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?
(http://img.photobucket.com/albums/v169/Stumpkiller/Bowhunting/HPIM2040.jpg)
(http://img.photobucket.com/albums/v169/Stumpkiller/Bowhunting/HPIM2042.jpg)
(http://img.photobucket.com/albums/v169/Stumpkiller/Bowhunting/HPIM2043.jpg)
(http://img.photobucket.com/albums/v169/Stumpkiller/Bowhunting/HPIM2047.jpg)
(http://img.photobucket.com/albums/v169/Stumpkiller/Bowhunting/HPIM2045.jpg)
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!
Nice work McGyver! That thing looks rock solid! Thanks for the how to.
amazing! nice piece of work
That is pretty cool! Thanks for sharing it with us. :thumbsup:
Where's your pipe? :D
(http://img.photobucket.com/albums/v169/Stumpkiller/Bowhunting/HPIM2048.jpg)
Nice piece of work! :thumbsup: :thumbsup: