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Yes. You need to have a fairly decent original to make a "mold" for casting the new piece. In my case, my heater control piece was broken in two; if you look very closely at the photo of the molded parts, you'll see the line where the original was broken (we tried to glue it together before we molded it, but you can see we did not glue and sand it perfectly, so the line showed up in the mold and thus new pieces).
If you go to the Smooth-On website, http://www.smoothon.com/
you'll see how we are doing this. We selected a silicone molding material to make the molds. Here is a photo of the heater control mold:
silicone mold
Then we selected a "resin" to make the plastic pieces. In this case, a white polyurethane to make the solid colored pieces, with some dye --a few drops of black dye produces the gray shade of this piece. We also selected another clear polyurethane to make the speedo piece and other clear parts.
We happen to have a vacuum pump (don't ask) for use in degassing things:
Vacuum pump
I am probably making this seem a lot easier than it really is...note that I'm a materials engineer by training so I do stuff like this at work all the time! Figuring out how to do this has been quite tricky (but fun). In fact, I intially just tried to make a mold with (cheap) Home Depot RTV 108 silicone. Besides not curing properly (the mold was a sticky gooing thing), the results were also disastrous since we didn't have a vacuum pump at the time, so it had air bubbles throughout it. Casting resin into this mold would have produced a part with lots of air bubble looking cavitities in it (so we didn't even try). The second attempt entailed buying "dental molding material." This is the stuff they use to cast molds of your teeth when then need to make you a crown. :)
Again, the latex mold looked pretty good (except for the air bubbles trapped in it). Problem is, latex shrinks up when it loses water (and in AZ the relative humidity is such that water is sucked out of things pretty quickly), and in a few days, your mold is all shrunken up and no longer dimensionally correct. So it is only good if you work quickly and only plan on casting one part. When the dentist does this with your teeth, they throw the mold right away, so it's not necessary to make it permanent.
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