Encyclopedia of NA Bows?

[randman]

Here's a simplified illustrated description of what you are asking. Makes more sense when you see a picture of it.

[TimBo]

What causes problems is when the wood fibers are compromised/cut; keeping the back as one complete ring is the easiest way to keep undamaged fibers, but not the only way.  The board bows chapter of TBB II is probably the best visual explanation of this.  Decrowning makes the back of the bow look like an edge grain or quarter sawn board with straight grain; the grain and fiber lines run parallel to the edge of the board/stave. 

[TimBo]

...like randman said just before me with a very useful illustration!

[steve b.]

Sasquatch,
If you are wondering about a, "completely flat back" then yes you are right there's rarely a truly flat back along the entire length of the stave or bow.  Its just a concept that you keep in mind when designing or building a bow. 
However, there are "flat" backed bows because if you look at any tree cross section you will often see that, even though the tree appears round, it really isn't, because as you look at the rings you will see flat sections of the circle that the ring creates. 
So a 1 or 2" wide bow can have the appearance of a flat back even though, had you chased the ring perfectly, you can lay a straight edge across it and see that is does indeed curve or round at the edges.

[PatM]

I doubt the artist took actual profile measurements with one of those thingamajigs that measure that.
 I wouldn't be surprised if the bows depicted from woods suitable for decrowning are not actually decrowned though.
 It is not too hard to find a tree with at least one flat side. Often trees growing in a situation conducive to that actually will have a slightly concave back.

[Comancheria]

Marc,

I think you were exactly correct about my misunderstanding of the concept--that is, until
I saw randman's excellent illustration.  Don't want to continue to jack this thread, (and I may still be off base) but it seems to me that it is OK to cut through the back rimgs--so long as thou carry that grain line all or most of the way to the ends of the stave.
Thanks!

Russ

[JackCrafty]

I've looked at those illustrations many hundreds of times since I got those books several years ago and all I can say is that each bow must be evaluated separately.  Many bows have rectangular cross sections, yes, but they are not all made the same way.  Some are decrowned, some are biased ringed, some are made from large diameter logs, and some have violated rings.  Some are very short draw bows and some have very long draws.  Many are made from Hickory which is very forgiving of grain violations.  And some of the illustrations are just plain inaccurate because of a lack of data, for example.

The thing to remember is that a rectangular cross section is very safe and many bows will be made this way by default.  From what I have seen of the real things, the bows are made from the best piece of wood available.  This usually means the backs are very clean and free from lumps, high crowns, and/or undulations.

[randman]

Yeah they didn't mess around back in the day with the snakey, roller coaster, character stuff we all got time to mess with....feeding your family was serious business and bowmakin wasn't just a hobby....Jackcrafty, the list of bow styles you mentioned sounds a lot like this forum.   

[George Tsoukalas]

TimBo, gave an excellent description.

The purpose of decrowning is to counteract heavily crowned staves which concentrate too much tension right down the middle.

Decrowning requires some finesse and time. The payback is not all that great and it is easy to make a mistake  and violate that longitudinal grain.

In the past I just left heavily crowned staves a  few inches longer.

I saw some decrowned or board bows at the Harvard's Peabody Museum. To me they looked to be bows made from boards.

Jawge

[Marc St Louis]

The illustrations that Rand posted are good and a properly decrowned stave would be #2