Author Topic: Are we measuring draw weight wrong?  (Read 243 times)

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Offline Stickhead

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Are we measuring draw weight wrong?
« on: February 14, 2018, 08:11:01 am »
I've often felt that pulling a bowstring by a scale with a small hook isn't really the same as pulling it with three fingers.  If you draw the bow to, say, 26" using three fingers with an arrow in between, then you've got about 2.5" of bowstring at 26".  If you pull the same bow using a scale hook, only about 1/8" of string is at 26".  The rest is at an angle toward the tips, effectively shortening the draw.  Therefore, the actual draw weight using fingers should be slightly higher than that measured with a scale.

I couldn't convince myself on paper whether or not this difference would be negligible, so I did a quick experiment.  I cut a 2.5" piece of PVC to simulate my fingers, and put a bowstring through it.  I then drew the bow to various lengths using: just the scale hook; and using the hook attached to the PVC.  Low and behold, the weight was measurable larger using the PVC.  On this particular bow (which pulls around 60# @ 24"), there was a 1 1/4# difference at 23" (give or take a few ounces due to my imprecise setup). 

I found that if my bow is drawn to 23 1/2" using just the scale hook, it gives the same reading as drawing it to 23" with the simulated fingers.  Therefore, the bow hook underdraws the bow by more than 1/2" when approaching full draw.  This could amount to a 2-3# discrepancy or more, depending on bow length, draw length and bow weight.

Thoughts?

Offline 240m3srt

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Re: Are we measuring draw weight wrong?
« Reply #1 on: February 14, 2018, 08:24:43 am »
Excellent point and insight.  I also wonder about the idea of drawing from a slightly higher point on the string if you shoot split finger.  Perhaps we should be using a 3" pvc to represent 3 fingers, and apply it slightly offset higher than centerpoint of the string when tillering.  I look forward to others response to this.

Offline Badger

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Re: Are we measuring draw weight wrong?
« Reply #2 on: February 14, 2018, 08:30:27 am »
 It is probably somewhere inbetween because the fingers do slope when drawing. I would say about 1/2 of the diff you measured.

Offline PatM

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Re: Are we measuring draw weight wrong?
« Reply #3 on: February 14, 2018, 08:31:53 am »
Hair splitting difference. Your fingers do not maintain a flat hook. The string will be a more open angle with your fingers but not that much.  Many guys use a strap instead of a hook for a better simulation of a true draw.

Offline gfugal

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Re: Are we measuring draw weight wrong?
« Reply #4 on: February 14, 2018, 08:33:52 am »
Nice observation! I still don't know if that's quite enough of a difference to make me want to measure with a PVC though. Also what about thumb draw? that's not three fingers but one.
Greg,
No risk, no gain. Expand the mold and try new things.

Offline Hans H

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Re: Are we measuring draw weight wrong?
« Reply #5 on: February 14, 2018, 08:47:43 am »
Thanks, a intressting idea, I'll try this too.
Hans
Hans,      Bavaria, Germany

Offline Del the cat

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Re: Are we measuring draw weight wrong?
« Reply #6 on: February 14, 2018, 09:03:29 am »
That's one reason why I have a two fingered hook on my scale :)
Del
Health warning, these posts may contain traces of nut.

Offline Pat B

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Re: Are we measuring draw weight wrong?
« Reply #7 on: February 14, 2018, 09:37:48 am »
Draw weight precision only matters if you are selling bows. If it is a few pounds off, who cares as long as you or the intended shooter can comfortably shoot the bow.
Make the most of all that comes and the least of all that goes!    Pat Brennan  Brevard, NC

Offline George Tsoukalas

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Re: Are we measuring draw weight wrong?
« Reply #8 on: February 14, 2018, 10:30:59 am »
Stikhead, I read your post 3 times and did not understand. I'll read it one more time after my nap. :) Jawge
Set Happens!
If you ain't breakin' you ain't makin!

Offline George Tsoukalas

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Re: Are we measuring draw weight wrong?
« Reply #9 on: February 14, 2018, 10:41:31 am »
Never mind. I get it. Going to sleep on it now. :)
Set Happens!
If you ain't breakin' you ain't makin!

Offline Selfbowman

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Re: Are we measuring draw weight wrong?
« Reply #10 on: February 14, 2018, 11:19:44 am »
Draw weight precision only matters if you are selling bows. If it is a few pounds off, who cares as long as you or the intended shooter can comfortably shoot the bow.

I agree Pat. Most bowyers of any custom shop glass or wood bows will tell you up front . I will try my best to hit your weight exactly but I can only be expected to hit plus or minus a pound or two. Some longer bows seem lighter than short bows due to stack. So I have had some guys tell me they could have handled more weight. Most shooters can handle more weight in hunting situations versus target shooting. Any how I agree with Pat.  (W windy Texan
Arvin
Well I'll say!!  Osage is king!!