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Author Topic: Making Your Own Molds  (Read 564 times)

Bob La Londe

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Making Your Own Molds
« on: January 19, 2018, 10:40:41 AM »
An aluminum mold is usually machined using a CNC mill or CNC router.  In some cases a mold may be die cast in a steel mold.  The mold to make the mold (die) is usually machined and is much more expensive to make than a machined aluminum mold.  On the other hand it can produce large numbers of molds cheaply.  This is the way Hilts/Dolphin Sports (and I think Do-It) molds are made.  A metal mold might also be made by electro discharge machining where metal is erroded by electrical arcs.  This is typically done with a machined graphite electrode.  Also not cheap.  Of these methods CNC Milling a mold directly is the most productive way to make a single plastisol or lead casting mold.  It also works with lower life cycles than steel for hard plastic injection, and other types of materials.

If you have a machine capable of milling aluminum and making your mold you can buy aluminum flat bar at most local metal yards.  6061-T6 and 6061-T6511 come in various size extruded bar stock, and is the most economically priced.  7075 also makes decent molds, but its more expensive and its not weldable by common methods.  (When I was first learning I often welded in bad cuts on bar stock and remachined it.  Now its not worth my time.)

However you are probably looking for a method to make molds yourself and buy products you can use in those molds.  Bondo will work for a very limited life cycle.  Silicone will also work for a little longer life cycle.  Both will burn out from lead casting over time.  A modestly short measurable time.  Most spincasters use heat vulcanized silicone rubber to make lead casting molds.  It shrinks in curing, so they have to start out with an oversized master.  There are some "food grade" two part silicone rubbers that are catalyst cured.  They are generally considered good to about 390F.  That's much lower than the molten pourable temperature of lead.  Its more than adequate for plastisol.  Bondo is not really suitable for plastisol, but it might work if coated with something.  Getting back to silicone.  You can still make a limited number of lead castings in a mold made from silicone, but it will burn out.

Smooth-On has some catalyst cured silicones (mixed  by volume) that have very little shrinkage in curing.  This would reduce or eliminate the need to make your masters oversized.  Remember it has a limited life, and there is a learning curve to making your own molds.  There is no magic product that will instantly produce good results, except buying a mold from somebody who already has the bugs worked out if they have one you like. 
« Last Edit: January 19, 2018, 10:46:02 AM by Bob La Londe »