Spine tester

tabashir

Supporter
Supporter
...when supported at centres of 28" with a weight of 1.94 lb suspended from the middle. It used to be 26" centres and 2 lb, but that obviously had to be changed because it was almost sensible.
Beautifully put!
Many a true word hath been spoken in jest.
 

Del the Cat

Well-known member
Most spine measurement is comparative rather than absolute.
Here's my jig, it's easy to adjust the supports (for short flight arrows).
The weight is a spot calibrated bag of stones :)
The leverage gives good sensitivity.
spine tester
It should also be noted that the "modern" spine measurement method runs in the opposite direction to the old one and is less versatile in that it assumes a fixed distance between supports where the old method incorporates that into the calculation.
Del
 

dvd8n

Supporter
Supporter
AIUK Saviour
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 😭:cry:😭
Well, 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...
  • 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.
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:

IMG_20210310_115958.jpg

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:

IMG_20210310_142212.jpg

And read the number on the scales:
IMG_20210310_142230.jpg

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:

IMG_20210310_140245.jpg

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 grams​
At 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:

IMG_20210310_143734.jpg

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:

IMG_20210310_143800.jpg
 
Last edited:

Del the Cat

Well-known member
Well, 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...
  • 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.
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:

View attachment 8560

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:

View attachment 8561

And read the number on the scales:
View attachment 8562

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:

View attachment 8563

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 grams​
At 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:

View attachment 8564

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:

View attachment 8565
Excellent use of pencils, annotation and smiley faces :)
Del
 

dvd8n

Supporter
Supporter
AIUK Saviour
Just as a FYI, Cartel spines are the weight in grammes required to deflect the shaft by 20mm with the shaft supported at points 500mm apart. Which, hilariously, gives numbers that look like they may be Easton numbers, and values that look like they are compatible with Easton numbers, but are different enough in spine ratings to subtly **** you up.
 
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