I have bought the Pelouze electronic scale, a neat little unit for postal
weighing, sold at office supply stores for about $60. I have a few
observations about its use and quirks which may be of interest to other
builders.
First, it has a best resolution of 2 grams, which means that a resin batch of
20 grams may well be off by 10% in the resin/hardener ratio. Hence, you will
not want to mix quantities less than about 40 grams, if 5% is your max.
acceptable error.
Next, after placing an empty cup on the scale and zeroing, I normally pour in
a predetermined amount of hardener, followed by the proper amount of resin.
A quirk of this scale is, that after zeroing, while the scale is reading
zero, small variations of weight will be considered anomalous and will be
automatically subtracted. This means that if you pour your hardener in at a
slow enough rate, the scale will continually zero itself out and even with a
quarter cup of liquid, the scale will still read zero! Not good!
Well, there is a fix for this behavior. Simply place the empty cup on the
scale and zero it, and then before pouring in the small amount of hardener
place a small weight, say a mixing stick, on the scale, begin pouring in the
hardener and remove the mixing stick after the reading is well positive. At
this time, everything will progress as it should and you will get your proper
ratio!
BTW, I mix small quantities of resin/hardener by volume (3:1 with Aeropoxys)
using two cheap plastic hypodermic syringes. These are calibrated in cc, and
they make very accurate ratios possible even in very small quantities. They
can be readily cleaned with alcohol and reused again and again.
Chuck Popenoe
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