bigcountry

Got a bowscale for Christmas. And was measuring my bows. Got me thinking. A bow set at 70lbs, you should deduct the bow's wieght because every bow is different. So I put my bowscale on the ground and pulled up and sure enough, I was ~4lbs less weight. Makes sense.

Question is, does any proshop take bow wieght into account? Or zero out thier scale before weighting? I have never seen any proshop take it into account. Just thinking.

Arthur P

Now that you mention it,I've never seen it taken into account at a shop either.

A friend of mine has a rig where the scale is on a rope over a pulley. The bow is locked in place in the fixture, scale hooked onto the stringand then the rope is pulled. There is a yardstick on the back board that lets you check poundage at different draw lengths. I just assumed a variance between scales when the bow checked different on the shop scale than it does on his.

It's too early in the morning to figure this'n out. [8D]

Sylvan

Actually, if you're trying to measure the amount of force necessary to draw the bow then you wouldn't subtract the bow's weight. Now of course this assumesthe typical condition that the scale is attached to the string not the bow, i.e. the scale is above, you place the string on the scales hook and then pull down on the handle. If you place the bow handle on the scales hook and then pull down on the string then you would subtract the bows weight. I wouldn't recomend doing it that way though.

In the typical measurement condition, if you subtract the weight of the bow, the result would be only the amount of force you are applying with your hand to pull the bow down. The total force to draw the string would include the bow weight which is also helping to draw the string and that of course is precisely what the scale reads.

bigcountry

Nope sylvan, because if you put your scale on the floor and pull up, its 4lbs off at peak wieght compared to the ceiling. Or if you put it on the wall and pull horizontially, you havemostly ahorizontial vector, and a slight vertical vector of force. Still peak weight is about 3lbs off of max peak wieght from hanging on the ceiling. Where the floor test is 4lbs.

Put the bow on the bow scale hanging on the ceiling and do not put any force on it. Your wieghing the bows wieght.

I don't know, you may be right. Because if the bow theoretically wieghted 70lbs and you hung it on teh scale itself, it would pull the bow down and peak out at 70lbs. Some reason I am having a hard time understanding this.

Sylvan

bc,

Think of it this way... When you hang the bow string on a scale, the weight of the bow actually starts the draw. It won't be much but if the bow weights 5# then it will be some. Now imagine hanging a 40# weight on the bow. Now you will have a total of 40# + 5# = 45# pull onthe string and you will clearly see that the bow is now drawn several inches. Your scale would read 45# also. Its reading the weight of the bow plus the additional weight you've added. Nowif you put your hand on the handle and push down to bring the measurement to peak weight (lets assume peak is 70#) you would only need to push down a little bit. Theoretically 25# because 40+5+25=70. Themore weight you hang on the bow, the less you push with your hand to get to peak.

Like I said earlier. Given a typical measurement condition, if you subtract out the weight of the bow the result is the force you exert on the handle but that's not what you're after. You want to know the force to draw the string.

I'm not sure why you're getting a difference when you pull up fro the floor. Is the scale upside down relative to gravity, you put the string on the scales hook and pull up on the bow handle? Off the top of my head the only thing I can think of is maybe there is some slop in the scale that is taken out when it is right side up but not upside down. Not sure but it shouldn't matter what direction you pull. The scale only measure the force applied to it and that is independent of direction. If you attach the string to the fixed scale and pull the bow away or you fix the bow in place and pull the scale away the scale sees only the force between the string and itself.

ranger56528

When you start pulling down on the bow it dosnt matter because your force is takeing over untill it cams over,thus the weight of the bow makes no differance.....If your bow weighs 3.8#'s,as soon as you hang it on the hook you are apling 3.8# of draw weight on the stringand then force takes over untill you cam it over......Scale should be at zero with no bow.........


EDIT......No EDit

bigcountry

I understand. All the scale is doing is measuring upwards force. Thanks guys.

TFOX

I agree with sylvan and ranger,the bow's weight is irrelevant.It only assist the force needed to draw it.

nodog

I think you said it best.

If you put a 70 pound weight on the bow you wouldn't have to pull it at all, it would justpull on it's own.