Rather than grinding a piece down to the desired shape, has anyone tried this: make a silicon rubber mold of the original piece, then fill part of the mold with more silicon rubber. Filling-in part of the mold is the same as grinding down the original piece.

Maybe it would be more expensive, since materials are involved, but would there be any advantages? Eg faster and easier and more accurate? Maybe it wouldn't be any of these things, but seems like it might be.

Also, you'd end up casting pieces that were still hollowed out, and thus using less plastic, rather than filling a hollow piece before grinding.

Just a thought.

Yet another possibility, but there could be a couple of problems.

If you used gravity to fill the piece (ie just poured it in) all the bubbles would rise to the surface that would be the finished face. You might be able to "paint" another coat of silicone to cover them. I've had limited success doing this to recondition old moulds.

Silicone doesn't always set completely level. If I look at the top of some of my moulds they are a bit lumpy.

Sometimes when you are grinding pieces it has to be done in the puzzle so you know where to grind or you might need to grind several pieces at the same time.

It takes 18-24 hours for most silicones to cure, so after you had spent 48 hours making a two part mould, you would have to wait another 24 hours for the filler to set.

Once a mould had been made, it would be much faster than grinding. You can turn pieces out every 30 mins. It might be better to grind one puzzle then use the best pieces as prototypes to make moulds. You can get an almost mirror finish that way. If you want hollow pieces, you can fill just enough before you grind and leave the back hollow.

There is an advantage. This could have saved me a lot of time. I am making a rhombicuboctahedron. I didn't want to damage the original. The centres have a hole because the original puzzle uses tiles. I didn't want a hole, so I had to cast the centre, make a piece and grind it down to accept a hand made cap, then cast again. I could have just filled the first mould a little and trimmed the part that makes the hole, here finish isn't so important because it will be covered with the cap.

Max