Reply to Ian Seager,
I wouldn't feel happy about weighing small quantities on a mixing pump. The
problem is that inaccuracy can arise from non return valves not closing
cleanly, air bubbles in the wrong place, leaking valves etc. The errors are
acceptable with quantities of say 100 gms. but I wouldn't trust the accuracy for
any less.
I had an old mechanical (except for the scale lamp) chemical balance which will
easily resolve to one drop, less than .1 gm. The scale is analog too, even
easier to use. 20 quid from Anchor Surplus, Nottingham. There are digital
balances used for paint colour mixing of similar accuracy which are ideal, if
you can find one at the right price. :-)m&d
I always mix fast epoxy by weight too, I find it cures off so much better, you
don't get the slight stickiness that sometimes happens if you do it by eye, or
don't mix long enough. Don't forget mix ratio by weight is not quite the same as
by volume.
If you are mixing by weight, use a spread sheet print out 10 to 100 gms in .1 gm
steps, next column previous cell times 1.25 gives the weight including hardener.
If you don't understand spreadsheets, this is a very worth while way to get
familiar, then you will know how easy they are and be ready when you come to the
weight and balance. IMHO Anyone who does a weight and balance by hand is a self
made martyr. Why write it out every time when all you have to do is type it in
once, in exactly the same format and it's done for all situations.
Graham pontificking again, sorry!
|