Well, the house is now insulated, so my thoughts drifted back to spine testers, and converting my arrow straightener to a spine tester.But I won't be experimenting in the near future - my plans for a combined arrow straightness/straightener/spine tester workstation have just been scuppered by the last electricity bill and a trip to Homebase for insulating and draught excluding material
Excellent use of pencils, annotation and smiley facesWell, the house is now insulated, so my thoughts drifted back to spine testers, and converting my arrow straightener to a spine tester.
So I identified a whole load of materials, parts, bracketry, bearings, etc and was just about to hit the 'Buy it now button' when I had an epiphany...
In light of this, I present my new spine tester, made from a set of kitchen scales, an ashtray, two blocks of wood, two pencils, some foreign coins and five pencil marks on the kitchen table:
- The amount of money that I was about to spend was not far away from the cost of a second hand commercial spine tester
- It would still only measure to 500 spine as that's what my dial gauge reads to
- That Bearpaw electronic spine tester, brilliant though the idea is, isn't actually doing a lot.
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Like the Bearpaw tester, you press the middle of the arrow down to the plinth which is set 0.5" below the bottom of the shaft:
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And read the number on the scales:
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And it has a major improvement over the Bearpaw unit as, thanks to the two extra pencil marks on the table, it works on 23" supports as well as 28" ones:
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It's not as good as the Bearpaw one as it doesn't read spine directly. I was going to develop a spreadsheet to work it out but in the end I decided that would be overkill as the equation wasn't complicated:
At 28": spine = 220,000 / weight on scale in gramsAt 23": spine = 396,929 / weight on scale in grams
Given that it's an experiment / prototype, it seemed to work pretty well, what with hexagonal pencils as supports rather than frictionless bearings, a 0.5" plinth that was pretty much just eyeballed for height, kitchen scales with a dodgy battery that is only precise to 5g, and test arrows that I couldn't be bothered to defletch:
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The one fly in the ointment was the last Cartel 500, but a bit of research revealed that Cartel do spines different, so there you go.
And the 1716s were crossed out as they were no-name Chinese ones that 1716 was always a guess for anyway, so I threw that reading away.
And if you're interested, here's a look into my brain when it's trying to work out the equations:
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