I wanted to build a spine tester but didn't want to spend the $$ for a dial indicator. Thought about one with a pointer arm but that seemed more complicated to build and not as accurate. I already had a digital caliper (never seen one using a caliper) so I thought I would try it. It is simple to build, easy to use and very accurate. Though I would share encase anyone would like to build one. Paul

Hello Paul,

I think your design is a good one! Simple to the core which is what I like best. The weight is totally tunable and the caliper is easy to zero out initially for each shaft. As long as the caliper does not provide any "extra" force down when taking the final deflection reading then it should be extremely accurate (certainly more accurate than it needs to be!)

I made a similar setup using a dial indicator instead of the caliper and it has proven itself to be accurate and very valuable when build wood arrows.

Just to double check your setup, I would reccomend checking a wide spine range of aluminum shafts to their known published deflection data. If your setup is within +/- 0.005" on a 1816 through a 2219 then you are good to go!

-Stu

Paul, Looks pretty functional to me..The pill bottle I assume has 2#s of lead shot or something in it and a hook to hang on the shaft? 26" centers for spining wood shafts?

So HOW do you take the deflection measurement given by the inexpensive caliper that you open until it touches the shaft deflected and convert that to spine of the shaft? Jim

dire wolf

Yes I used an electronic scale to add lead shot to the pill bottle to reach exactly 2#. I lower the depth probe of the caliper to just touch the shaft and then zero the caliper. Add the weight and adjust the caliper to just touch the shaft again and read the distance on the caliper. To convert that distance to spine I downloaded a chart off the inernet to make it easier. You could create your own chart with a spreadsheet by using the formula: 26 (the distance between the supports) / the deflection of the shaft = spine. Example 26/0.347=75# spine.

Jim, That's the easy part. Just take the measured deflection and divide it into 26 to get the spine rating in pounds for a 28" shaft. An example would be that if the measured deflection is .500 then dividing that into 26 will give an answer of 52. So that shaft would have a spine rating of 52# at 28".

moebow, Thanks..that IS pretty simple..:) Stu, others: Do arrow smiths measure spine for carbons differently than we have done for woods over the years?Jim

Yes they do. For some reason, they went to 28" centers for shaft support and used a 1.94# weight. I don't think the arithmetic is as simple and I believe that is why the Easton charts always end up with a stiffer spine than we want.

Ahh yes..building in job security and making new archers dependant on others by garbelling up a time proven system..:) Jim

As the story goes, Easton changed to the 28" and 1.94# weight because an employee in the plant several years a go decided he should check the weight they were using on their spine tester which was 26" centers and found the weight to be 1.94# instead of 2#, (in the real world that .06# difference really didn't make enough difference to worry about). This presumedly caused panic within the ranks and a new system was suggested to ATA, of which Jim Easton was President at the time. In those days most everything was compound so the change really had no adverse effect, as the strike plate depth is easly changed on a wheel or cam bow. The problem started when Trad archery had its resurgence. The new standard just doesn't work for a trad bow. If I were shooting carbon arrows I would spine them on the old system, spine is spine and the old system will work with any shaft material. The only problem will be the lack of different spines in the carbon world, so you will still have to play with arrow length and point weight, but it will give you a starting point closer to what you need. Have you noticed how few aluminum spines are now available today as opposed to 20 years ago, that has made it much more cost effective to Easton. Folks its all about dollars in there pocket, not about whats best for the archer or archery. Bob

I like it. I can't tell from the photo -- How is the caliper mounted to the base?

Scott Its a magnetic caliper base. I got it from Rockler. Part# 41424. $9.99. I mounted a small steel plate to the caliper stand and just attach the caliper with the magnetic base. Paul

Through Harbor Frieght I got a dial indicator for $10.00.

Bob, Thank you for the history, I always wondered about the "silly-ness." I have always used my old system spine tester on wood and aluminum shafts. I've really never gotten into carbon, they just seem too complicated compared to the old 5# rule of thumb that I grew up with. Yep, it's all about the $$$$$

OK here's an even cheaper way to get the spine you want.Find an arrow shaft that shoots well for you. Put 2 nails in the edge of a workbench or such anywhere from 26 to 28 inches apart. Put an arrow on the 2 nails and place a 2# weight in the middle of the shaft. The pill bottle with shot in it is a great method. Put a hook in the top to hang it on the shaft.Now drive in another nail at the bottom of the bent shaft. Viola!!! You can now check spine on shafts against the arrow that flew well!!!! Works great for seperating woodies. FRJ

I made one with a pointer and a curved deflection scale w/lb. Equivelents for zero cash. Just scrap laying around. Not that hard. Full instuctions for building it were in an early TBM. Back when they used to have how-to-do-it articles. Very accurate!

I spine ALL arrow materials at 26" with 2 lbs. The OLD way! Deflection is deflection,and that's all I need to know to get the right spine. They can have their NEW system.It's an innaccurate joke!

I really like the idea of using the dial caliper,in place of dial indicator,because its a measuring device that everyone should own anyway.

If you have already registered, please

sign in now

For new registrations

Click Here