Max draw weight for board bow

[Rain Man]

My 3rd board bow was almost complete.  I wanted it to be a beast.      :D      So I picked out a 1 x 3 of oak and cut it to 70 inches.  I also used a 1/4 inch thick strip of straight grained red oak for backing.  I had it braced and tillering was perfect to 24 inches.  With my first 2 bows, the tillering wasn't the best, but they still shoot good... and honestly, this tiller was perfect.  So anyway, my scale said 50 pounds at 24 inches.  I figured instead of exercising the limbs on the tillering tree, I would just do it by hand.  So I pulled it to what I thought was 24 inches a bunch of times, then I went to pull it to full draw at 28".  SNAP.  4 pieces went flying.  It snapped at mid limb on both limbs. If I had to guess, 50 pounds at 24" would probably make it well over 60+ pounds at 28".

My question is what is the highest draw weight you have done with a board??  Is there a limit?  I just don't understand why it failed when the tillering was so much better than my successful bows before it.

[Eric Krewson]

I always backed my oak bows with a strip of hickory, never had a failure.

[walkabout]

i had one pulling about 55#@28" but i had to reduce it for the intended owners draw weight. after i scraped the limb split and went flyiong across the shop.lol.the bow you mentioned probably broke due to the 1/4 inch backing. you only need about 1/8" thick backing or the belly wood gets crushed under tension.also remember you gotta slowly excercise the limbs up to the intended draw length, because the wood fibers need to get compressed enough as you go otherwise they get compressed all at once whan you draw the extra 4 inches and bad stuff can happen.lol. i have a 72" red oak that pulls 49.5#@28, and another that pulls about 50#@28. the 50# is a 60" bend through handle i just got done. all my bows are built with the 1x2 not the 1x3, although im going to try a pyramid style next.

[walkabout]

backing grain also has to be perfect with no runoffs at all or it will fail but im guessing it was just too thick. try using hickory or even silk backing and see if you have luck with it,i personally have used brown paper with success, and burlap but i dont like burlap very much for a few reasons. good luck. oh also check out jawges site, he has some good pointers for board bows on there.

[DesertFox]

Try using hickory. The third bow I ever made was a hickory board bow and it tested 60# at 28". I have no backing on the bow with 1 or 2 runoffs near the handle (if the grain ran off any farther up a limb, I would not have tried for such a high draw weight).

The key is slowly tillering it. If the bow doesn't bend equally throughout, it increases the chances of failure. Especially at a high draw weight. Perhaps the slow tillering helps compress the fibers as Walkabout was saying.

[George Tsoukalas]

There are 3 important things in making a board bow. 1. grain, 2. grain and 3. grain. A better question to ask is how much weight can the board you have chosen yield. Straight grained stock probably 100+. Jawge

[Rain Man]

The main board had a few runoffs, but my backing had none at all.  I think my problem was what Walkabout said.  Since the backing was 1/4 inch thick, the backing was either equal to, or thicker than, the main board itself because my total limb thickness was about 1/2 inch.  I won't do that again!  Rookie mistake

[Loren Holland]

everything said above is correct, and i think the combination of not excerising it into the last four inches of draw, and that backing being too thick was the death nell, but one other thing to consider...what was the MC.  I had a hickory backed hickory blow up (don't laugh), because i didn't stop to think that the cabinet shop i bought it from was using kiln dried wood that was probably way under 8% at the time.  its a small consideration compared to the other two factors, but think about this in your storage of your boards and before you start work on one fresh from the store.
i will tell you that the backing thickness is relative, but extremely important. i found out the hard way when i switched matls from hickory and oak.  on one of my first bamboo backed ipe bows, i didn't thin the bamboo enough, and ended up with a broken, thin piece of ipe glued to a bamboo lam

[limbcracker]

If you are using planed wood, from a hardware store or lumber yard, the real thickness is usually 3/4 of an inch, with such boards 2" wide, you usually can't get a bow much more than 50lbs, even from hickory before, it starts to bend through the handle. If you laminate a piece of 1/4 to 1/2" thick, 8" to 12" inches long to the belly side flat of the handle, you can made a 5 to 10lb heavier bow, (or add weight to a bow that turned out lighter than you wanted).