<P>There is a link to a chart I built where you can adjust it to any length shaft, just change the shaft length number to whatever you like...26.75, 32.25, ect.......<BR><BR><A href="http://onemississipp.googlepages.com/spineweight.htm" target=_blank target=_blank>http://onemississipp.googlepages.com/spineweight.htm</A> <BR><BR>This way you can make a spine tester the length of the shafts you shoot.</P>
Brilliant! <br>Now I'll have to whip up a sweet little spine tester for my new shafts I just turned. <br><br>What do you guys use for the 2lb weight? I'm assuming that it has to be damn near <b><u>EXACTLY</u></b> 2lbs for this chart to be accurate.<br><br>
Brendon,<br> I would try to get it as close as possible to 2 lbs as possible. Some people use large bolts with washers. I'll try to find some pics, I'm working on one now and will post pics when it is complete.<br><br>The thing with arrow spine, is there is not really a standard set. I mean if you order arrows from several different places that are spined at 45#, and you tested them they would more than likely be different.<br><br>If you look at the spine charts from different vendors they all very from one another.<br><br>So to have your own spine tester and finding the deflection/spine your bow likes would help in making and possibliy buying arrows. Where instead of ordering a spine weight you could maybe, see how they measure their spine weight and then ask for a certain deflection, for example .423.<br><br>Hope that helps. <br><br><br>
<P>Chart is a blank page here.</P>
Sorry about that Roy.<BR><BR>Are you using a windows machine?<BR><BR>The chart really isn't that good as I have come to learn more about arrow spine.<BR><BR><BR>"Spine" is one of those terms which means different things in different context.<BR><BR><B>STATIC SPINE</B> is the stiffness of the arrow and its resistance to bending. To determine statice spine, the arrow is supported a two points a known distance apart and a force is applied to the center of the distance, usually through a weight. The amount of displacement of the center point, how far it drops, determines the spine. Arrows with a high spine will not sag as much as arrows with a low spine.<BR>The factor which determines the spine is the stiffness of the materials in the shaft and the geometry of the shaft. In multi-layered arrows (carbon, aluminum, etc.) the bonding materials also contribute. The inside diameter, the cross-section shape, the thickness of the material all contributes to the Static Spine.<BR>The Spine never changes unless the arrow is broken somehow.<BR><BR><B>DYNAMIC SPINE</B> is how much the arrow does bend when fired. This depends upon stiffness (Static Spine), string force, fletching, nock weights, etc.) "Weak" and "Stiffness" are often used in terms of Dynamic Spine. <BR>It is more difficult to determine Dynamic Spine than Static Spine because all the simple formulas don't work with such a massive force acting down the shaft. Consulting a Machinery's Handbook or other Engineering manual will give beam formulas to determine Static Spine, but when dealing with a large compressive force, "all bets are off."<BR><BR><BR><BR>So in all the Static Spine Tester really only gets a person in the ball park to begin testing and dialing in on Dynamic spine (this is the real deal).<BR><BR>
formula for spine is: 26 / Deflection<BR><BR>I used 26 as an example, becuase that number could change. 26 is the distance between support positions on the spine tester.<BR><BR>You could build a spine tester with 30" between supports and then the formula would be 30/deflection.<BR><BR>So if the spine tester was set a 30" and you had a shaft that deflected 0.100 under a 2lb weight at center, the <B>Static Spine</B> of that shaft would be 300lbs.<BR><BR>Hope that helps some Roy.<BR><BR>I'm still learning here.....<BR>
<P>Yes windows XP for Home.</P>
I found one on the net at <A href="http://www.archers-friend.com/archers-friend-spine-testers.html" target=_blank>http://www.archers-friend.com/archers-friend-spine-testers.html</A> . It is made using a Dial Indicator. I built it and it works great. Was simple to make too. Bought the Dial Indicator offin E-bay fer $10. The rest from Home Depot. <br><br>TheWildCat<br>
nice sharing i don't ever see this kind of calculator,..nice formula,..