Need advice.

[Buemaker]

Sometimes there is a complete stand still in my head so I need some help. I glued up a glass RD bow that came out about half the weight that I wanted. Now in order to double the weight how much thicker should I go? I think I read somewhere that if I double the stack thickness the bow will be 8 times as strong. If I add 1/8 of the thickness of the bow that came out too light, will I then be in the ball park?
Thanks.
Bue square head moroon.  

[Robertfishes]

I'm away from my bow build log book right now..On a KennyM design D/R bow every 0.003 will make aprox 1 pound difference. Is this bow the first off of the form?

[fujimo]

try this, works pretty well
www.facilityautomation.com/hosting/Lam%20Stack%20Calculator.xls

[monterey]

Ditto on the stack calculator.  It has been dead on for me.

[Buemaker]

Thank you. The bow that came out light was the first off the form and had a stack on 0.320 at the end of the fade outs. It came out at 25lbs and is an RD  with .003 taper and 19" between fades and 66 ntn. The stack calculator suggest 0,418 in order to get 55lbs. I will try that and see what happens.

[LittleBen]

So let's say you wanna increase weight by 50% ... So the second bow will be 150% of the draw weight of the original bow.

take the cube root of 1.5 (which is about 1.15) and multiple by the original stack to get the new stack.

If you wanna double the weight it's the cube root of 2 (which is about 1.25) multiplied by the original stack.

[passion for knowledge]

All else being equal, width/weight is a linear thing - thickness is a third power deal.

Terrible description....

If you reduce the width by half, you will reduce the weight by a half.

If you reduce the thickness by a half you will reduce the weight by 2 to the power 3 - a factor of 8

hopefully that's a bit better.

[fujimo]

knock it off you two     - i can barely find the stack calculator on the web- never mind those calcs!!!
dont confuse my little brain any more than it already is. damn technowizards anyway  

[canopyboy]

Originally posted by LittleBen:
So let's say you wanna increase weight by 50% ... So the second bow will be 150% of the draw weight of the original bow.

take the cube root of 1.5 (which is about 1.15) and multiple by the original stack to get the new stack.

If you wanna double the weight it's the cube root of 2 (which is about 1.25) multiplied by the original stack.

Agreed. The stiffness of a beam in bending is function of the width multiplied by the thickness cubed just like Dave said. If the width is being held the same (and of course the length), Ben has your answer.

[fujimo]

Yup x2- exactly what i was going to say Dave  :confused:

[Robertfishes]

Sometimes you don't know till you build it.. If you do the math I think the stack calculator numbers and Bens formula will be very close..both pretty much .0032"/lb, you will know more once you glue one up