how to decrown a stave?

[willie]

A discussion on another thread brought up the question of how to properly decrown a stave.

I always thought that if you removed wood from the back, so that the cut ring lines were equidistant apart, then the grain would not be violated. (presuming that the grain does not spiral down the stave)

Are there different ways to do this that work well?

[scp]

I think you got it. I routinely decrown sapling staves. But only using block planes or scrapers. And the grain lines better go all the way to the tips. After that, it should be treated like a board bow. I also rip saplings in half and treat the bottom stave as if it is a "perfect" board bow, instead of a backward bow.

[willie]

thanks scp,

why or better yet, how is a board bow "treated"different than any other bow?

willie

[joachimM]

I work like scp, basically.
Sometimes I split a narrow log <12 cm in four quarters and use the split side as a belly or back (depending on what bow shape I want) and (deeply) decrown the sapwood side, giving four quarter split bias or edge ringed backs staves of 5x3 cm thick with perfectly parallel grain on all faces.
See TBB2 p 28

In ring-porous wood (ash, oak, locust, osage, hickory, elm...) I try to avoid to bring a large part of the softer less dense early growth part of a ring near the back surface when decrowning, especially in the middle as that will run to the tip of the bow where only this weak early wood will be exposed on the back or just be covered by a thin strip of late wood.
I fear this contributed to the break of my latest elm bow. It only had a bit of late wood at the surface...

[Del the cat]

Spoke shave works well too.
You are spot on about having the ring lines running along the limb. I'm currently working on a character Yew heartwood bow that has one side of the back almost following the ring, but thr rings then dive down into the stave and it looks more like quarter sawn along the other side of the back.
Dunno if that makes sense... sorta like two bows stuck together edge to edge, one quarter sawn and one ring backed
What could possibly go wrong? Did I mention the waggles and knots?
Del

[Pat B]

I never understood why one would decrown a stave anyway unless you were going to back it with a hard backing.   

[George Tsoukalas]

scp, is correct. Bowyering is all about the grain even when decrowning.
Decrowning is not just a matter of flattening the crown.
Jawge

[Springbuck]

 The explanations above are simple, and correct, as those above me have said.  The caveats are just that knots and little humps in a sapling stave (and a sapling stave WILL have more of them) can't just be flattened.  In other words, if the sapling's original surface is almost perfectly even and smooth, even if it has little deflex or reflex in the stave overall, then you can essentially flatten it side to side until the ring lines run parallel and you are there.

 But, if there are knots or bumps, esp if the crown wanders side to side, you have to account for that, and can't just run over it flat any more than you can run over a knot when chasing a ring.  However, the decrowned stave would be slightly more forgiving of that.  For instance, much of the elm I work with is absolutely speckled with tiny pins that never even got started to be a branch.  I can just ignore them, but a big lump where the grain curved around a knot on the side of the sapling, you should still have a lump there with the ring lines going up and back down a little bit.

[George Tsoukalas]

Good point, Springbuck. If there is a knot in the back, decrowning is not a good idea because flattening a knot can be fatal to the bow. Jawge

[scp]

why or better yet, how is a board bow "treated"different than any other bow?

I mostly work with hand split staves. Once the bark is removed and the stave is narrowed by splitting the sides off, I don't worry much about ring violation, even for pyramid style or molly type bows. But with board bows, I would watch out for grain runoffs more carefully while designing the front profile, not just on the top but also on its sides. With staves, we never have to worry about runoffs on its sides.

[joachimM]

Good point, Springbuck. If there is a knot in the back, decrowning is not a good idea because flattening a knot can be fatal to the bow. Jawge

I fully agree with Jawge.
You're right that decrowning can be a tricky business.