Straightarrow

Several weeks back, there was a discussion on spine testers that stimulated me to make one. It took about 5 weeks to receive the dial indicator that I ordered, so it took awhile to get to the project. Once the indicator came in, it took about 2 hours to construct the tester. So far, I've only played with it, putting in arrows that were already cut. It seems to work very well. I plan on making up a new dozen within the next few days to put the tester through it's paces.

I used Jim Hill's Spine Tester as a guide, with a few adjustments.

Please excuse the mess.


I decided to use wood end supports, so I could make a finer adjustment when trying to get the arrow to just slightly depress the dial indicator, before the weight is applied. I did this by mounting cabinet door rollers (which have an easily adjustable height), on to the side supports. I could then set the supports next to the base, without actually attaching them, just to test the height. I made the supports a bit long and them shaved off small amounts with a table saw to end up with exactly the correct height.

The cabinet rollers:


I found an order to construction that worked particularly well. First cut the base to the length of tester, plus width of rollers. I used 28" as the space between the rollers. It seems Easton used this when testing modern arrows. The weight is 1.94 lbs.

I then cut a dado in the exact center, to accept the 6" angle bracket. I mounted the angle bracket and then attached the extention with the eye bolts to accept the weight. I then figured an approximate center from the edge of the base to the center of the eye bolts. I used this measurement to mount the rollers the correct distance from the edge of the end supports.

The dial indicator was attaced to it's bracket, and then was put into approximately the correct position. It was attached to the base with only one screw at this point.


This is where the fine adjustments come in. I used a bar clamp to keep the supports in position while I fiddled with getting the height of the supports correct, and the exact position of the dial indicator right. With an arrow in place, I moved the dial indicator until it's point was in the exact center of the arrow. I then attached the second screw to it's bracket to fix the dial indicator in it's final, correct position.

Once the indicator was permantely mounted, I started shaving off the bottoms of the supports, until the exact correct height was obtained. Once this is correct (and the clamp still on), glue and screw.

I made a spine chart based on the 28" length and put a clear expoxy over the whole base to keep the chart permanently in view, and protected.


I have the advantage of owning an electronic scale, so I was able to get the weight close to exact (not that it's very important). When buying washers I got extras, because they were variable thicknesses and I could use different combinations to get different weights. I found a combination that came to 1.94 lbs. I set the bolt on a table, as in the photo, and then added a bit of epoxy between the bolt and the washers. It turned out as a nice solid piece.


I highly recommend making your own spine tester. It was a very easy project. I had about $35 into it of which half was the dial indicator. You can save a bit of money by eliminating the main bracket and using a wood support. I didn't think of the wood support until after I was done, but I think it would have not only been cheaper but would have made mounting and adjusting the eye bolts much easier. The 3/4" x 8" bolt and washers, and brackets are more expensive than one would think. I would imagine that you could come up with something that would work just as well and much cheaper.

I hope this helps anyone wanting to make one.

BobCo19-65

Very nice. What was the total $$$$ spent?

Buck_Slayer

There ya go. bottom of his post

Straightarrow

I had a chance to play with it last night, and I received some interesting results, but unfortunately, I don't know how to interpret them. I realized I didn't know what was considered poor variance and what was acceptable.

I first tested a few aluminums to see how much a consistant material would vary. They were within .003 on all sides (I know there are no sides on a round arrow, but in this test I pretended there were four).

I then tested half dozen Beman ICS 340 Hunters. Interesting that they hovered right around.340 on my spine tester, which gave me confidence that I was at least close with my measurements when building it. 2 of the 6 were within .003 on all sides, 2 were within .006 and the other 2 varied around .012

Next were some Easton Lightspeed 340s. These also hovered in the .340 area of the dial indicator. One of these was virtually identical on all sides. The other five were all within .005. I was impressed.

I then decided to test a full dozen Goldtip 7595 Hunters. Most of these spined in the .325-.330 area. A bit stiffer than the others, even though I believe they're supposed to be in the .340 range. This left me wondering if my tester was off, or if the Gold Tips were off. Maybe they not supposed to be .340, I'm not sure. Out of the dozen, there were 3 that were within .003 on all sides, 3 that were within .008, 5 that were within .015, and one that was off by .026. It looks like there will be at least 6 decent arrows in this dozen. The others will probably practice arrows.

Any input on what's considered good and what isn't is appreciated.

I marked the weak side on all dozen of the Gold Tips, which I'm going to buy and fletch. I've decided to put the cock fletch on this mark. I will then test them with broadheads to see how they fly as a group. One thing I realized after doing this, is that if the arrow shaft isn't at least 28.75" when built, the tester won't be useful in checking spine down the road. Since I want to be able to do that, I will cut them at 29", even though I normally use a 28.25" shaft.

Another question popped up while doing this. Some seemed consistant on 3 sides with one weak side and some seemed consistant on 3 sides with one strong side. In the latter group, it was difficult determining the weak side, because the other 3 sides were close. I also discovered that most weak sides were 90 degrees to the strongest side, so I'm thinking that on these questionable ones, I'll designate the weak side 90 degrees to the strongest one. Any suggestions here are also appreciated.

AllenRead

SA,

That's a great project. It's probably as accurate and certainly a lot more economical than the commercial models available. I've been considering one myself from Hill's plans.

I appreciate your note that the arrows have to be 28.75". Since I shoot 28" arrows, you just saved me from a mistake. Thanks!

If you built it again, would you make it shorter for shorter arrows?

Great post!
Thanks
Allen

Straightarrow

AllenRead,

I wanted to make it according to a standard. The AMO standard is 26", but is mostly used by those making traditional wooden arrows. Apparently Easton established the 28" and 1.94 lb standard for modern arrows, or at least for today's commerical products. I believe following a standard is important when making wooden arrows for someone else. If they order a particular spine, I'm sure they expect to get just that.

For personal use, or when using it to compare arrows with each other, I see no reason to be stuck on a particular length. The 26" length would work for many more people. You would have to careful to not go too short, or you would have to increase the weight to get much deflection on real stiff shafts.

Straightarrow

TTT for Chief

ChiefHeadhunter

Thanks!

-Chief