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?
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!
Topic: Less simple but still cheap spine tester. (Read 156 times)
