Primitive Archer
Main Discussion Area => Bows => Topic started by: Don Case on August 06, 2013, 03:09:53 pm
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Is draw weight linear? If I have a bow that is 10# at 12" draw will it be 20# at 24" draw?
Thanks
Don
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2-3# per inch is normal. 10# @ 12" would be darn close to 40# @ 24".
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2-3# per inch is normal. 10# @ 12" would be darn close to 40# @ 24".
So what about a bow that pulls say 27 pounds at 28 inchs ?
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Its a spongey piece of junk.
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Google search for "traditional bow fd curve images" and take a look. Within the working range of the bow, it is relatively linear - but not 1:1 as in your example. However, there is a point when the bow begins to "stack" - where the angle of the string is > 90 degrees at the nocks and therefore you begin pulling more force along length of the limb rather then bending it. At this point the FD curve becomes asymptotic.
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Thanks, that's what I was looking for.
Don
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Damn pearl, that actually made me laugh outloud :laugh:
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I find heavier bows (above 60-70#) usually gain 5# per inch. Below that, the usual normal is about 3# per inch.
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Its a spongey piece of junk.
:laugh: :laugh: :laugh: :laugh: ROFlOl!
Been there done that. Got one hanging over my wood stove right now....Gonna use it to start a fire this fall.
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Its a spongey piece of junk.
Sure but the 2-3 pound is more of an average not every bow is the same 2-3 pounds an inch
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Its a spongey piece of junk.
Sure but the 2-3 pound is more of an average not every bow is the same 2-3 pounds an inch
I have only made 12 bows so far and as an average it is 2-3 lbs per inch. If it's less than that or more something is wrong with tiller/design. towards the end of draw length/weight it may gain like 3.5 lbs per inch on the last inch. This is also called stack. how much a bow gains poundage depends on how much wood there is and where it is at on the limb as well as lenght of bow and lenght of draw. Lots of variables here to account for. Generally speaking ya want 2-3 lbs per inch.
Hope this limited knowledge helps.
Greg
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Its a spongey piece of junk.
Sure but the 2-3 pound is more of an average not every bow is the same 2-3 pounds an inch
I have only made 12 bows so far and as an average it is 2-3 lbs per inch. If it's less than that or more something is wrong with tiller/design. towards the end of draw length/weight it may gain like 3.5 lbs per inch on the last inch. This is also called stack. how much a bow gains poundage depends on how much wood there is and where it is at on the limb as well as lenght of bow and lenght of draw. Lots of variables here to account for. Generally speaking ya want 2-3 lbs per inch.
Hope this limited knowledge helps.
Greg
I really don't want to argue about it but I disagree your saying tht a 120 pound warbow is still only gonna pull 2-3 pounds an inch ? And that a 20 pound bow is gonna pull 2-3 pounds an inch ? I don't think so. And saying that if it doesn't pull 2-3 pounds per inch then it is the wrong design/tiller is just silly
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Didn't we just have this discussion a couple of months ago? ....................................At brace height(6" for ex.)it's 0 lbs. The gain will depend on final draw weight and length drawn.
60#@ 28" means you are pulling 60lbs over a 22" distance (28"-6" brace) Therefore 2.7272 lbs per inch
120 #@32" means you are pulling 120lbs over a power stroke of 26" Therefore 4.6153 lbs per inch
For practical purposes (hunting bows of 45 -65lbs) we are talking 2-3 lbs./ inch .
If you were to get a dramatic increase in draw near it's limit, it's a design flaw (stacking)
Disclaimer :The discussion may have been on another site
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Yup... we just hashed this out about a month ago.
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Just use some common sense guys. It depends on a few things but non of them rocket science ;)
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What Mike said, all I want it for it to gain weight pretty even as you draw inch by inch,then it will be a smooth bow,obviously the heaver you want the bow to wind up the more per inch it will gain,most bow I make are in the low 50's and gain
2 to 3 lbs per inch. :) EST. :)
Pappy
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I had a feeling I should have put 5-6 disclaimers in there to cover ALL the bases rather than just 92.421% of them.
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;) :) :)
Pappy
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They tend to be pretty linear and it's easy to do the arithmetic...
BUT The thing you have to remember is draw length isn't draw length!!! :o
10" 'draw' is really 10" minus the brace height. So your 10# at 10 " isn't 1# per inch increase it's really 2# per inch!
This blog entry may be of interest! It explains why a lady shooting a little 35# Hazel bow was shooting as far as some guys with a 50# longbow!
http://bowyersdiary.blogspot.co.uk/2013/07/draw-and-poundage-arithmetic.html (http://bowyersdiary.blogspot.co.uk/2013/07/draw-and-poundage-arithmetic.html)
But even this is a simplification.
You really want two figures say at 10" and 20" draw you can then subtract the lengths from each other. Subtract the poundages from eachother divide the poundage by the distance and get a reasonable figure.
E.G 15#@10" and 35# @20" would give (35-15)# over (20-10)" which is 20/10 which is 2# per inch
Del
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Its a spongey piece of junk.
Sure but the 2-3 pound is more of an average not every bow is the same 2-3 pounds an inch
I have only made 12 bows so far and as an average it is 2-3 lbs per inch. If it's less than that or more something is wrong with tiller/design. towards the end of draw length/weight it may gain like 3.5 lbs per inch on the last inch. This is also called stack. how much a bow gains poundage depends on how much wood there is and where it is at on the limb as well as lenght of bow and lenght of draw. Lots of variables here to account for. Generally speaking ya want 2-3 lbs per inch.
Hope this limited knowledge helps.
Greg
I really don't want to argue about it but I disagree your saying tht a 120 pound warbow is still only gonna pull 2-3 pounds an inch ? And that a 20 pound bow is gonna pull 2-3 pounds an inch ? I don't think so. And saying that if it doesn't pull 2-3 pounds per inch then it is the wrong design/tiller is just silly
Got the proof setting in my corner of shop. Tiller one really screwy and pull it to full draw you will see what I mean. Leave the inner limbs way to stiff and see what happens ;) It will stack bad and gain more than 3 lbs per inch the last 4 or 5 inches. 3.5 lbs per inch over 30 inches = 105 lbs so its ABOUT 3 lbs per inch. No one claimed to have some formula set in stone. If its a 400 lb cross bow of course it's not going to be 2 lbs per inch.
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I think Del has it right ,but all this math is making my head hurt!
Think I will just go make a bow , it is more relaxing and way more fun than all this math !
Have fun !
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Its a spongey piece of junk.
Sure but the 2-3 pound is more of an average not every bow is the same 2-3 pounds an inch
I have only made 12 bows so far and as an average it is 2-3 lbs per inch. If it's less than that or more something is wrong with tiller/design. towards the end of draw length/weight it may gain like 3.5 lbs per inch on the last inch. This is also called stack. how much a bow gains poundage depends on how much wood there is and where it is at on the limb as well as lenght of bow and lenght of draw. Lots of variables here to account for. Generally speaking ya want 2-3 lbs per inch.
Hope this limited knowledge helps.
Greg
I really don't want to argue about it but I disagree your saying tht a 120 pound warbow is still only gonna pull 2-3 pounds an inch ? And that a 20 pound bow is gonna pull 2-3 pounds an inch ? I don't think so. And saying that if it doesn't pull 2-3 pounds per inch then it is the wrong design/tiller is just silly
Got the proof setting in my corner of shop. Tiller one really screwy and pull it to full draw you will see what I mean. Leave the inner limbs way to stiff and see what happens ;) It will stack bad and gain more than 3 lbs per inch the last 4 or 5 inches. 3.5 lbs per inch over 30 inches = 105 lbs so its ABOUT 3 lbs per inch. No one claimed to have some formula set in stone. If its a 400 lb cross bow of course it's not going to be 2 lbs per inch.
Yep
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I think Del has it right ,but all this math is making my head hurt!
Think I will just go make a bow , it is more relaxing and way more fun than all this math !
Have fun !
Yep ;) gotta try to patch some frets on a hickory bow.
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Damn pearl, that actually made me laugh outloud :laugh:
It's not funny, it's true.
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For me it's always the 5# every 2" estimation on my bows after you've made enough bows to know your tllering results on your bows[45-60 pounds].Now I like knowing this because of heat treating in tiller bows early at low draw length[white woods,avoiding crushing belly wood]and putting together composite components onto a lighter weight in tiller bow to get close to my draw weight at 28".It's a very handy thing to know in bow making.
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If two bows of different wood but the same draw weight(say 40#) shoot the same arrow, will it go the same distance/speed? I'm guessing no, but I've got no good reason. What other factors enter into this?
Thanks
Don
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there are too many other factors in play but I'd say that the type of bow wood is one of the least.
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If the unbraced profile on those two bows are the same, then the arrow speed will be the same, or very very close regardless of them being 2 different woods IMO. One say is Osage and the other Ash, to get them both pulling the same weight and maintaining the same profile, the Ash will take more wood, i.e. wider than the Osage. That is the modifier.
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That surprises me. If that's the case, then why is there so much discussion about which wood to use? Workability?
Don
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Bad example really, you see Osage is magic! So use any other dense wood and the example is in my estimation accurate. The joke illustrates my answer to your question. People have a favorite wood. Maybe because it is readily available in their area, or its density, or color or any other attribute they find desirable, but if you leave Osage out of the equation, wood is wood. Its variability can be greater within a species than it might be to another species. End of the day, unbraced profile tells the biggest part of the story, and you have to treat different woods differently to get them to achieve the same profile. Once you have, I think they will behave similarly.