Primitive Archer
Main Discussion Area => Arrows => Topic started by: wolfsire on November 14, 2008, 02:50:02 pm
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I have downloaded instructions for an adjustable spine tester that seem really good, but I do not want to build it right now with the limited time I have. Instead, I’m looking for something really simple and fast.
I have a small bow 35lb at 20” and want small arrows (this time), so I’m thinking 30lb at 21”. If I put 2 nails 20” apart, drawing a straight line between them, and measure from the mid point the downward deflection with a 1lbs weight, what distance will get me 35lbs? What about 2 lbs? I think 35lbs that would be the weight I want given that the extra inch will reduce my spine by 5lbs. 2lbs would be more accurate, but 1 would be safer on the light arrows.
I have yet to find a formula and I do not want to build and use a meter that are are based on forumula. I want to draw a second line to mark the correct deflection and eyeball it.
Thanks in advance for your help.
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Well to just use it for this bow and arrow set.. I would say find a shaft that shoots well off the bow and use the system you suggested and hang what ever weight you want on it mark it. then just use it as your reference point for the rest..
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With the nails 26" apart, a 2# weight and reference arrows, David's method is almost as good as any. You can use it for the arrows for the kids bow but also any bows you shoot. Pat
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Thank you gentlemen, your comments are helpful, but still leave me in need of more.
Regarding copying a shaft that shoots well, I will do that, but after I have a working spine to begin with. The initial problem with this method is that I am almost a completely incompetent archer. Right now I am all over the place, so I cannot find a shaft that shoots well. Once I have some that I know are the same in the ball park, I can work on my from, develop some consistency, fine tune that by judging spine up or down based on missing left v. right, then coping as you suggest the most appropriate spine.
Regarding, 26" with 2lbs, I’m happy to work with that if I can. But I do not quite now how. Jim Hills' table for that says to get a 26" arrow to spine at 35lbs with a 2lb weight, you want a deflection of .743. If that number is not a distance in inches, then I do not know what it is. I could make an arrow 26" and put 2 lbs on it. That will give me both a distance and an arc. I might be able to do something with that, but I am not sure what.
If we could add 5 inches to a 21” arrow spined at 35, with 5lbs per inch, then the longer arrow should then spine at 10lbs. I do not know what to do with that. Hill’s table does not go that low. I could not spine at 26” arrow at 10lbs then cut it down to 21”.
If length/deflection=spine then 20”/deflection=35lbs gives me deflection= .58 or 37/64. I can measure that if it is in inches. But I do not know if it is. Is it only good for 2 lbs? If I use 1lbs would that be 18.5/64"?
Or is this formula only good for 26” and 2lbs and 5lbs/1” only as estimate that works on the margins?
Thanks again.
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Modern arrows are spined using a 28" arrow with a 125gr point. The spine tester's uprights are spaced 26" apart. For each inch under 28" you can add 5# of spine weight. My spine tester is my version of James Hill's tester with a dial indicator.
Check out http://www.jamesmhill.com/spine_tester.html. He has all the info you need to make one for very little money.
With kids arrows I start with a small shaft(5/16) and cut it longer than the draw(sometimes as much as 28") and reduce the length until I find what shoots best.
Pat
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I cheated with my home made spine tester.
On an old 30" cabinet door, I drove one nail for the arrow knok end at one edge of the door, a pivot point 10" from that. Made a 2# weight with an old leather pouch and some bird shot. (could use sand too)
Went to a local archery shop and picked up POC arrow shafts spined at 5# increments.
Back home, I simply lodged the knok end under the nail, rested the shaft over the pivot, hung the weight at a pre-marked 28" on the shaft and traced the curve of the shaft along the bottom edge.
Repeat that with all the shafts I had bought and I was done. No moving parts, no formulae, no sweat.
Total cost was for the POC shafts at a couple bucks each. I keep them for control shafts.
I spine all my arrows on this now, every thing from cane/bamboo to POC, maple etc. even my shoot shafts of Ocean Spray and Syringa get to visit this simple little cabinet door spine tester.
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Pat the Link dont work......... ???
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Wolfsire,measuring spine is a simple procedure ,that can be accurately done with the simplest of equipment.
Just as the others said; drive 2 nails,26" apart,horizontally into a shop wall,or the edge of a shelf. Set the arrow across the nails. Halfway down the shaft,mark either the top or bottom edge of the arrow.Now ,hang a 2 # weight in the center of the shaft,then mark the new position of the deflected arrow shaft. Now,measure this distance in inches. Say it deflects 3/8". 26 divided by .375= 70.27# of spine .Nothing to it. God Bless
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Mike, put an "underscore" between "spine" and "tester" ( spine_tester )
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Try this one Mike. http://www.jamesmhill.com/Spine_Tester.html
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Thanks Justin.....works now.....Pat that is a pretty complex setup....but cool!!!
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Mike, it is pretty simple. If I can build one anyone can. The dial indicator cost about $10 - $15... everything was found. Here are a few pics of mine.
[attachment deleted by admin]
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...well, I guess I did buy a few other parts. ;D
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OK.....so now I have another Project!!!!
:P
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I have a small bow 35lb at 20” and want small arrows (this time), so I’m thinking 30lb at 21”. If I put 2 nails 20” apart, drawing a straight line between them, and measure from the mid point the downward deflection with a 1lbs weight, what distance will get me 35lbs? What about 2 lbs? I think 35lbs that would be the weight I want given that the extra inch will reduce my spine by 5lbs. 2lbs would be more accurate, but 1 would be safer on the light arrows.
Wolfsire, I know exactly what you are talking about. I have the same issue with my short bows/arrows and the bows/arrows I make for my children.
The question seems simple enough.....but the answer is NOT.
First off, the existing charts were made by trial and error...hundreds, probably thousands of arrows were measured for spine to get the results seen on the charts. In order to get you the info you need, an expert archer with a 35lb bow drawing 20" would need to spine several 21" arrows (at 1lb and also at 2lb) and then get the averages.
OK, you would now have your distance. The trouble with just having the distance is that you need perfect arrows in order to spine them with just two nails, a weight, and a distance. If your arrows are not perfectly straight, you would need to "zero" the center each time and then measure the distance. If you have a way to adjust your little distance thingy, then you're fine.
Another thing is that the distance we are talking about is probably about a quarter inch (using a 1lb weight). Even 1/32" of an inch at this distance could mean a significant difference in spine. Eyeballing the distance would not be accurate enough.
I wish I had the type of chart you are looking for....I need one myself. Since I haven't had the time to develop such a chart, I've had to get good at making arrows that fly well without the spine chart. I've had to become an expert at "bareshafting" my arrows.
Hope this helps. ;D
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thank you all, and Jackcrafty in particuar ...
I understand why you are saying, but eyeballing is going to have to do ... and my shoots are not 100% straight. I will have to work on making them straighter and eyeballing to 1/64 the best that I can ... maybe a tiny level ... If I feel comfortable with 2lbs after some tests, I will go to that for more accuacy.
Ultimately my goal is to have arrows I can have confidence in, so that I can spot errors in my perfomance. This will get me in better range than the unspined unweighed floating (read inconsistant at 24 inche arrows) anchor that I have been working with. If I have a set that are the same at 20 or 21 inches (all the same, Im still debating length) of 350 grain and 30-35 lbs (again the same as much as possible), Ill have a basis to judge my ability with minimization of arrow related errors.
I am sure they will not be 100% the same, but if I get consistancy, then maybe I can copy the best of the lot to tune.
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The spine tester and chart we are dealing with follows industry standards. We, as primitive archer, are not dealing with industry standards or materials that are standardized. For each of us it is either guess or figure out what will work for me.
Somehow, primitive man figured out how to do it!...well, they did it because they had to. ;) Sometimes it is hard for me(personally) to come up with solutions because my brain is cluttered with modern stuff and I'm not hungry enough to have to figure things like this out. Eventually I can but my life doesn't depend on it. (I'm having the same trouble with the survival bow)
I think, having a known distance to bridge and a known weight to suspend from that bridge, the resulting deflection is the best way to figure spine if you have a known value to work with...but also, I think that sometimes we try to make too much of a relatively simple matter. That is just the nature of modern man. Pat
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for a bow of that weight and draw just pick up some 1/4" dowels . i recommend plastic nocks for em. those little suckers will fly like lightning out of the bow. my kids shoot em out of 20-30 pound bows and they are great. peace