How to check spine w/o tester

[Over&Under]

This may be a dumb question, but is there any way to check the spine for woodies without a testor and come close?  

Thanks in advance

Jake

[poekoelan]

Some people are good at flexing them and feeling for it, but I wouldn't trust that too much if I was trying to make some real precise arrows.

Do a search here for cheap easy accurate spine tester. For about 10 bucks or so and an hour or so worth of your time, you can make a spine tester that will do as good a job as a store bought one.

Austin

[DarkeGreen]

If you have a good ruler, two post 26" a part and a 2 lb weight you have everything you need. The spine testers just make it a little easier to get good a reading with a long sweeping arm or needle.

[Over&Under]

Darkegreen -

Could you expand a little on the design, and operation?

Thanks alot

Jake

[fingers]

Shoot them without fletching. The arrows that fly true match your bow. The ones that fly to the right (right handed shooter) are weak spined and either need a lighter point or to be shortened depending on how close they are to true flight. The ones that fly to the left are too stiff and need a heavier point if close to true flight. Or they may be poor matches for your bow all together in which case they will really take off to the left or right. Spine testing is about identifying which arrow will fly out of your bow, this method does it in real terms.

[DarkeGreen]

Spine testers do nothing more than measure the deflection of a shaft when a 2 lb weight is set or hung from the center. The 26" distance between shafts is set only to be a "known factor". There are charts on this site, Eastons site, and many others that tell you how much deflection to expect for a given spine. In theory you place the weight on the shaft and measure how much it deflected compare it to the chart. I can't remember off the top of my head but 50# spine is something like .51 or about 1/2".

The problem with this method is being you'll be dealing with very small numbers if you want to be able to tell the difference between, say, a 50# spine and a 52# spined arrow. That's where the arm or needle comes in. Think about a teeter toder. whoever is setting on the short end move the person setting on the long a greater distance. Basically it amplifiies the movement. By doing this you not longer need to be able to read thousands of an inch because the long end of the needle move a greater distance. You will however be able to to tell the differece between a 50# spine and a 60# spine. The smaller measurements you can read on a ruler the more accurate your reading will be.

One could also take the approach of building a device that measured how much weight it took to move a shaft a known distance. The problem with this method is you'd be developing the chart yourself as I haven't found online yet. I think people make this harder than it needs to be. Is really just taking measurements of movements.

I've seen one spine tester posted on here that used a slot in a board with a wrench hanging from one end. He used know spined shafts and then marked a line on a board behind it. Now when you place a unknown shaft on the board you just check to see which line on the board it matches and read the number you wrote for whatever spine it was.

Did that help or did I muddy things up?

[Over&Under]

That helped a ton! The part I didn't know was how the amount of deflection correspoonded to spine, 1/2 = spine? 3/4 = spine? and so forth, but since there is a chart, that answers that question.  So I could suspend a shaft across two objects that are 26" apart, put a straight edge across them as well, assuming it is level, and the measure from the bottom of the straight edge to the bottom of the arrow, take that measurement and put it against the chart and see what happens.  Am I right so far?  The the more accurate the measurement the more accurate the spine?  how did I do?

Thanks alot for your help...

Jake

[Dr. Ed Ashby]

Jake,

Crude, fast and not absolutely precise, but here's how I used years ago to sort masses of dowel rods. It works very well.

Mount a 2x4 on the edge of you work bench (or a wall will work). Drill a hole of the correct size to accept whatever diameter shaft your sorting.

Now, take a shaft that you know is the right spine for your bow (and you can do this for several different spines, for several bows, if need be). Insert it into the hole.

Next, take any suitable weight, the exact amount isn't too critical. Suspend the weight on the end of the shaft opposite the block.

The shaft bends. Now place a mark on your work bench (or the wall) to mark where the very end of the bent dowel is positioned - i.e.; mark how much the shaft has bent.

All you have to do is insert each shaft and repeat the process. Shafts of the 'right spine' will bend exactly to the mark. Those too stuff will bend less, and those too weak will bend too much.

If trying to sort shaft for several bows, just label each reference point that you've made on the work bench or wall.

Cheap, fast, and gives a closer result than most would believe!

Ed

[Over&Under]

Dr. -

Thanks to you as well for that alternate simple option.  I need to find out the spine of a single arow in order to test the rest.  

Thanks to all

[StanM]

I'll take pics of mine in the morning.  It's pretty simple.

Stan

[poekoelan]

The design I mentioned is essentially the same thing, only it uses a protractor instead of a ruler. The protractor can measure deflection more precisely. Hang a two pound weight on 26" centers and measure with a protractor. That's basically it.

[Dr. Ed Ashby]

Jake, the very best method of finding the spine that's correct is for YOU and YOUR bow is to bare shaft it. That gives you the dynamic spine, rather than the static spine. It will shoot right for YOU from THAT individual bow. Then use shafts with a static spine the same as the one that shoots correctly. It'sd that simple.

Ed

[StanM]

Jake,

I took a pic of my spine tester and put it in the thread "Arrow build-a-long".

Stan

[Over&Under]

Man it pays to ask question around here!  Thanks guys for all the input! It is much appreciated!

Now off to the shed for some testing...