Taper vs. Parallel in Longbow Stack

[SenterShot]

I've made a few recurves with .002 tapers following the Bingham pattern...they all begin to stack at 29".

I'd like to build a Hill-style glass laminated bow next, and I'm wondering what effect a taper would have in the stack.

If I'm aiming for a 50 - 55# range with 1.5" limbs and 70" overall length (what's a longbow if it ain't l-o-o-ng?), what stack thickness would ya'll suggest?

[jsweka]

How long will your riser be?

[SenterShot]

I was thinking about making it a 16" riser.

[jsweka]

Bingham's straight longbow design call for an 18" riser, 1.5" width at the fades, 68" length, and a 0.404" stack.  That's with 0.002 taper.

Decreasing the riser length and increasing the limb length would increase the working length of each limb by 2 inches (4 inches total).  That would decrease the weight by 8 - 12 pounds.  Using that lam stack calculator spreadsheet BJansen developed, I would increase the total stack to about 0.432".  Of course you never really know until that first one is built.

[bigbob2]

I use a 16'' riser with the HH style long bows I make and use 4 x .001 tapered lams  in each. Going by my force draw curves they show absolutely no sign of 'stack' even out to 31'' and are very smooth.They vary in length from 66'' to 68'' Nock to nock

[Brianlocal3]

Thank you for that bigbob

[fujimo]

if you dont mind me asking,what is your total stack thicknes bigbob, and are you using any other overlays(power lams) etc at the riser or tips.
thanks
wayne

[7 Lakes]

1.5" wide at the fades is pretty wide for a Hill Style.  Add taper if you decide to decrease the width.

[bigbob2]

Mine are 1 1/8'' at fades, 1/2'' at nocks, and for 50# - 55# depending on veneers used, around .400 for wood alone using .040 glass. This is about the limit of .040 glass weight wise.In the HH style no power lams any where.hope this helps. This is my approach and others will have a different way which no doubt will work very well.

[SenterShot]

Bigbob, when you say you use four tapers, do you mean two in each limb, or a stack of glass-taper-taper-taper-taper-glass? Is there a benefit of using all tapers without parallels as opposed to accomplishing the taper in one lamination and filling out the remaining thickness with a parallel?

Since I'm starting to sound like a four-year old ("Why? Why? Why?), for those who combine a taper and parallel, is there a common ratio of thickness between the two, similar to the rule that glass ought to be 25% of the stack?

[bigbob2]

Four tapers in the lay up each with .001 per running inch and then the 2 glass on top of that or more correctly one each side of the lay up.I feel personally that the lams all being tapered gives a very smooth progressive 'feel' to the draw.Others will swear by their personal method be it a combination of tapers and parallels or one taper and the rest parallels. Unless there was a comparative study done utilizing force draw, chrono etc then it will just come down to personal opinion and choice.

[monterey]

Sentershot-  If you stick with Bingham on your first you would do well.  Even if you reduce the riser length, the reduction cited above should keep you out of trouble.  

You will not *need* a 70 inch bow to get good performance.  Like bigbob2, mine (bingham formula and materials) stretch out beyond 31" in the fd curve without stacking.  That goes for 66", 68" and 69" lengths.

with the Bingham formula(.002 taper), when you start getting under 1.25" wide, you will get into problems of the outer limb overpowering the inner limb.  You may not readily notice it, but it will begin to happen and will get progressivley worse as you make it narrower.  

I took one down to close to 1" and even after narrowing the limbs to pretty much a pyramid shape they were still out of whack with the limb bending way to much near the fades.  Had to sand taper into the glass to correct it.  Was no prob since it was just a 42# bow and had .050 glass on front and back.

I'll just say to stick with proven formulas either Bingham or trusted members of this forum while starting out and do your experimenting$$$      after you get a few under your belt.

[SenterShot]

If only one taper is used in a straight longbow, what ratio should there be between between the taper and parallel? So for example, a stack of:

2 pcs 1 1/2" fiberglass with a thickness of .050"
2 veneers @ .025"
1 parallel of bamboo @ .100"
1 taper of bamboo with a .002" per inch taper starting @ .182"

Or is it more common to maintain the taper at .130 or .140 and beef up the parallel to get the desired stack thickness?