small samples of whatever
you have available.
Not clear enough? Let me know.
Brian P. Marshall
Stockton Jewelry Arts School
Stockton, CA USA