I am in the process of constructing my protractor type spine tester and I have a problem. One site ...poekoelan's CHEAP, EASY, ACCURATE SPINE TESTER....from this forum gives the following chart for conversion from degrees to spine....
30-35 lbs 60-48 degrees
35-40 lbs 48-40.5 degrees
40-45 lbs 40.5-35.25 degrees
45-50 lbs 32.25-31.25 degrees ......and so forth,
Another site from Primitive Archer, http://www.geocities.com/archeryrob/pa_spine_tester.htm, gives the following chart...
30-35 lbs 59-90 degrees
35-40 lbs 49-59 degrees
40-45 lbs 41-49 degrees
45-50 lbs 35-41 degrees ......and so forth
You can see that the charts don't agree....the ranges for the degrees are approx. the same for both charts, but they are shifted by 5 lbs. between the two charts. Also, it seems to me, if you are trying for an arrow spined for say 40 lbs., on the first chart you are looking for 40.5 degrees of deflection and on the second chart you are looking for 59 degrees of deflection.
Thanks for your help. dj
Sorry guys, that link to the second chart doesn't seem to work. However those are the correct conversions from that chart.
I got plans from The bowyers den(I believe), the second set of plans on the site. It came witha printable scale....saved a ton of aggrevation.
Just ran across this and I have to go to work now. When I get home I will explain the differences.
Ok. Back from work.
dj,
If you look at the web page that you are talking about, there are actually MULTIPLE charts for different draw lengths and they all differ by five pounds. More on that later, but this is one thing I don't like about the plans on that site or the orginal plans in PA magazine. These charts can be very confusing for beginners if they aren't very knowledglable about spine. The author of the article did a great job in explaining how to make this thing, but not a very good job as far as how to read it and use it, IMO.
Before I go any further, let me say I have confidence in my chart for two reasons. Number one: I based it on the AMO standards. You can find the AMO standards on the Rose City website. Number two: I tested it against aluminum arrows that were spined on a good factory spine tester and my chart jived. See the Arrows by Kelly website for the spine values of different aluminum arrows.
There are two kinds of spine. Static and dynamic. Static spine is the measurement you get when you put an arrow on a spine tester. Dynamic spine is how the arrow actually acts when it is shot. If you have a 26" arrow and a 32" arrow that are both spined 50lbs, they will fly differently when shot. In other words, their dynamic spine will be different. BUT..they will both still read 50lbs on the spine tester.
There is an old rule of thumb for determing spine. For every inch of drawlength over 28", add five pounds of spine. For every inch of drawlength under 28", subtract five pounds of spine. I believe the author was trying to take this into consideration when he came up with multiple charts for different drawlengths. But he seems to have gotten that wrong because the one chart that DOES jive with the AMO standards is the chart for a 26" draw length, when it should be the one for a 28" draw length.
All of this puzzled me years back when I built one of these spine testers. Plus...I wanted to be able read arrows that were stiffer and weaker than the ones he has in his charts. His chart only goes up to 70lbs, and it keeps dropping the longer the drawlength is. He tells you how he came up with these values, but you have to know something about triginometry in order to understand what he is saying. I didn't know anything about trig, but my brother did so I went to him.
He also found the author's methods confusing. He asked me if I had the AMO standards in hundredths of an inch. I said I did and he said it will be real easy to figure out. He showed me how to do it on a scientific calculator and I did it. After I did it, I found out that my values converted from the AMO standards lined up with the author's values for a 26" draw length. If you would like to do it yourself, shoot me a pm. I can tell you how to spine every arrow to the pound ( not just the five pound groups ) if you are interested. It's very easy. All you need is a scientific calculator and you probably have one on your computer.
Out of all the homemade spine tester plans, this is the simplest and most inexpensive one to make and it's just as accurate as the other types. I believe it would be more popular if the charts in the article weren't so limited and confusing. I tried to simplify the chart by making it jive with AMO standards and by expanding it a bit.
If you are interested in how I did it, shoot me a pm or email me at poekoelan75@yahoo.com.
Hope this clears up some confusion.
Austin
CORRECTION...the chart on the website that does jive with AMO standards is the one for a 27" draw, but even it is off a bit because the author didn't use the AMO standards in hundredths of an inch, he rounded AMO values off before he converted them. I didn't.
Poekoelan......Thanks so much for your interest in my confusion and your effort, at 11:37 at night after working a full shift, to help me out. I know about the two types of spine and did wonder about the multiple charts on the website but it just didn't dawn on me that the one was trying to account for the other. I appreciate the offer for the trig lesson, but I think I'll pass. I got my tester made yesterday.....mounted it on the wall over my work bench at eye level instead of letting it be a freestanding unit. In my shop, every inch of space is valuable. Now, thanks to you, I'm ready to use it!!!!!!
Mine is finished as well, and I have to admit, it do work ! Later on down the road I would'nt mind getting a "store bought" version, but this one will work just fine for the time being. I tested mine with about 30 shafts, which where know spine weights. The hardest part, was all the trips to the post office to weigh the weight, lol!!!
I'll post some pics later on.
Thanks to Austin for all the help !! Another part of what makes this the BEST Traditional site in the universe.
Jerald
No problem guys. Enjoy the device and have fun. I'm glad you guys like it. When I built mine, I was confused and I didn't know as much about spine as I do now. And I was always a little aggrivated about those original charts until years later when my brother showed me what to do about it. It was so simple, just press one key on a calculator and the actual article made it sound so confusing. Even my brother who DOES know something about trig thought it could have been explained alot simpler.
But I can't totally fault the guy, he came with a very cool MacGyver like design that only costs a few dollars to make. Post some pics. Wall mounted sounds like a cool new twist on it.
Austin
Hi Austin,
I sent you an email. I'll also follow this thread, if you get enough requests, you can respond here. I would love to see those calculations. Trigonometry was not my favorite section of math but this might be a new inspiration.
Thanks,
Aram
Aram I sent you an email. But here is the short answer in case anyone is interested. Here is how did it on the scientific calculator that is on my computer. Enter the AMO deflection in the calculator. Check the invert box. Click the sine button. And that's it. You'll have to round it off to the nearest quarter degree. But I didn't round off the original AMO values like the author did. That's why his 27" chart is slightly different than my chart.
Austin
Hello Guys , I got in a little late on all this and as I have been interested in getting a spinetester can someone give me directions to the site you are talking about ? I would like to make one , thanks , Fred
this will be my first attempt at posting pics on this site, so bear with me....
As I said before, my small shop has to wear many hats and space is at a premium, so this spine tester is mounted on the wall above my workbench at eye level.....the arrow shaft is held by 2 coffee cup hooks......the weight is an empty pvc solvent can filled with lead fishing weights.
(http://i163.photobucket.com/albums/t298/don57/DSCN1719.jpg)
(http://i163.photobucket.com/albums/t298/don57/DSCN1718.jpg)
(http://i163.photobucket.com/albums/t298/don57/DSCN1716.jpg)
Dj, Very slick adaptation. I like it. The Ace Spine master has nothing on you! Greyfox, do a search on pow wow for cheap easy accurate spine tester.
Thanks , !!Warning!! I will probably have questions , Fred
Here are a few photos of the one I made. I have cheap camera, phots are not all that great.
URL=http://good-times.webshots.com/photo/2146354030100570538hhVuje] (http://thumb18.webshots.net/t/53/453/3/54/3/2146354030100570538hhVuje_th.jpg)[/URL]
(http://thumb18.webshots.net/t/57/757/5/59/15/2638559150100570538ekCRiQ_th.jpg) (http://good-times.webshots.com/photo/2638559150100570538ekCRiQ)
Looks almost just like mine, but nicer! I had a heck of a time trying to find a 360 protractor so I just ended up putting two 180s together. A single 180 will work fine, but I think a 360 eliminates some back and forth play. Where did you get your 360?
Austin
I bought the protractor from an Arts and Crafts store, I think is was around $3.00.
It's all walnut with brass hardware. I think I have about $10.00 in the whole thing, lumber come off the job, the lead I had, it was a fun little project. I like the idea of a wall mount, may add that to this one, I have some more of that walnut flooring left.
Guys,
This is great information, i'll have to get the link to the building of the spine tester that was posted a couple of days ago. Nice Work by all.
Do single tapered shafts, differe in spine from paralell????
http://tradgang.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=1;t=040744
I was just searching around the net for AMO standards, and I think I found out why the orginal charts for this spine tester were so confusing. Check this out..
http://archerysearch.com/publications/AmoStandards.pdf
This looks just like the original protractor charts...values rounded off to hundredths instead of thousandths, different values for different draw lengths, values only going up to 70lbs. Not only that, but there are different values for target arrows vs feild/hunting arrows. Talk about confusing. If this is what the author had to work with, I think he did a pretty good job.
Here is what I based my chart on...
http://www.rosecityarchery.com/amospine.html
The second chart simpler. But BOTH of these web pages are supposed to be AMO standards. Makes you wonder, when you buy a dozen shafts spined at 55/60, what values and what charts are they going by??? I thought AMO standards were supposed to be standard, LOL.
Austin
Gator, I've never used tapered shafts yet, but I've heard from some that the spine will change once they are tapered and I've heard from others that they hardly change at all. Maybe someone with more experience will come along and answer that one.