Measuring draw weight

[RoyseCity]

I have a digital scale, but I'm not sure if I am using it correctly.

I hang it using a nylon strap. It stretches as I apply weight.

My question is, does that stretch affect the accuracy of the measurement?

Or does it all come out the same?

Should I hang it from something solid (like a steel hook) in order to get an accurate measurement?

Joe

[little john]

In my opinion the stretches negligible we are only going to be one to two pounds off

[LAW]

solid

[RoyseCity]

You're probably right, John.

Still, I want to know if it affects measurement at all.

A man who understands physics and engineering could likely answer definititively.

Joe

[hot_rod_eddie]

Traditional makes no difference, but a compound will be slight affected.

[DEG]

Stretch will not cause any weight loss to the scale. if it takes 2 lbs or 60 lbs to stretch the strap, it will all be registered on the scale provided the scale is between the strap and the bow.

[hot_rod_eddie]

It would take me back to my differential calculus days to determine the difference, but I can assure you that a stretchy material like nylon (rubber band in the perfectly plastic area of the stress/strain curve) will make a difference on a compound bow that is also going through a non-linear curve. You have two systems deforming at different rates over a point of a cam profile and it will make some difference. Now if you just wanted to know the let-off poundage of the compound, it wouldn't be a problem because you would be in steady state. The same when using a traditional bow.

[SwampRabbit]

Since we are measuring static hold weight, the stretch in what is holding the scale does not matter. All the stretch can induce is a little slop in trying to maintain the static hold position for an accurate reading. But as long as everything is static, the scale will measure the force being applied through it.

[hot_rod_eddie]

Since we are measuring static hold weight, the stretch in what is holding the scale does not matter. All the stretch can induce is a little slop in trying to maintain the static hold position for an accurate reading. But as long as everything is static, the scale will measure the force being applied through it.

SR - for a compound you are not measuring the static weight, you measure the maximum weight as you come over the cam nose.

[SwampRabbit]

SR - for a compound you are not measuring the static weight, you measure the maximum weight as you come over the cam nose.

Joe is shooting a traditional bow and posted the question on the trad forum

But eddie, even with a compound bow, you are measuring the total force that goes through the point. Even if you have stretch it won't matter in finding peak, because the peak force is seen only once during the draw cycle. Having stretch makes it harder on the guy pulling on the bow to get a feel for when to let go because there is more recoil when it breaks and the stretch pulls back up and the person applying the force continues to apply force.

[DEG]

Help me understand this Hot Rod. Based on your answer. If I use a release with a nylon strap between my wrist strap and the release I will not be pulling what my bow is set at? Not trying to be a smart a** just trying to understand.

[SwampRabbit]

I think what you are trying to describe is the fact that finding peak on a compound requires you to sweep the draw curve. The only way to do this properly is to sweep the draw slowly and note the peak. Once you hit the letoff point the recoil in the mechanics of the scale can present problems, as can when you hit the wall and you keep increasing pressure beyond the peak. Doing this manually, by hand can give you a good idea, but in reality, you need to measure at static points to find the peak.

And there is a difference between stretch and spring. Stretching a strap doesn't store up any energy. Springs store energy and can cause oscillation which can throw you off when slowly sweeping.

[hot_rod_eddie]

Joe is shooting a traditional bow and posted the question on the trad forum

But eddie, even with a compound bow, you are measuring the total force that goes through the point. Even if you have stretch it won't matter in finding peak, because the peak force is seen only once during the draw cycle. Having stretch makes it harder on the guy pulling on the bow to get a feel for when to let go because there is more recoil when it breaks and the stretch pulls back up and the person applying the force continues to apply force.

Sorry about that. I was just checking 'new posts'.

[SwampRabbit]

Sorry about that. I was just checking 'new posts'.

No need to apologize... was just clearing up why he was getting the answers he was from the rest of us. But even with trying to find the peak on a compound, stretch is fine, assuming you are following the proper technique for finding true peak and not just trying to eyeball it.

[hot_rod_eddie]

Help me understand this Hot Rod. Based on your answer. If I use a release with a nylon strap between my wrist strap and the release I will not be pulling what my bow is set at? Not trying to be a smart a** just trying to understand.

The difference will be ridiculously small, but the OP asked if there would be any difference. From an engineering standpoint yes, but probably about 3 decimal places back. Sorry to blow up the trad thread.