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Old 02-25-2018, 05:01 PM   #1
enewman
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Default Info for people that spine test there arrows

VERIFYING ARROW SPINE
When we look at static spine of a shaft we go off IBO measurements. This standard way to measure is supporting an arrow at 28 inches with an indicator setting at 14 inches from each support. Then an 880-gram weight is hung at this center point of shaft. The reading on the indicator translate to the static spine of the shaft. This means if we get a deflection reading is .325 then the static spine is 325.
Doing this test there are things we do not know from the manufactures. Where is the indicator set for movement? With a ram tester it is fixed so this is set if using this tester. Now what indicator are the using because this will make a difference.
Letís look at why it makes a difference. I have three different indicators. Two digitals, a Pittsburgh and a Shars, and the one mechanical is a Kurt. The mechanical, I have removed the spring, so the indicator reacts faster.
The Kurt indicator when set at .5 travel on a gram scale shows 27.1g. the Shars set at .5 travel shows 151.9g. and the Pittsburgh at .5 travel read 112g.
What does this mean? We look at the IBO measurement again. The weight to spine check is 880g. so when testing with my three indicators we have three different outcomes. The mechanical adds 27.1g. meaning now Iíve got a total of 907.1g. on arrow the 112g. is putting a total of 992g. on the arrow and the 151.9 indicator is applying 1031.9g. on the shaft. Its easy to see that we are going to get a difference.
I ran a test on an aluminum 2114 shaft. I used an aluminum arrow for this test due to the consistency of how an aluminum arrow is built.
SET UP.
My ram test allows me to move my indicator up and down so when I tested with the Shars I zeroed the tester. I then moved tester down till it read. 525 while on the arrow. This will be my set point for the other two indicators.
TEST RESULTS.
Testing the 2114 shaft with the Kurt indicator the spine is .512. the Pittsburgh displays .480. the Shars displays .465. All three indicators so, as you can see there is a difference of .047 from the two extremes. According to the charts a 2114 aluminum arrow is a 510 static spine.
WHAT DOES THIS MEAN.
We can now see depending on what indicator we use will affect the outcome. Depending on spring tension in the indicator and how much travel we set the indicator at will also determine the outcome. With out knowing what indicator the manufactures use and how far they have set up the indicator for travel then our static spine reading can be off.
HOW IMPOTANT IS SPINE
With what Iíve seen testing. I donít look so much at the static spine. Unless a manufacture is welling to give us the information on what tester and indicator with set up. There is know way of being very accurate. What I look at when spine testing is consistency between the shafts.
2018 EWN
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Old 02-25-2018, 06:02 PM   #2
muddyfuzzy
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See ASTM F2031-05 which should cover the associated acceptable variation in devices, their accuracy and allowable deviations.


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Old 02-25-2018, 08:20 PM   #3
enewman
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Quote:
Originally Posted by muddyfuzzy View Post
See ASTM F2031-05 which should cover the associated acceptable variation in devices, their accuracy and allowable deviations.


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For $41 to look at.
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Old 02-25-2018, 08:24 PM   #4
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The price of knowledge my friend! You can probably find a bootleg fairly easy, youíre a smart guy I have faith in you!


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Old 02-25-2018, 08:26 PM   #5
enewman
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Originally Posted by muddyfuzzy View Post
The price of knowledge my friend! You can probably find a bootleg fairly easy, youíre a smart guy I have faith in you!


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Iím looking. But what Iím afraid itís about is how we test. That I know. But with three different indicators one with no spring and the other two have springs but different tension. This is a problem. As you can see in my post
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