The silicone pot holders -- the only draw back would be that you
wouldn't have the different durometers as you do with the
That is neither the only, nor the major drawback. Urethane is
somewhat unusual for such materials in that although it’s seemingly
soft and elastic, it is not compressable. In other words, you put
pressure on it, and it’s volume does not change. Just like water or
hydraulic fluid, etc. Silicone is more spongy. If, for example, you
had a cylendar shaped plug of both silicone and urethane, each an
exact fit to a similar container except for being just a little too
high, and you wanted to cram it in anyway, and get the lid on…
With sponge or foam rubber, of course, you could do it easily. With
silicone rubber it would be harder, but you could do it. The stuff
would compress enough to fit in the container. The urethane, by
contrast, will not.
What this means for a press is that with contained vessels holding
rubber and a die, and a well fitted pusher (just as one common setup)
pressure on the pusher will give the urethane no other option but to
flow up into the volume of the die, pushing the metal with it, and
transferring the full pressure of the press up into that volume.
While the silicone will also seem to do this, it won’t do it to the
same degree, since as the pressure increases, some of that force
will simply compress the silicone further instead of causing it to
flow up into the die. In short, you loose much of the advantage of
the enclosed die, and the pressure exerted on the metal by the
silicone rubber will not be at all what you’d get with urethane, so
you get less detail.
Use the cheap rubber if you like. For some uses, where you don’t
have a contained space, for example, it may work almost as well. But
there’s a real reason why the higher cost urethane die rubbers are
used. They work better, and differently, and maximize the potential
of the press.
If you cannot afford the urethane, but still need good detail, you
may wish to explore making actual two part dies, that is both male
and female die parts or rigid material. This is, of course, how most
die forming is done in industry, where a steel die set consists of
both halves forming the shape from both sides, rather than just one,
relying on urethane to form itself to the other half. While formal
die making from steel may be beyond the skills of many who are not
trained in it, making a two part die from, say, liquid steel (epoxy
filled with steel powder) or similar products, is not that hard, and
for small production runs, they work reasonably well.