Missed it by that much

[traditionalman]

I tried to make a 68 inch 40@27 self bow out of hickory. Ed wanted 1 1/4 wide limbs and we thought 3/8 to 7/16 on the thickness of the limbs. I was thinksing that a 2 inch wide limb would be better, but went with the 1 1/4 wide. After tillering the bow string was straight and the tiller looked good but weight was 20 pounds at 27.

How much weight could I expect to gain if I back this bow with red elm or ash backing? If I can not gain 20 pounds at least 10 pounds would be great for my Granddaughter.

I thought of cutting it down, but Ed is 73 and can not shoot a shorter bow. He has to have the lenghtn to get 40 pounds back and does not want to drop down to a 35 pound or less to shoot.

If I did cut 2 inches off each end for my Granddaughter what could I expect to get in poundage increase?

I know this is all a guess but I'm still learning and your guess is a lot better then mine. I have no disc camera at this time and if I get any money I spend it on video, DVD, and books on self bow making so I probably won't have a disc camera for a while.

I do appreciate your advice and help, Also I could also back the bow with more hickory and this is a board bow. I was thinking of 1/8 to 5/32 thick and 1 1/4 wide to 3/8 at the tips for the backing.

[Pat B]

Quit measuring the thickness. With wood bows there is no set thickness. Are you working a stave or board?  You need to tiller the bow to the draw length and draw weight you want and that will determine the thickness the bow should be. After you build lots of bows you might have some ball park on the thickness but until then work down the thickness until you get the desired weight at the desired draw length.
  At least 1 1/2" wide is good for hickory of that length but 1 3/4" would be better. You can always tiller from the sides(reduce width) if the limbs are getting too thin.

[traditionalman]

This was a board board and your answer makes a lot of sense to me. I guess I had a preconceived notion that the limbs x wide and thick = x pounds of bow weight.

I will regroup and try again.

Thanks Again
Gary

[Pat B]

With glass lam bows all lams are engineered to specific tolerances as is the glass. With these bows you can determine how thick it should be for a specific weight at a specific draw length with calculations. With a selfbow the variability between the types of wood, woods of the same specie and even the wood from the same tree makes it very difficult to determine the thickness of a finished bow in any given stave. Like I said after you have built many bows you can get in the ballpark but selfbow building isn't an exact science. You take a chunk of wood, remove everything that doesn't look like a bow and what is left over is a bow!  d;^)   ...more art than science.

[walkabout]

i agree with pat, there really isnt any way to know unless you are copying exactly one design. after making quite a few board bows out of 1x2's, i can roughly guess how thick i need it to be, but this is because im using the same limb width and taper. when you stray from that its really a tossup. if you narrow a limb you have to compensate by adding thickness, and vice-versa. the old adage of(a piece of wood twice as wide is twice as strong, whereas a piece of wood twice as thick is eight times as strong) usually plays a part in my estimates of a thickness needed, but i still start off with what i think is more than i need and work down.