spine tester in PA

[mox1968]

hi guys I have built the spine tester mentioned in the last issue of PA magazine but hit a wall at the last fence making the scale!!I dont really follow the instructions there ,Im a bit lost as to how to mark out the upright marks from the bottom of the scale.I never really used inches as a decimal scale like that so not sure how to work the sizes over to a ruler or  other measuring device??

[Lombard]

Measure the horizontal line as specified in the article, then a vertical line at 90 degrees to that. Using the chart giving deflection values, you will need to multiply them by five, as the ratio is five to one on the needle. That is to say, (for the sake of easy math), if you hang the two pound weight on the shaft, and had one inch of deflection, the pointer would, from zero, register five inches of travel on the vertical line. So take those deflection values provided in the chart, multiply by five, then take that result and measure up the vertical line that amount for each of the values that you will be using.

[hillbilly61]

mox..Same here. Dave, I still don't understand  I guess I'm just a dumb ol hillbilly If all the marks on the scale are the same would'nt it be easy to say, from the bottom mark up 2" and every 1/4" above that, make another mark? Or something of that naturer?

[Lombard]

Yeah Mark, if the author had did as you describe, it would no doubt have simplified the scale for most folks. Take for another example, page sixty figure 5a of the June/July 2010 issue of PA, multiply .75 by 5 for a result of 3.75 inches. That 3.75 inches would be measured on the vertical line and a dot placed at that point. Now with an arrow in the supports with a two pound weight hung on the shaft deflecting the pointer to that dot, would indicate an arrow of approximately 30 pounds of spine. Another way to get this scale would be to scan the image and save it a jpg. Open in MS Paint, change the size there and print it out, and there you go. I am not all that computer savvy, so perhaps someone else can guide you through the enlargement of figure 6b on page 61 to workable portions. Otherwise, just do the math, and place the results on the  vertical line, thus making your own scale. 

[mox1968]

ok thanks lombard I think I have it now!!But I totally agree with mark would have been a lot easier to me to give me some sizes to mark off from the bottom of the vertical line.I been out of school for a lot of years now and find using a measuring tape comes more naturally now.

[hillbilly61]

  That makes more since. I'm usually pretty good at math. even teaching my daughter algebra, bit that one got me good. If you go by the 3.75 and increase the size in MS Paint, you should be able to measure the increments in between each mark and multiply by that amount. I think I'll try it today if I get to feeling better.

[mox1968]

tried it but it doesnt seem right ,i have a few shafts supposedly 40# but the spiner shows them at 25#!!!!mmmmm not sure what ive done here needs tweaking i think!!

[hillbilly61]

Let me ask this. If I have 1/2 dozen arrows that I know shootand group good for me, why can't I just make the tester. Then put the finished arrow on the tester, mark the spot the pointer goes to. I'm assuming that they will point to diff. marks ,but be within a reasonable amount of space apart. Then use this mark as your target spot for the shafts you make? Just a thought.

[Genghis]

Perfect hillbilly - this is one of the principles of understanding spine.

You don't actually need to measure spine against a scale if you have a known arrow to compare with - just make a mark and use it to find other arrows that match.

Scaled spine testers come in handy when you have more than one bow needing differently spined arrows or build arrows for others - then you need a marked scale.