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Main Boards => The Bowyer's Bench => Topic started by: skeaterbait on March 10, 2018, 05:54:00 AM

Title: ?? for the math-heads around here
Post by: skeaterbait on March 10, 2018, 05:54:00 AM

I am getting ready to start another 3 pc take down and wanted thoughts on the stack. What I have ground, when measured individually, come up with a stack of .495. I figure that is kin to being a pry bar rather than a bow, but my plan/thoughts are to make the bow 1.25" wide and taper to 3/8" nocks, with the limbs being 26" on a 17" riser.

I just don't know how to calculate how much stack thickness I should remove to keep this in the 45# range.

Title: Re: ?? for the math-heads around here
Post by: Roy from Pa on March 10, 2018, 06:02:00 AM

.425 should do it...

Title: Re: ?? for the math-heads around here
Post by: kennym on March 10, 2018, 08:17:00 AM

.425 would make a jack handle on my form. Somewhere around  .100 less will make 45-50 with 16” riser .  I’d have to look tho.

Glass thickness, taper rate, power lams, all play into it.

Title: Re: ?? for the math-heads around here
Post by: skeaterbait on March 10, 2018, 08:30:00 AM

Yup, I had every intention of mentioning the taper rate, which is .003. The glass I have is .030 and I haven't come close to wanting to understand power lams   :banghead:

Title: Re: ?? for the math-heads around here
Post by: styksnstryngs on March 10, 2018, 03:06:00 PM

Well, as an Asian, I was gonna use some basic calculus, some integrals and maybe matrices would have been helpful, but thankfully we have Kenny.

Title: Re: ?? for the math-heads around here
Post by: styksnstryngs on March 10, 2018, 03:09:00 PM

Well, as an Asian, I was gonna use some basic calculus, some integrals and maybe matrices would have been helpful, but thankfully we have Kenny.

Title: Re: ?? for the math-heads around here
Post by: kennym on March 10, 2018, 04:40:00 PM

Got home and looked, Lonnie. For 45# my 64" TD takes .315 with .040 glass so you may wanna add some for using .030, for my "guess" I would try about .330 total.

Good luck , heck, I don't even know yer profile or pad angle. LOL

Title: Re: ?? for the math-heads around here
Post by: skeaterbait on March 10, 2018, 05:00:00 PM

Quote

Originally posted by kennym:
Got home and looked, Lonnie. For 45# my 64" TD takes .315 with .040 glass so you may wanna add some for using .030, for my "guess" I would try about .330 total.

Good luck , heck, I don't even know yer profile or pad angle. LOL

You got me thinking there, I wasn't sure I knew either, but I am using a riser I already have made up, 11°. But I am also going to narrow the limbs by .25"

Title: Re: ?? for the math-heads around here
Post by: monterey on March 10, 2018, 05:23:00 PM

My RD has a 12* riser at 18" but the longest built off it was 62".  A .345 total stack came to 49# roughed out.  My stacks are pretty close to Kenny's.  There was a tip wedge that ran 6.5" from the nocks.  

I made it into a 60" so I dunno how it might have finished.

You are probably going to build one for a baseline and go from there just because of design factors.  Shoot for the low side. I'm still trying to figure out what to do with a 100# RD.   :confused: