Recurving board bows? Kerf cutting for recurve?

[DC]

I don't understand. It looked like you were there. Did you try to bend it more after the glue up?

[Onebowonder]

Lessons Learned:

1] We should NEVER have done this first effort on a stave that had promise still. (duh!)
2] We attempted a curve that was probably too aggressive for this method. 
3] Sanding off the belly side split AFTER we had cut the kerf left one side considerably less thickness than the other.  The kerf should be in the center of the limb so that the two sides of the kerf are pretty much equal in strength before bending them.
4] The insert lam was made of some very dry (read as - STIFF and brittle Walnut).  They should probably have been more flexible.
5] Especially tight radius kerf bends should probably be made WITHOUT an insert lam altogether.

There may have been more lessons to learn from this experience, but these were the ones we were pretty clear on.

We are not done with experimenting however.  The next day, we boiled a wide piece of Sweet Gum and bent it over another caul.  Next stop, ...Siyah town!

OneBow

[Onebowonder]

I don't understand. It looked like you were there. Did you try to bend it more after the glue up?

No, we used the heat gun to 'pre-bend' the osage dry before the glue up.  But when we tried to go for the full bend at glue-up, it all burst.  Pre-bending may have been an error as well, since the heat might have hardened (aka 'heat-treated') the surface of the Osage.  Live and learn...

OneBow

[Springbuck]

I'm with DC, I thought you had it.  Honestly, the tip of the bow was still pretty thick, but your swa work looked stellar.  AND, I don't understand how it broke after you had such pretty pre-bending done

[DC]

I'm wondering if the walnut had gone right to the end if it would have survived? I don't know how you had it in the caul but the end of the walnut would be a big stress point if you were bending it there.

[Onebowonder]

I'm wondering if the walnut had gone right to the end if it would have survived? I don't know how you had it in the caul but the end of the walnut would be a big stress point if you were bending it there.

Yeah, the pictures don't show it very well, but during the glue-up stage the walnut taper did go all the way from the tip of the kerf line to the end of the limb.  They busted up pretty badly as we bent them into the caul during glue-up attempt.

OneBow

[Springbuck]

Maybe that, like it over hung too far?  I have had a couple failures when the kerf was all uneven itself.  Like where, by the time I got the saw marks sanded out inside the kerf there were places it gapped 1/8" and places it gapped 3/16". Also, a couple where I tried to jam a just barely too fat shim in, and it cracked open in the bottom of the kerf.

Neither of those should have happened here.

[DC]

Maybe steam and also bend the insert? I was thinking this would be the answer for major hooks. And if you bent the halves one at a time it would give you better access to sand the inside of the kerf.

[bradsmith2010]

they look to thick to me,, osage is osage,,its the thickness of two bows or more

[bubby]

3Here's a little tip, on short thin wood wrap it in a soaking wet towel and nuke it in the microwave for 3-4 mins bends like butter

[PlanB]

Zooming in a little, pre glue-up, I'm thinking this was the start:

[Dances with squirrels]

If you would have posted pics prior to glue up, I would have predicted that failure. You pushed it too far on too many levels. Oh well that's how ya learn, and hindsight is 20/20. The kerf wasn't accurately cut, and there was a serious shuck and jive in it where it broke.  The pieces were too thick, except where Patrick ground it down for brush nocks... that was way too thin and violated the grain/rings on the belly side. The bend radius was to small. You didn't leave it much choice. It HAD to break :^) He should have waited until afterwards to do that grinding.

Compare yours to mine on page 1. Since that bow, I have reduced the size of the bend radius some, but not to the degree you attempted.

Any time you kerf, you should fill the void with an appropriately sized piece... do not eliminate the lam because of radius.

[Dances with squirrels]

I hate to 'beat ya up' any more, but I felt the need to mention... while it may not have directly contributed to the failure, your walnut lam insert was sub par. I wouldn't put something like that in a limb for that purpose. I use only straight grained, clear, sound, same species, same or better quality wood for such inserts. May not mean do or die, but I do it anyway

[Onebowonder]

I hate to 'beat ya up' any more, but I felt the need to mention...<snip>

Thanx for your input Mr. DWS.  I don't feel the least bit beat up. - OneBow

[Onebowonder]

<snip>...and violated the grain/rings on the belly side.

Are you suggesting that we needed to chase a ring on the belly side of the kerf?  That's not one I would have even thought of doing.  Hmmm...  I guess I see how it might help though.

The bend radius was to small. You didn't leave it much choice. It HAD to break :^) <Snip>

Yeah, that's kinda what we came to on that one too.  Oh Well...

<snip>Any time you kerf, you should fill the void with an appropriately sized piece... do not eliminate the lam because of radius.<snip>

Yeah, that idea came from someone else that's done a few of these.  He apparently makes fairly sharp hooks with the Kerfing method and leaves out the insert for those tighter bends.  I thought it might help some, ...but what do I know???...   

OneBow