Suspicious of anything that could cause inaccuracies I have a measuring
and mixing procedure
that many may consider overkill - so do with it what you like.
For each cup I fill out an entry in each of the following 17 columns
(assumes 4:1 ratio):
1. purpose of batch (rudderL, uni2)
2. date (20-11-02)
3. time (20:16)
4. temperature (23.8)
5. relative humidity (41)
6. zero reading (0.0)
7. 100g reading (100.0)
8. check zero (0.0)
9. cup reading (say 12.2)
10. tare reading (0.0)
11. resin1 reading (say 45.7)
12. hardener reading (say 57.7)
13. calculated resin2 reading (60.0)
14. actual resin2 reading (say 60.1)
15. calculated zero reading (-72.3)
16. actual zero reading(-72.3)
17. result (ok)
Notes:
Point 7: I use Satrue scales 200g, 0.1g resolution, comes with a 100g
calibration weight.
Point 11 to 12: I use an "add hardener to read at least" table: 45.6
gives 57.0, 46.0 gives
57.5. etc.
Point 12 to 13: I use a household calculator ("add resin to read
exactly"): (57.7-45.7)*5Point 14 to 15: household calculator ("minus final
expected
zero
reading"): 60.1+12.2Designed to achieve:
Resin first, for wetting cup walls.
Resin last to decrease pouring accuracy needed:
Hardener (point 12) within 0..+0.5g is ok.
Final resin (point 14) within -0.2..+0.2 is ok.
All the scales stability checking I could think of.
For point 16 I expect +-0.1g or better.
The measurement procedure takes about 1 minute.
Finally, I reuse my mixing stick. I wipe it at the end of a layup
session and save it for the
next time. This avoids the possible influence of absorption (in an
unwanted ratio) using new
sticks.
Jan de Jong
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