Re: [CAD_CAM_EDM_DRO] Epoxy

In a message dated 20-Dec-01 21:20:14 Central Standard Time,
wscalione@... writes:

> That seems a bit on the expensive side. How about using a regular
> epoxy and using common items for the additive. Laser toner for black?
> any ideas? How do I keep bubbles from forming?

Bill: I use Shell Epon 815, a "pourable" epoxy. Comes in gallon jugs, and
uses "TETA" (some organic chem. name like "tetra-ethyl-tri-acetate" or
whatever) as catalyst. Mix 10:1. Must use a balance-scale, and be within a
few percent. Too little TETA, and the result is soft. Too much, and it
"floats" to the top, and leaves droplets all over the top of the pour, which,
when "sponged off" after hard, leave semispherical dimples where the drops of
TETA were floating. This is a very hard, stable "plastic", nearly colorless.
Mixes readily with any powered pigment such as soot, copier toner,
chalk-powder, any dry powder paint-pigments, etc. Also, lithographer's
liquid black-out mixes fine, too. Softens result a bit, but doesn't take
much of it to make it reasonably opaque/black.

Bubbles? I built a plexiglass "bell-jar" (rectangular box with open-side
with pourable-RTV rim, to seal against flat surface (another slab of
plexiglass/Lexan) for placing such inside, and drawing vacuum on it. That
makes bubbles expand so they float readily to the top, and after quarter
hour, release the vacuum and let the pour cure in the atmosphere. Makes a
trememdous difference! I also tried using an electric stirring-rig inside
the vacuum, to mix the epoxy so it wouldn't "mix-in" air, and this "kinda
worked", but it was so much hassle that I didn't continue that method.

Lotsa luck!


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