Archery Talk Forum banner

1 - 20 of 20 Posts

·
Registered
Joined
·
336 Posts
Discussion Starter #1
Comments & Questions on building and using these types of spine testers:
Dial indicators have an internal spring which pushes the plunger completely out, when the indicator is resting "free".

Depending on the make & model and range of the indicator, this internal spring can develop a fair amount of counter-force, which pushes in the opposite direction of the carefully calibrated 2 pound weight.

For arrows spined in the low weights (example: an arrow spined for 30 pounds has a deflexion of 0.867 inches), this counter-force can completely skew your results. As a spring becomes more compressed, it pushes back with increasing force.

My dial indicator can develop 5 ounces of force over it's full range of 0 to 1.050 inches. That's about a third of a pound! This is a significant opposite force against the 2 pound weight!

Soooo....anybody have any ideas, experience, insights on dealing with this anomaly? Sorry for the long post, sometimes I gotta build the bridge as I cross it. Mebbe it's time fer one of these:cocktail:

Good Loosing!
 

·
Registered
Joined
·
15,839 Posts
In general, any type of measurement can be improved with the quality of the equipment. Therefore, you probably want to use a real good instrument if you want accurate results.

However, for my purposes, if I had a spine tester, it would be to obtain uniform results. So, in this case, if the instrument is basically repeatable then that is really all I would be concerned with.
 

·
Simon Cowel of AT
Joined
·
6,595 Posts
Deezlin said:
In general, any type of measurement can be improved with the quality of the equipment. Therefore, you probably want to use a real good instrument if you want accurate results.

However, for my purposes, if I had a spine tester, it would be to obtain uniform results. So, in this case, if the instrument is basically repeatable then that is really all I would be concerned with.
There we have the best answer I could think of... I have a Easton tester and without going to crazy money with lasers I bet the dial will provide the info any archer would need..... A manufacturer is another story... But I bet they have that issue fixed by the time they have arrows to test ;)

If you want to buy a Easton Spine Tester give me a PM.... I may just be coaxed into parting with mine....:wink:
 

·
Registered
Joined
·
4,058 Posts
Good points all, and unless you were to go to a deflection pointer instead of a dial indicator, you have very little choice other than lazers.

At least with a deflection pointer, you can calibrate your marks, but than again, just how important is it to get the exact deflection?

Most of us use spine checkers to verify uniformity, not exact spine.
 

·
Registered
Joined
·
149 Posts
Deflection

When I designed the Carbon QC ( www.ram-products.com ) I was concerned about the deflection induced by the spring. This turned out not to be a problem because the spring pressure has a very slight change in the small amount of travel when the arrow deflects because of the 2 pound weight. If you set the zero on the dial indicator with no wieght, then add the weight, the error caused by the indicators spring is only the amount that the spring load has changed because of the travel. In other words, the spring load is for all intents and purposes the neglible at 0" as it is at -.340". This is even less of a problem since the spring constant will remain the same through out the life of the indicator... thus, it will be the same amount of error (<.001") for every arrow tested.
 

·
Registered
Joined
·
123 Posts
On my indicator it was a very simple task to just remove the spring and let gravity alone do the job. Works great.
 

·
Registered
Joined
·
815 Posts
Wooly....

When I built my own spine tester early last year, the main objective was to check the consistency of each arrow compared to the next - relative indication of spine and the location of the high side. I was not too worried about actual deflection.

However, I did take into consideration what you have said about the sping force. Before I made my test weight, I measured the weight required to compress the spring in the dial indicator. I then added that amount of weight to my test weight.

Does it really make a difference? I don't know, but I do know that I feel better about what I did and if I really want to measure true deflection, I don't need to worry about it.
 

·
Registered
Joined
·
336 Posts
Discussion Starter #8
Using dial indicator spine tester

Thanks everyone for your responses. In general, most dial indicators have an internal spring which exerts some force, and this force increases the further one depresses the plunger.

Looking at an arrow spine chart: the difference between a 30 pound spine and say, a 50 pound spine, is 0.347 inches. That's actually not much, and therein lies the problem!

If you test an arrow with this style of tester, leave the two pound weight in place, and watch the arrow shaft move downwards as you carefully remove the dial indicator. It will move down...how much? Depends on the individual dial indicator and it's full range capability, and the shaft you are testing!

There's an old maxim that states most things being tested are influenced by the tester...and Archersteve nails it dead-on. Just use the tester to find uniformity amongst the shafts. I'm talking wood arrows here.

Do pointer-type spine testers have a method to compensate for any false load put on the arrow shaft? And, just how close in spine does one have to get with respect to the spine charts? And, how did they determine such exactness? Did someone develop bow shooting machines?

Buggers...I do not want to take the fun out of arrow-building nor hunting. I am truly puzzled as to how this all evolved. Like a fart in a phone-box, it shan't dissappear so quick. Yaaarrrrgh! :darkbeer:
 

·
Bow Bender
Joined
·
6,302 Posts
WoolyWelsh said:
Thanks everyone for your responses. In general, most dial indicators have an internal spring which exerts some force, and this force increases the further one depresses the plunger.

Looking at an arrow spine chart: the difference between a 30 pound spine and say, a 50 pound spine, is 0.347 inches. That's actually not much, and therein lies the problem!

If you test an arrow with this style of tester, leave the two pound weight in place, and watch the arrow shaft move downwards as you carefully remove the dial indicator. It will move down...how much? Depends on the individual dial indicator and it's full range capability, and the shaft you are testing!

There's an old maxim that states most things being tested are influenced by the tester...and Archersteve nails it dead-on. Just use the tester to find uniformity amongst the shafts. I'm talking wood arrows here.

Do pointer-type spine testers have a method to compensate for any false load put on the arrow shaft? And, just how close in spine does one have to get with respect to the spine charts? And, how did they determine such exactness? Did someone develop bow shooting machines?

Buggers...I do not want to take the fun out of arrow-building nor hunting. I am truly puzzled as to how this all evolved. Like a fart in a phone-box, it shan't dissappear so quick. Yaaarrrrgh! :darkbeer:
I showed my RAM testor to my machinist buddy who is really, really good by the way, and he liked everything about it except the pressure the dial indicator put on the shaft. He thought that the run out on the indicator should be less. In other words, if we raised the whole dial up so that the amount of pressure from the spring is less, then the machine would be more accurate.

He also noted to really see how straight a shaft was or get better readings he thought that you should place the same dial indicator setup on either end of the shaft as well as in the middle and that would give you quite a bit more information.

I'm new to all this, but it makes sense to me. I am going to build a taller braket for my machine and do three of them so I can get "lighter" spring pressure and see what is happening on either end of the shaft.

Or I could just shut up and go shoot.....:wink:
 
S

·
Guest
Joined
·
0 Posts
I have had the opertunity to test both a dial and laser indicators when I was testing the comparitive spines on the Cartel arrows to Easton spects, what was interesting was that the dial and laser were exact up to 3 decimal places and since spines are only listed up to 3 decimals places the difference was negliable certainly nothing to worry about, what was neet was to see the laser pick up on the shaft coatings ie carbon vs aluminum
 

·
WapitiBob
Joined
·
6,935 Posts
The problem with taking advise from a machinist buddy is that most of us think we know what we're talking about.:pukey:
If you zero the indicator then add the weight, the deflection imparted on the arrow by the indicator isn't enough to worry about, and besides, the indicator is
ZERO'd out with the weight of the pin taken into account, THEN you add the weight and read the deflection. No differrent than if the arrow was bent a cpl thou.

You're not looking to see how straight the arrow is when measuring deflection (spine) of the arrow as you never spin it without re zeroing the indicator.
 

·
Bow Bender
Joined
·
6,302 Posts
Bob_Looney said:
The problem with taking advise from a machinist buddy is that most of us think we know what we're talking about.:pukey:
If you zero the indicator then add the weight, the deflection imparted on the arrow by the indicator isn't enough to worry about, and besides, the indicator is
ZERO'd out with the weight of the pin taken into account, THEN you add the weight and read the deflection. No differrent than if the arrow was bent a cpl thou.

You're not looking to see how straight the arrow is when measuring deflection (spine) of the arrow as you never spin it without re zeroing the indicator.
Okay, I got a question for you. And this is serious, not some sort of challenge. I ordered 35 dozen arrows that I want to sort by spine and straightness. I got what I thought was a few straight arrows, maybe 45 or so. Now I put these on the Ram machine per the intructions to test the spine. I started sorting them according to what I was reading on the dial. Then I did something that made me wonder. I rotated a shaft and got a difference of .006 on the spine, just by rotating the shaft under a load. Now I had 25 of these other shafts sorted my deflection. I took them and put them back on the machine, and started getting readings all over the place. So that being the case, how do you know where to measure the spine on any given shaft? I could get 5 different readings from the same shaft, entirely depending on the shaft orientation when it was placed on the machine. How do I overcome this problem? :confused:
 

·
Registered
Joined
·
19,164 Posts
Super 91 said:
Okay, I got a question for you. And this is serious, not some sort of challenge. I ordered 35 dozen arrows that I want to sort by spine and straightness. I got what I thought was a few straight arrows, maybe 45 or so. Now I put these on the Ram machine per the intructions to test the spine. I started sorting them according to what I was reading on the dial. Then I did something that made me wonder. I rotated a shaft and got a difference of .006 on the spine, just by rotating the shaft under a load. Now I had 25 of these other shafts sorted my deflection. I took them and put them back on the machine, and started getting readings all over the place. So that being the case, how do you know where to measure the spine on any given shaft? I could get 5 different readings from the same shaft, entirely depending on the shaft orientation when it was placed on the machine. How do I overcome this problem? :confused:
http://webstore.ansi.org/ansidocstore/product.asp?sku=ASTM+F2031-05

Above is a link to the standard for testing arrow spine... The spine is tested at 4 locations equally spaced 90 degrees apart... and the average is the arrows rated spine. That of course isn't the entire proceedure... download and read...
 

·
WapitiBob
Joined
·
6,935 Posts
"I could get 5 different readings from the same shaft, entirely depending on the shaft orientation when it was placed on the machine. How do I overcome this problem?"

And now you know why people tune the nock orientation on the arrow. Either the Javi paper plate method or with a hooter shooter. :wink:
 

·
Bow Bender
Joined
·
6,302 Posts
Bob_Looney said:
"I could get 5 different readings from the same shaft, entirely depending on the shaft orientation when it was placed on the machine. How do I overcome this problem?"

And now you know why people tune the nock orientation on the arrow. Either the Javi paper plate method or with a hooter shooter. :wink:
I have done that in the past by just shooting and rotating the nocks till I got the best arrow flight. But this year I am working hard to try to get it done so my fletching orientation and my nock rotation are the same using the RAM tool. But some of the readings seems to be up in the air a bit to me. I will look at Javi's site and see what I can learn. Thanks
 

·
Bow Bender
Joined
·
6,302 Posts
JAVI said:
http://webstore.ansi.org/ansidocstore/product.asp?sku=ASTM+F2031-05

Above is a link to the standard for testing arrow spine... The spine is tested at 4 locations equally spaced 90 degrees apart... and the average is the arrows rated spine. That of course isn't the entire proceedure... download and read...
I guess I need to pay the $29.00 to download this document. Not exactly what I was thinking.....:sad:
 

·
Registered
Joined
·
19,164 Posts
Well that is the published standard for testing, and I have nothing to do with the copyright laws. That isn’t my site and although I have paid the $29.00 under the law I can’t distribute it. So yes, if you want to know exactly how to perform the tests then you will have to spend the money just as I did…
 

·
Bow Bender
Joined
·
6,302 Posts
Okay. I just thought it was a free site for some reason. If it is worth the $29.00, then that is a small price to pay for good info.
 

·
The Rut Rascal
Joined
·
1,744 Posts
ASTM F2031-05(2010)


Standard Test Method for Measurement of Arrow Shaft Static Spine (Stiffness)
1.1 This test method covers the formulation and designation of arrow spine measurement standards and nomenclature for arrow shafts.

1.2 The English system of measurement, specifically inches of deflection, shall be used for all spine values expressed for a given arrow shaft.

1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

NOW $35.00
 

·
Registered
Joined
·
7,265 Posts
When I built my spine tester I also intended to use it to check straightness. As long as you have the internal spring in the indicator you can't tell whether you're actually measuring run-out or spine variations.

Indicators are made to function in any orientation and the spring is much heavier than it needs to be if the indicator only needs to function in the vertical (mounted above the shaft) position. I've found that the higher end models sometimes are constructed such that the spring is easily removed and the function is not affected. The low end models typically use a cheaper method of manufacture and removing the spring can be a real pain or impossible. At least with my skill level! Luckily for me, as a machinist of over 40 years, I've collected numerous indicators and had one that was easily modified.

I do agree if you're only interested in relative stiffness the above methods will work well, but I would never rely on a strong spring checking straighteness.

I built mine back when I was shooting wooden shafts and really wanted an absolute value that was accurate.

Best of luck to you.
 
1 - 20 of 20 Posts
Top