Puzzled by draw length/weight markings
01-12-2002, 12:05 PM
#1
Spike
Thread Starter
Join Date: Feb 2003
Location: Centennial CO USA
Posts: 29
Puzzled by draw length/weight markings
I've searched all the posts, and there is a lot of info out there. My question is, if you have a bow marked 50#@28", made by a reputable bowyer, but not marked "AMO", where would you expect the 28" mark measured from the string/arrow nock to be when there is 50# of pull applied? Even with the dished part of the grip? Even with the farthest away portion of the riser - called 'the back' even though it's the front when you're shooting??? Even with the contact point on the shelf? I've been measuring mine and it's really got me puzzled. 50 lbs. pull gives me 30.25 inches for the shortest possible arrow with no broadhead clearance. I'm wondering if this bow is a little lighter than marked. What kind of variation is there amongst bowyers - it sounds like lots.
Thanks! Tom
Thanks! Tom
01-12-2002, 03:46 PM
#3
Join Date: Feb 2003
Location: West Bloomfield Michigan USA
Posts: 262
RE: Puzzled by draw length/weight markings
The AMO spec calls for measuring the draw weight at 26 1/4" from the string to the pivot point of the riser. Then they add 1.75" to that for broadhead clearance and state the bow's # at 28" Thus a 50#@28" bow is really 50# when the string is drawn back 26.25" from the pivot point on the riser, which may be the deepest portion of a dished grip or it may not, depending on how the arrow shelf is constructed in relation to the grip. (Have I confused you all enuf now?)
But since Tom's bow does not have an AMO indication on it, the bowyer might have measured the weight at 28" from the back of the bow (side facing away from the archer) or the belly of the bow (side facing the archer) or some other arbitrary point in between --- no way of telling. Since a 30.25" draw is required to achieve 50# of draw weight, my guess is the bowyer measured the weight at 28" from the belly of the riser, which means the bow is just slightly underweight when measured using the AMO standard.
Jack
But since Tom's bow does not have an AMO indication on it, the bowyer might have measured the weight at 28" from the back of the bow (side facing away from the archer) or the belly of the bow (side facing the archer) or some other arbitrary point in between --- no way of telling. Since a 30.25" draw is required to achieve 50# of draw weight, my guess is the bowyer measured the weight at 28" from the belly of the riser, which means the bow is just slightly underweight when measured using the AMO standard.
Jack
01-12-2002, 05:29 PM
#4
Spike
Thread Starter
Join Date: Feb 2003
Location: Centennial CO USA
Posts: 29
RE: Puzzled by draw length/weight markings
Thanks PB and Floxter..
I'm still working on it. 50 lbs. pulls the 28" mark 9/16" out in the air on the belly side of the riser. 46 lbs pulls the 28" mark to the dip of the handle locator grip, close to the mystical pivot point (I'm not sure what that is either!) I'm using weights that have been checked out, not a spring scale. All I know is I have a bow that does not pull close to 50 lbs when a 29" arrow is drawn to the base of the point. It looks to me like it's off about 4 lbs., and that's too much for a 50 lb. bow. I'm gonna recheck the weights I'm using, just to make sure.
Now let me see....IF I have this right, then length for weight marking is not draw length, and neither one is the same as arrow length, and if you're shooting cedars you need 'em spined to your bow, but they ought to be an inch or so longer than your draw length to the back(away from archer) side of the riser, and if that makes them longer than 28" (even though the spine deflection is measured at 26"!) -- they will act weaker, so you need more spine. The only way to know how much poundage is being applied to your arrow is to put your bow on a good scale and check it at the length you pull it. Then you have a starting point for selecting shafts, etc. If I was ordering a custom bow today, I'd just tell the bowyer that I want a bow that pulls xxx lbs. when the string is xxxx inches from deepest part of the grip. That's the only measurement that the archer has control of. Then the bowyer can put as much lumber as he wants forward of that point. This is fun!
Tom
I'm still working on it. 50 lbs. pulls the 28" mark 9/16" out in the air on the belly side of the riser. 46 lbs pulls the 28" mark to the dip of the handle locator grip, close to the mystical pivot point (I'm not sure what that is either!) I'm using weights that have been checked out, not a spring scale. All I know is I have a bow that does not pull close to 50 lbs when a 29" arrow is drawn to the base of the point. It looks to me like it's off about 4 lbs., and that's too much for a 50 lb. bow. I'm gonna recheck the weights I'm using, just to make sure.
Now let me see....IF I have this right, then length for weight marking is not draw length, and neither one is the same as arrow length, and if you're shooting cedars you need 'em spined to your bow, but they ought to be an inch or so longer than your draw length to the back(away from archer) side of the riser, and if that makes them longer than 28" (even though the spine deflection is measured at 26"!) -- they will act weaker, so you need more spine. The only way to know how much poundage is being applied to your arrow is to put your bow on a good scale and check it at the length you pull it. Then you have a starting point for selecting shafts, etc. If I was ordering a custom bow today, I'd just tell the bowyer that I want a bow that pulls xxx lbs. when the string is xxxx inches from deepest part of the grip. That's the only measurement that the archer has control of. Then the bowyer can put as much lumber as he wants forward of that point. This is fun!
Tom
