How To Make a Spine Tester

By Sam Harper

Some other spine testers

When I was on line trying to figure out what kind of spine tester to do for my build along, there were three criteria I looked for:

1. Inexpensive.

2. Easy to make.

3. Easy to use.

I wanted to maximize all three of these attributes, but most of the spine testers I found maximized two while not maximizing the other. I'm going to show you some other spine testers I found and give my opinion on how they match these criteria.

My YouTube spine tester

Before making the spine tester for this written tutorial, I made an even simpler one for a YouTube video.

Basically, if you have a 2x4 nailed horizontally to the wall, you can build this spine tester in about two minutes. Here's the steps, summarizing the video:

1. Measure out three points on a 2x4 at 0", 13", and 26".

2. Use a square to draw verticle lines at these points across the width of the 2x4.

3. Take a 3/4" thick piece of plywood about 1" x 3", draw a line down the middle, lengthwise.

4. Screw the plywood into the 2x4 at the 13" mark, and line the verticle line on the 2x4 up with the line on the plywood. Make it to where the plywood overlaps the 2x4 by about 1.5", and the other 1.5" sticks up above the 2x4.

At this point, the spine tester is basically done. You just need two more ingredients to use it. Here's how you use it.

5. Put an arrow on the nails.

6. Use a squeeze clamp to clamp a caliper onto the plywood so that it lines up with the 13" line, and the bottom of the caliper barely touches the arrow.

7. Now, put a 2 lbs weight on the arrow as close to the caliper as you can.

8. Now, open the caliper until the little doohickie at the bottom touches the arrow.

9. Read the caliper, and that tells you what the deflection is.

10. Read the spine off an AMO Spine Chart.

The YouTube spine tester was much easier and faster to build than the one I did for the written tutorial because I didn't have to cut any plywood, I didn't use dowels, I didn't put any feet on it, etc. But it works exactly the same.

Inexpensive. The only thing that cost money was the caliper, the hook screw, and the nails. But I already had a caliper because I use it for other things, like bow laminations and bamboo backing. I got the weights for free, so this spine tester almost cost me nothing.

Easy to make. The YouTube spine tester excels in this area. It is probably the easiest spine tester to make that I could think of.

Easy to use. It is not the easiest spine tester to use. It would be easier if I used a digital caliper. The spine testers that use an arm sitting on a pivot that swings up and down are much easier to use than using calipers because you can put the spine weights directly on the scale. You don't even have to look at a chart. And you don't have to adjust a caliper. The micrometer ones are also easier to use.

Sailor's spine tester

Let's talk about the spine tester that inspired mine.

Inexpensive. Most of these materials can be gotten for free, and depending on what you have lying around the house, it might be completely free. Instead of using a squeeze clamp like I did to hold the caliper, he uses a magnet. I had two magnets from radio shack, but they didn't work as well as the squeeze clamp because whenever I tried to operate the caliper, it would move.

Easy to make. His spine tester is not as easy to make as mine. If you've ever tried to get a piece of wood to sit upright on a flat surface without any play, and still get them to be perfectly 26" apart, you'll know it's not easy. Maybe it's my lack of wood working skills, but hammering a nail into a pencil mark is a lot easier. Another option I've considered (and I've seen others do this) is use a couple of shelf brackets. That would make Sailor's spine tester easier to build.

Easy to use. His spine tester is just as easy to use as mine since they both work the same. The only difficulty I had with his method was the magnet and the caliper not staying in place as well as with the squeeze clamp.

The Thin Man spine tester

Thin Man, from the Leatherwall, got the idea for this spinetester from Neilbilly (also from the Leatherwall). I'm using Thin Man's because he's got a better picture, but here is a link to Neilbilly's spine tester.

There's a hole drilled in the shelf at the 13" mark, and that nail just sits on the arrow. When you put the weight on the arrow, the nail slides down. There's a carpenter's square on the shelf next to the nail. To get the deflection, you just find the difference between the initial position of the nail and the final position.

Inexpensive. If you already have a carpenter's square, this one should be dirt cheap. If you don't, the carpenter's square might be costly.

Easy to make. This one is pretty easy to make if you have a shelf you don't mind poking a hole in and as long as you have a drill.

Easy to use. Mechanically, this one is very easy to use. The difficulty is in the fact that you get two different measurements, and you have to subtract one from the other to get your deflection. There is no zeroing this one. That might be somewhat of a pain if you have a lot of arrows to spine.

The Lombard spine tester

This one was made by Lombard from the Leatherwall and can be found here.

Inexpensive. This one is probably less expensive than mine because he doesn't even use a caliper. I'm neglecting the cost of the weight since any weight would do on most of these spine testers.

Easy to make. I question whether the needle is easy to make, but everything else is simple.

Easy to use. This one beats all the others in being easy to use. His scale has the spines written right on it, so you don't even need a chart. And if you scroll down on the thread, he posts a big picture of it, so you can download it and print it for yourself. The only difficulty I see in using this tester is zeroing it out. I'm not sure how he does that.

Stumpkiller's spine tester

This one gets extra kudos from me because of his mechanism for calibrating it. Do you see that little screw on the bottom of the business end of the clothes pin? That's an adjustment screw. You can turn that screw and zero the spine tester before applying the weight. Awesome! See the clothes pin up close on this thread on the Leatherwall.

Inexpensive. This one looks very inexpensive. I can't see anything on it that would be very costly at all.

Easy to make. This one might not be easy to make. I'd like to know how he got that clothes pin mounted without there being a lot of play. It looks like he's got a screw through the spring in the clothes pin to pivot on, but it would have to be a pretty fat screw to avoid play. Maybe it's a bolt. This spine tester has a lot of parts which would add to the difficulty of making this, but the cool factor might make it worth it.

Easy to use. This one appears to be very easy to use. You could use a different scale with just the spine weights on there so you wouldn't have to use a chart.

The Van/TX spine tester

Van/TX from the Leatherwall made this one. It works basically just like the other ones with a swinging arm.

Inexpensive. Dirt cheap. All those materials could be acquired for free at a construction site or on craigslist.

Easy to make. No. Look at the wood working skills that had to have gone into that. I could not have made such a pretty spine tester.

Easy to use. Very easy to use. It looks like he's got an adjustment knob on the right end of the arrow. You turn it to raise and lower the arrow to zero out the tester before adding weight. Cool.

The Stykzz spine tester

I've seen a lot of variations of this spine tester. This one was made by Stykzz on the Leatherwall, but I think Jim Hill came up with the original idea. Here is Jim Hill's spine tester along with lots of pictures and details about how it was made and how it works.

Inexpensive. You can get a micrometer at Harbor Freights for about $10. The bolt and washers might actually cost more than the micrometer. You're going to have to spend money on eye bolts, too.

Easy to make. Not hard, but it's a little more involved than mine.

Easy to use. Very easy to use. Accurate, too. You see, in mine (and in most others) you can't put the weight exactly in the same place as you put the measuring device, but with this spine tester you can.

Here's a much simpler version of the same thing.

This one was posted by a guy on the leatherwall, but I can't remember who or where or I'd give credit and provide a link. When I find it again, I'll do that. Anyway, that's a pvc pipe he filled with lead, BB's, or something for the weight.

The Spine-O-Matic spine tester

2_Smithereenz on Archery talk made this one, though it's not his design. There are more pictures on this thread. For details on how to make it, see this pdf document.

Inexpensive. Quite so!

Easy to make. Nothing with a pointer on a pivot is easy to make in my opinion. At least nowhere near as easy to make as my tester.

Easy to use. Very easy to use. These pointer type spine testers are the easiest to use in my opinion.

The DarkSoul spine tester

I saw this one on a bamboo arrow tutorial on Paleoplanet. There's more detail about it there. Something about the pointing mechanism appeals to me.

Inexpensive. I don't see any parts you couldn't get for free except maybe a screw or a nail. The weight is a brick with a hook screw in it.

Easy to make. Not as easy as mine, but if you like pointers, this one seems easy enough. It might be a trick getting that brick to exactly 2 lbs, but he says he's more concerned about consistency than accuracy.

Easy to use. There doesn't seem to be an easy way to calibrate it in case you use arrows with different diameters or that are slightly warped. Judging by one of the pics on the build along, I'm guessing it may not be as easy to put the arrow on this one as on other's like it.

The CherokeeKC spine tester

CherokeeKC was kind enough to provide a tutorial showing how to build this.

I don't feel like filling out the three criteria anymore. I'm sure by now you can figure that out as easily as I could. It's not as if I made this spine tester.

Design your own pointer system

The first spine tester I made used a protractor and a pointer that was set up basically like this.

I got the idea from a guy on the internet, but I can't find his plans anymore. There used to be a chart that converted the angle of the pointer to spine, assuming 2 inches between the pivot of the pointer and the place where the pointer touched the arrow.

But it's not hard to make your own chart with a little trigonometry.

Remember that Sin θ = opposite/hypotenuse for any right triangle.

And you can see that between the plane of the arrow at rest, and the arrow with a 2 lbs weight on it, there's a right triangle with the pointer providing the hypotenuse and the deflection being the side opposite the angle.

The protractor gives you the angle of deflection, and you know the hypotenuse because you designed it, so just plug in the numbers. You're looking for the "opposite" from the angle θ.

Sin θ = opposite/hypotenuse, so opposite = hypotenuse x Sin θ.

So, from the angle of deflection, you can figure out the deflection of the arrow in inches and use the AMO Spine Chart to figure out the spine weight.

Or better yet, you can make your own chart that takes you directly from the angle of deflection to the spine weight. The AMO Spine Chart gives you the amount of deflection in inches (which is your "opposite" side) and equates it with spine weight. So you can figure out what angle goes with each spine weight by using the chart and solving for θ.

θ = Sin^-1 (opposite/hypotenuse)

Let's do an example. According to the AMO Spine Chart, a 60# spine is equal to 0.433" of deflection. So...

θ = Sin^-1 (0.433"/2") = 12.5 degrees.

So now you know that 12.5 degrees of deflection is equal to 60# of spine weight, assuming 2" between the pivot of your arm and where it touches the arrow.

Or, you could figure out what the spine of your arrow is for each degree of deflection. Let's find out what 15 degrees of deflection gets us.

Sin 15 = opposite/2"

so...

opposite = 2" x Sin 15 = 0.518"

Looking at the AMO Spine Chart, 0.518" of deflection is about 50# of spine weight. So you could make your own chart that equates degrees with spine weight.

Or better yet, you could calculate the spine weight for each degree of deflection, then use your protractor to draw your own scale with the spine weights written right on the scale. That way, you won't even need a chart.

I should tell you that using 1" instead of 2" for the distance between your pivot and where your pointer touches your arrow will give you better precision. And if you don't want to do a lot of calculating, you can cheat with this handy dandy circle with a radius of 1" that will give you the length of the opposite side for every angle as you slide the point around on the circumference of the circle. You can slide it around by putting your mouse on the point, holding down the right button, and dragging it. We didn't have that when I was in school!

Conclusion

There's about a gazillion other spine testers out there. If you want to see more, search google, and search the archery discussion forums, like Tradgang, Paleoplanet, Archerytalk, the Leatherwall, etc. Try "spine tester," "homemade spine tester," "diy spine tester," etc.

Before I go, I wanted to tell you one last thing. The only purpose of having a standardized spine chart is ease of communication. If you were going to making a spine tester with a pointer, you don't even need to use degrees, deflection, spine weight, or any of that. You can simply find the arrow that shoots best from your bow, spine it, and lable your scale with, "My bow." Or you could have a scale with various things like, "My Roy Hall bow," "My Paul Kloster bow," "My favourite recurve," "My favourite longbow," etc. That would make it easier for you to make arrows to match your various bows, though it would not make it easier for you to communicate with other people, like if you wanted somebody to send you arrows or you wanted to send them arrows.

Another thing is that it's more important that all of your arrows be matched in spine and in weight than it is that your arrows be spined correctly for your bow. After all, consistency is essential for accurate shooting, but if your arrows are spined wrong, you can compensate by the way you aim, and as long as they are all wrong in the same way, you can predict where they will shoot.

Upgrade your browser for a better viewing experience »