"Acetal is a thermoplastic amorphous polymer. It melts around 350F but

melted amorphous polymers do not flow well enough to be cast. You will
not
be able to get it into one homogeneous mass. Acetal castings are made
from
resin. "


Acetyl is not an amorphous polymer, it is crystalline. It will turn
thin once melted

I think that will release from the mold fine because it will pull away
from the walls by about .020" per inch.

I think you may not like the end product. Most thermoplastics are not
just "cast" but are formed under some pressure. Roto molded parts,
"roto cast" the plastic isn't actually melted all the way but is more
of a sintered powder.

Your part will cool and solidify on the outside first, which will want
to arrest further shrinkage. So the inside will tend to create voids
and porosity. The outside skin ends up under compression and the inside
is under tension. When you go to cut it, it will "draw" towards the
cut. The thicker, the worse this problem.

Some plastics that are cast, such as some PVC, some nylon, some
acrylic, are actually polymerized in the mold, so do not rely on
cooling to solidify, there is less shrinkage so they avoid this
problem.

Delrin (POM) is not very castable, but you should try it and tell us
how it works for you.

Unlike nylon acrylic, abs etc, delrin does not absorb moisture and will
not need to be dried in your case. Heating it to melt it will dry the
surface moisture away