Bowyer Help - Please!!!!

[huntwithastick]

Please offer a solution if you can:

I ordered a limb lamination kit for a pronounced TD longbow from Binghams with a target of 62" with a 15" Riser (9" from bolt to bolt) and 45 lbs @ 28".  Based on my calipers, I received

back/belly glass: .050
belly taper: .002 per inch, .1" @ thick end (butt)
parallel: .003
wedges: 8.25"
reverse taper: .002 per inch, .12 @ thick end  
 (tip)

My limbs ended up a little under size compared to the template.  They finished 1.3" wide at the fades and .68" at the nocks.  The limbs are 27" from nock to center of bolt hole and the bow finished @ 30 lbs and 61".  

Question #1:  Was I far enough off target to account for the 15 lbs deficit on my target weight?

Question #2:  If I want to keep the exact same dimensions but come in at 45 lbs., how thick should my laminations be?

Any help would be greatly appreciated.

Doug

[Crooked Stic]

I was thinking the Bingham risers are 17 in. Paralwll .003? .030 maybe ?

[Coop]

I found one these T/D longbows a little bit of limb width can a account for a quick drop in weight. I went from 1 1/2" to 1 7/16" width and dropped a couple pounds. So nearly a 1/4" could have caused you to miss weight.

[huntwithastick]

Their design template is for a 17" riser, but when I ordered the lams I indicated a 15" riser.

Crooked Stic: I believe you're correct on the measurement.  Thanks.

[ChuckC]

I am thinking that you do not have enough limb thickness at the fade.  I think if you would have placed that second taper as a reagular taper and not reverse you may have made it.
ChuckC

[ChuckC]

I am also guessing that you do not need a reverse taper in a long bow limb to stabilize it.  Seems to me it just adds mass outboard on the limb that you don't want.   Actually, if you have a taper and a reverse taper of the same degree of taper, you negate the taper effect and end up with an expensive parralell.

I have made several bows using nearly the specs you describe except no reverse taper and have gotten between 40 and 48 pounds.
ChuckC

[huntwithastick]

Chuck,

I laid them up the way suggested in the Binghams instructions; I believe the reverse taper stiffens the tip end of the limb.  I think this allows the limb to recover faster.

I like my limb dimensions and want to try and hit my target weight once I can determine how much thicker to go on the total thickness.  I didn't include the thickness at the fades and I think that's probably necessary for someone to determine if my lams weren't the right size.  The thickness at the fades is .27" and .26" at the nock.
 
Thanks.

[Crooked Stic]

You are really gonna have to make another set of limbs everything being the same except add more lam thickness to see what the difference is. Then you have something to compare. You can then figure how many thousandths it takes the make a pound of draw weight. My guess is .0025 to .003 is gonna be close.

[PV]

I just measured one of mine and it spec'd .33  @ butt and tip,1.35"wide,66" NTN. 17" riser 11" between the bolts.This bow is #58 @ 28.Did you build the form with the pronounced blueprint? The shallow T/D takes a thicker limb to get the same weight.I'd call Binghams and talk it over with them. I'm sure they can help you figure it out.
Good luck
Paul

[ChuckC]

Doug.  
do this.  Lay your tapers on top of each other (on paper, drawing)  As you layed them into the bow.
One has a butt of .100 the other .120.  The tapers are 36" long (it actually doesn't matter how long they are).  At .002 taper per inch, each one loses .072 in the run.  Subtract .072 from the .100 and the calculated thickness at the end is .028.  On the other one .120 minus .072 is .048.  lets add up the thickness of each end when layed up together...
 
.100 + .048 = .148     .120 + .028 = .148  Unless I figured wrong, that makes it a parallel piece.

When calculating the weight pull in terms of thousanths of an inch thickness, inverting that taper as you did made the difference between .278 thickness at the base and .350 thickness.  That will certainly make a big difference.  Taking a 1/4 " off the sides of that bow, especially at the riser may affect it 5# but I really doubt even that.  

Calculate as I did and see if that makes any sense (and if I added correctly).  I know Bingham's talks about reverse tapers, but it makes no sense in my mind (for a longbow).  You want the tip to be lighter in weight so it responds quicker, not heavier.

Guys...if I did this wrong, please jump in cause I can always learn, but I think this is right on.
ChuckC

[huntwithastick]

Chuck,

I like the way you think!!  I did the same thing.  Here's what I came up with:

back glass: .500
belly taper: .1 @ thick end
parallel: .03
reverse taper: 1.2 @ thick end (.048 at thin end)
belly glass: .500

I ended up with .278 total thickness which, according to Bingham's bow draw weight chart, falls between 40 and 45 pounds for the pronounced longbow.  

I think I'll order my next lams 15 pounds heavier and see where they come in at.  As Crooked Stic mentions, that will give me a comparison to work from.

I'm not all that dissapointed, as I was making the bow for my oldest son but now my younger son can shoot it!!  I'll post a pic here in a few minutes to show you guys how it turned out.  Thanks and if anyone has other suggestions, please keep 'em coming!

Doug

[sidebuster]

Doug if having this bow to be 45#s is important and not making another one you could cut 1 inch on each end and your weight should go up.