Hi, fellow innovators1

Twenty-five years ago, working on a Dragonfly, including a session in Eloy
with Rex Taylor, I went with the crowd and got a ratio pump from Spruce.
Ratio pumps are fast and accurate and suitable for very small batches. They
also are in constant danger of being tipped over, potentially producing an
unthinkable mess if the lids come off the storage chambers. They also need
serious cleaning. Storage life is poor because the storage chambers allow
free air contact with the unmixed components. Also, filling the storage
chambers is a hassle.

About twenty years ago, I switched to a ratio scale as described in my books
and elsewhere. There is never any epoxy in the mechanism, so cleaning is
never a factor. Speed is about the same as a ratio pump, maybe even faster
for a large batch. It takes only seconds to place the two weights. Different
epoxy formulations can be used simply by choosing different weights. The
device is small enough to store on a shelf. A downside it that it is a
little harder to judge exactly how much a mixed batch will produce, so there
is a bit more waste. Also, epoxy components must be poured accurately from
some intermediate holder (like a laundry bottle) into the mixing cup. If the
builder over-pours, the batch is ruined. Price is zero. A good ratio scale
can be built and calibrated in a day. I'm still using my original, having
hauled it around for EAA demos.

Two years ago, I switched back to the simple calibrated pumps that go
directly into the shipping bottles, basically what West Systems does. Very
fast and simple. A downside is that there is a minimum batch size, so little
jobs are wasteful. Also, the hardener pump tends to crud up from contact
with the air if not used. Covering the nozzle of the hardener pump with a
little patch of aluminum foil will slow down this effect. Cleaning is
difficult, so the simplest thing is to just toss the cheap hardener pump and
use a fresh one. There is a minimum of component handling. I'm about to
start a larger scale production, so we'll see how that goes. Maybe I'll go
back to the scale.

I welcome comments.     Zeke Smith   Aeronaut Press