In the past week it's been ugly cold so I added some complication to my simple spine tester. By scrounging I came up with a clothespin, an old thumb knurled bolt from a "glory jar", a toggle link made of a bent nail, two nylon ties, a bamboo skewer, a #6 machine screw and three washers, a piece of pine to hold the scale, a piece of cereal box cardboard to mark the scale on and a piece of poplar to bolt the clothespin to. By adding these to the two 1/2" dowels 26" apart on the sheld (aready there) I now have a direct reading spine scale that shows deflection in 1/20 of an inch graduations (0.0, 0.05, 0.10, 0.15 etc.) I can ballpark the in between values well enough for my purposes. For the deflection to spine values I downladed a table from Rose City Archery's website.

So, what's it look like?

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The time consuming part was calibrating the scale. First I moved the adjustment screw in the jaws of the clothespin until it was mid-range. (This will allow me to zero the scale for different diameter or tapered shafts . . .Ooooooo!). I used a vernier caliper and a pair of "T" pins. I set the first pin under the shaft without the 2# weight on as a zero mark. Then I measured down 1/10th of an inch and carefully placed a second "T" pin. Pulling the first pin and pushing the shaft down I then marked the scale. I repeated this until I had all the 1/10" graduations. Then I scientifically added the arc of movement on the scale by moving the clothespin around and ticking off the cardboard where the tip was. I measured 1/2 of those distances (Hey, they were evenly spaced at 0.9" between - I must have been close enough to accurate) to give me the 1/20" ticks.

You can see a few shafts I measured - right where they should be! Be sure to set the grain vertical with woodies (that gives the stiffest reading). Sounds obscene.

Two little bits that may not be obvious - I put a little piece of dowel under the clothespin so at rest it doesn't swing fully down. This makes it easier to lay a shaft in and will protect it from casual damage. The other is that the link is a "C" shaped with right angle bends. It's a finishing nail with a bit of balse to trap it to the clothespin. Free swinging; I silver-soldered a few turns of wire to it to trap it in place. The clothespin is bolted to a triangle of wood that is in turn screwed to the shelf. Just one screw so I could twist it to get the best clearance on the scale (close but not touching. The clothespin is held to the block by a #6 machine screw just threaded into the block after drilling a small pilot hole. One washer on the outer side and two inner gave good clearance.

There you have it. I've been spining arrows and getting some surprises . . . but mostly they're where I expected.

Enjoy.

PS - the original 2# weight goes at the 13" mark and is just an opened screw eye threaded into lead ingots. Once I was happy with the bamboo pointer I used Instant Glue to fix it to the clothespin. Also used that to strengthen the screw threads - with the screws out until it dries!

Thats just plain all right, love the zero adjustment.

Goo job, I like it.

Thanky. Working up a better defined scale for it now. I went through 40 shafts a few nights ago and had a few surprises it what were supposed to be spine matched groups. The zero feature makes all the difference - you could use a wood wedge in the clothespin jaws for the same adjustability.

One problem I see, it seems that your marks are evenly spaced on the scale? That's not how it works. Spine is based on a math formula [deflection divided into 26 = bow weight]. As the shafts get stiffer the marks are closer together and as the shaft weakens they move further apart. Example the deflection difference between 70# .371 and 75# .347 is only .024 but the difference between 30# .866 and 35#.742 the difference is 124. There is 6# difference in each of those shafts, but a huge difference is spread. And I'm not sure I like the clothespin idea, you might be getting some flexing from the 2# weight. Just some thoughts. Bob

Where can I get the formula for the proper spacing layout? Is the arc based on a circle or is it derived from the same formula?

Also, I thought standard was 28". Why would you space the arrow at 26"?

Stucky, wooden arrows are still measured using the AMO standard which called for measuring deflection by setting the arrow on rests spaced 26" apart and applying a 2# weight.

The synthetics are measured using the ASTM standard which calls for measuring deflection by setting the arrow on rests spaced 28" apart and applying a 1.94# weight.

As to WHY there are 2 standards, well, that is just one of those mysteries of life. Nobody really seems to know.

Very clever.

Rube Goldberg's got nothing on you!

Good job!

Just a thought. ....first off thank you for the great explanation and pics. Regardless of the scale graduations...are we not looking for shafts of near equal spine? I think this home brewed tester would do it! It's always about the journey! Your love of this sport shows. Thanks again.

Looks good you did a great job.My spine tester only has my various bows marked on my scale.I can't give you actual numbers as my scale is set to a master shaft.When I find a arrow that shoots as close to perfect as can be for a particular bow I spine all my arrows to match that.Numbers don't really come in to it for me but actual performance is what matters.In one way Bob is right but I am sure you would still get exceptable results.as long as you have some base figure to work off any variation could be taken into account.I just make my spine meters as I need them but I would be lost with out my master arrows .Yeah I also make simple balance scales to weigh my shafts too.my shafts are measured in coin weight.On average most of my footed shafts weigh 11 Australian 5 cent pieces .your meter looks awesome and in my opinion should serve you well. OSR

You have the marks correctly spaced. You area not reading spine, you are reading deflection. You then look at a scale that has deflection beside the corresponding spine rating. Some, if not most spine testers have such a double scale.

You are good to go, and nicely done, I say. I use a dial indicator. I think your setup would be easier to use than mine, but mine is easier to store, and it stays stored more than it is in use. :)

Jim

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