Re: [CAD_CAM_EDM_DRO] Re: Hot rolled router frame: added note

In a message dated 3/5/2003 7:35:26 AM Central Standard Time,
leswatts@... writes:

> I think most epoxies and polyester/styrene resins are too viscous to flow
> out well, but I know some very low viscosity specialty resins can be had.
>

Les:

I have been using an epoxy resin called "Epon 815" mfd. by Shell Chemical,
also distributed by Miller-Stephenson in plastic gallon-jugs, on up to 55
gallon drums. It is as viscous as and LOOKS exactly like that clear Karo
syrup used for pastries, etc. It is cured with a catalyst with a name I can
NEVER remember; something like "Tetraethyltriamine" or whatever, ALWAYS just
abbreviated as "TETA". This is added to the resin in a ratio of 1:10. That
is, TEN parts resin plus ONE part TETA. It must be stirred very well, and
preferably vacuumed to float bubbles to the top, and then cured "overnight".
It gets unmanageable in a couple of hours, but not really "hard" for several
hours. It continues to harden for 24. This stuff is used extensively to
"pot" electronics, to make prototypes, or even mold production-parts, as one
can make a mold with just soft RTV-11, using a "real original" as the model,
and then "peel off" the RTV image, and pour the epoxy into that. It will
very faithfully "copy" scratches caused by fine steel-wool on the original!

It is SURELY viscous enough to make "lenses", but it WOULD require the
spinning motor be left running for 5 hours or more! BUT, it may not be
ideal for this, as any excess TETA that doesn't polymerize "floats" to the
top, and leaves dozens of little "bubble-pockets" per CM, when wiped off the
hardened surface. I have discovered that this frustration can be at least
partly reduced by using slightly LESS TETA, but I have NEVER been able to
learn if this WEAKENS the final cured material, or simply slows down the
cure, which it definitely DOES do!

Last gallon I bought (a year back?) cost me about $70 from M-S, as I recall,
but their price for the TETA (quart bottle is MORE than enough for the gallon
of resin) was considerably less than I remember from Shell direct (they have
a distributor here), though Shell charged me less for the resin! Guess the
total was about equal from either source. The M-S jug was nicer! LOL, but
true!

I have mixed variously liquid printers' black-out (used for touch-up
lithofilms), chalk-line refill powdered chalk, rice, and beach-sand as
pigment or fill, all with success. It seems it would perform as a fine
water-proof adhesive for wood, but I soon learned it is not at all "STRONG"
for that purpose, though it DOES kinda work. (Polyurethane wood glue is
much, much better for a strong waterproof bond, wood-to-wood!). The Epon 815
sticks to CLEAN (JUST-sanded and solvent-swiped) metal very well, but I don't
think I'd want to fly in an airplane "glued up" with the stuff.

It seems to shrink physically a TINY amount on curing, but I'm not sure that
is no more than my imagination. It does NOT expand on curing.



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