>I had the usual pump that comes from Michaels Engineering/Rook Metering and
>had horrendous problems
Not everyone has had these sort of problems with resin pumps. I
wouldn't be without mine, which is the same Michael Engineering
model, and has already built at least one Europa before I started
using it.
It's far from perfect - I can think of several improvements I would
make if I was going to make & market such a device. Switch from mild
steel pistons to stainless, for instance. And modify the geometry to
allow re-calibration without so much trial & error. I already changed
the moveable cylinder clamping arrangement which improved things
considerably. And I turned up a couple of little fruitwood caps for
the outlet pipes so they wouldn't clag up from exposure to the air
when left idle for too long. Another downside of the pump is that if
you want to switch from regular to slow (or fast) hardener, you need
to recalibrate as they are different densities.
The accuracy of pumps versus digital scales has been mentioned. You
should consider the absolute accuracy (dependent on linearity and
other things) as well as the resoluton of any digital scale. Work out
the possible error in measuring the mass of hardener and see if it
will achieve the required accuracy of ratio for small batches to give
the specified strength when cured. This has been discussed previously
on the list, so you should be able to find references to it - but I
can dig out the sums I did for my Ohaus digital scale if anyone wants
to see them.
regards
Rowland
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| Wilma & Rowland Carson <http://home.clara.net/rowil/>
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