A break along (or, where did I go wrong???)

[knuklhed]

So, I figger I'm gonna build me another long bow. I have some Ipe deck boards, some maple for the core, and hickory for the back. I grind them up, arriving at .255" parallels for the belly, .180" maple with .004"/in. taper for the core, and .130" hickory with .002"/in. for the back. All of the wood seemed good, the ipe was not perfect quartersawn, it was at maybe 60*, and the maple and hickory were both closer to a perfect 90*. I'm using the same form I used last time, a mild D/R. Glued the limbs up with UB 800, cooked it overnight, all good so far. I clean it up, and start on the riser, hard maple. Then, as I'm looking at the pic of the forward handle I've got pasted up on the tillering board, I decide, why not? and try to mimic that. I think this may have been where I went horribly wrong. I put the bulk of the riser on the back, and a backing strip on the belly, and proceeded to try and finish it out. I got the limbs shaped, tips put on, and got to the board, exercised it, pulled eventually just past 7", and it was looking good, so I figured I would go ahead and start the shelf before I finished tillering (another screw up). After I rough cut it in, I put a couple of twists in my tillering string to try and get to a low brace, and used my stringer to put the string back on.  SNAP!   I can see the glue joints did not fail, the wood did. Any opinions, is it because the back couldn't stretch through the middle of the bow with the riser holding it? Or the belly could not compress enough? When you are making a forward handle, is it vital to put the back and core over the riser back, and run the belly up on the belly side? What don't I know that I don't know?   Thanks for any advice, I'd really like to make this style of bow work, I like the lines of them a lot.

[knuklhed]

Oh, and the last picture is me holding it open a bit to illustrate where the breaks were. This is the other side of the break.

[Stagmitis]

Looks like your fades are too steep to me. Lots of compression there and it needs to gradually bend.

[Roy from Pa]

I'm not so sure a forward handle design is feasible for an all wood bow.

Anyone else ever done one?

[mmattockx]

Looks like your fades are too steep to me. Lots of compression there and it needs to gradually bend.

It failed on the back side, though. I do agree the fades could be feathered out better.

I'm thinking it needed a power lam under the handle to stiffen that area up a bit. Doesn't take much, even just 0.080"-0.100" will make all the difference for the glued on riser pieces.

I'm not so sure a forward handle design is feasible for an all wood bow.

Anyone else ever done one?

I'm not sure if you would consider this a forward handle design, but the front riser piece was about 7/16" thick and the limb lams carried on straight through the riser area. I see no reason it couldn't be thicker and work fine.




Mark

[knuklhed]

I did use a small piece of maple on the belly as reinforcement/power lam, maybe it should have run the same length as the "riser"? And, I need to keep trying on getting the fades right, this isn't the first time I've blown one up. I just haven't figured out how far to fade it before making the sharper curve up to the meat of the riser.  Thanks for the input so far..

[mmattockx]

I did use a small piece of maple on the belly as reinforcement/power lam, maybe it should have run the same length as the "riser"? And, I need to keep trying on getting the fades right, this isn't the first time I've blown one up. I just haven't figured out how far to fade it before making the sharper curve up to the meat of the riser.  Thanks for the input so far..

The power lam needs to be inside the lam stack to work. You want the stack to get thicker coming into the handle so the stresses on the back and belly surfaces are reduced a bit before they get to where the riser pieces are glued on. In the bow I posted the pic of there is a 0.080" thick power lam under the back lam. It is full thickness for the full length of the external riser pieces (about 10") and then tapers to nothing over ~3.5" out into the limb.

For the fades, in the pic mine has a smooth, constant radius from zero thickness up to the full depth on both the belly and back pieces. If you want to have a step in that taper I wouldn't start it until the total thickness (handle + limbs) is twice whatever the limb is just before the fades start. At that point the stresses will be 1/4 of what they are on the limb and you shouldn't have major problems with it wanting to come loose.

This is how thin I taper the fades on mine (not the same bow, but the same style):




Mark

[Longcruise]

Along with thin at the tips, the rate per inch is also important.  The common rule of thumb is that the fade should be no thicker than 1/16" at one inch from the tip.  That has always worked for me.

[kennym]

I'm far from a wood bowyer but it looks to me like the belly fade is bending and the back fade is much thicker there so not bending?

[Roy from Pa]

Yup and that's why it broke there.

[Pat B]

It bent too much into the handle. A power lam would have probably prevented it.

[knuklhed]

Thanks for all the replies. I guess it is time to start grinding up some new lams, add a power lam to my stack, and continue working on my fades. I'll post up in a while with the fresh attempt. 

[Roy from Pa]

Make one like this:)

[knuklhed]

Second go round, this time .190" 1/4 sawn Osage parallels, .156" 1/4 sawn Maple (.002"/in) cores, .150" flat sawn Hickory (.003"/in) back, with a hickory power lam that's 1/8" in the center, and tapers around .011"/in down to 0. Riser is about 15 3/4", power lam is 22". Cut that riser back off the broken bow, cleaned it up, and tried to make the fades more drawn out, and put the slightly shorter overlay back on the belly side with a 4" straight section in the grip, then slight radii to the ends. Just cut the limb profiles, and will be putting overlays on this afternoon. Here's a picture, any insights, critiques, before I go further? I can always take more wood off the fades if I need to before starting the tillering process.......

[knuklhed]

I made some progress without any more carnage, so far. Here are some pics of it, unbraced profile, then braced, and at full draw. Lower limb is to the left on the tree. The rope draws down straight, even though the limb profiles aren't a mirror image of each other. A bit more shaping of the grip and tips, and then I'll put some arras through to see what it feels like. 68", 37# at present.

Tiller opinions?

[Roy from Pa]

Looks real nice....

[knuklhed]

Thanks, Mr. Roy. I owe any success to the collective wisdom of TG. Without it this blind pig may not find any acorns.