Alt-BEAM Archive
Message #03889
To: beam@sgiblab.sgi.com
From: Bob Shannon bshannon@tiac.net
Date: Fri, 28 May 1999 16:10:22 -0400
Subject: [alt-beam] Re: Working with epoxy, -WAS- a new idea for freeforming
James Anderson wrote:
> How do you go about coating the circuit? Currently, I'm using the two part
> epoxy stuff that you mix together before using (is this what you're talking
> about?), and think there must be a better way than just trying to paint it
> everywhere before it dries.
>
> Suggestions?
Are you having some specific problem coating your devices with epoxy?
Doing good work with epoxy is partly art. I find that with the common five
minute clear epoxy mixes, the ratio of resin to hardner is quite critical. Too
little hardner, and its too slow to dry and struturally weak. Too much and it
often dries with a yellowish tint. The epoxy itself may be strong enough, but
in this condition if often fails to bond to surfaces well enough.
In my experiance with epoxy (I love the stuff!) I've also found that the
texture
of the mix changes as its mixed. As the mix is first stirred, it will begin to
gel
slightly, almost like cooking scrambled eggs when the eggs first start to firm
up.
When this happens, slow down your stirring, and be careful not to stirr lots of
air into the mix. This is most often seen as white or silvery-looking threads
and many small bubbles in the still-liquid mix. If you see this, slow down and
let the air rise out of the mix. Try 'folding' the epoxy rather than whipping
it into
an air-laden foam.
Epoxy often likes to be mixed in smaller batches rather than mixing all that
you need
at once, and then trying to work with it as it hardens. Never allow any parts
joined
by epoxy to move during the drying process or you give up the majority of its
strenght.
If you need to fill an area, as when 'potting' free-formed electronics, but
some
modeling filler and add that into the mix. This will greatly aid the filling
process
and lighten the resulting device.
Lastly don't 'paint' the epoxy on, use a thin stick of peice of heavy wire to
scrape
a glob of epoxy up the moment its mixed (and still very fluid) and allow it to
run
down into the spaces between your components. Never try to fill more than a
few
millimeters at a time, because thick applications of epoxy are not as good as
several
thin layers, so long as you allow them all to dry completely before proceeding.
A good epoxy job might mean that you do a few millimeters of the project per
day, so
a simple Symet that might be done in an hour or two takes a week, but it will
be nearly
industructable when finished. For this reason I often build several identical
or similar
'bots at once to make efficient use of time. Small batches of robots get
finished together
rather than starting and finishing each one sequentially.
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