Why trap? Are there different ways to trap? What about Decrowning?

[willie]

Usually take a bit more set though.
Arvin

Arvin,
that's comparing identical flat bow cross sections, one made from a small diameter tree, and the other made from a large diameter tree?

or comparing two limbs of a given width, one trapped, and one untrapped?

[Selfbowman]

DC I have been moving mass around in specifically Osage bows for some years. Trapped back and belly
Even in pyramid bows trying to eliminate set. Put more mass at fades , thicker non bending outer limbs, wide at the fades etc. anything and everything for faster smoother bows. Not sure I have found the answer yet. I have had the time of my life building these bows. Arvin

[Jim Davis]

Well, lots of right info above, but the facts are even more intense. All wood is stronger in tension and most wood is at  least 3 times as strong in tension.

Any gain in narrowing the back of a bow is due to reduced mass, since the limiting factor is already  the resilience/strength of the belly.

Decrowning in an effort to strengthen the back is wasted effort on all but very small sapling staves. The back is already stronger than the belly. Except in the case of violated growth rings, bows always chrysal on the belly before they break on the back.

I have a demonstration kid's bow that is 3/4 wide at the fades,  tapering to the tips. It has a 1/16 thick hickory backing that is only 5/16 wide the length of the bow. It shoots fine and has no string follow.

[willie]

Not sure I have found the answer yet. I have had the time of my life building these bows. Arvin

Arvin.
that's what is all about with a hobby, getting some enjoyment.  Since you work almost exclusively with Osage, and it has unique properties when compared to other woods, I suspect when you find the answer, it won't be a "one size fits all" kind of discovery.

Any gain in narrowing the back of a bow is due to reduced mass, since the limiting factor is already  the resilience/strength of the belly.

So in the case of a wood lam bow, a lighter in density, (but full width) backing will accomplish the same effect? I think it could actually work out better than narrowing, as the back strain can be spread out over a wider area.

[Sagebrush]

I use decrowning for OS.  It helps me to get a wider stave.  I can take a stave that I would only get 40lbs from and get to over 60.  This also solves problems with pesky pin knots.  I then back with rawhide or silk.  I just eyeball it, you can't follow a ring as I do with hazel.  I would like to try vine maple at some point.

[DC]

I use decrowning for OS.  It helps me to get a wider stave.  I can take a stave that I would only get 40lbs from and get to over 60.  This also solves problems with pesky pin knots.  I then back with rawhide or silk.  I just eyeball it, you can't follow a ring as I do with hazel.  I would like to try vine maple at some point.

Is there a particular diameter OS that you decrown or do you just do all of it?

[willie]

following ring lines in birch is challenging as they are not very apparent to the eye, I am still experimenting with some stain on a rag between scrapings.

[DC]

If trapping balances the back and belly better is there any chance that trapping an existing bow a bit won't affect the draw weight? I know that seems like a free lunch but i thought I'd ask

[George Tsoukalas]

I leave saplings a few inches longer to counteract the crown. What longer means depends on your draw length. Jawge

[Jim Davis]

If trapping balances the back and belly better is there any chance that trapping an existing bow a bit won't affect the draw weight? I know that seems like a free lunch but i thought I'd ask

Could be, within limits. Might be a good experiment for somebody.

[DC]

One scrape at a time until I see what's happening I guess

[mmattockx]

If trapping balances the back and belly better is there any chance that trapping an existing bow a bit won't affect the draw weight? I know that seems like a free lunch but i thought I'd ask

This is from my engineering experience, but I know of no way to remove material from a beam (really from the cross section) and not reduce its bending stiffness. Trapping 'a bit' won't do much in terms of reducing belly strains and it also won't make the limb much weaker, either. The two go hand in hand, so the more you help the belly wood the weaker the limb will get.


Mark

[DC]

Thanks Mark. I was thinking that since the boo is so strong that the "beam" might not notice if a bit was missing . Just going for a lighter limb. I will trap the recurves. I've done that before. I guess because they are static(strong)they can stand to lose a little.

[Corvus]

If trapping balances the back and belly better is there any chance that trapping an existing bow a bit won't affect the draw weight? I know that seems like a free lunch but i thought I'd ask

Think it would really depend on how much you trap and the woods of the bow plus construction. In theory I would expect most cases to be something like slight DW drop with slight improvements to cast and arrow speed, but not much changed overall. Would definitely be an interesting experiment

[DC]

Interesting but unsuccessful. I had a bow at 203 and I had to be greedy. I made a new string, dropping the weight from 57 to 41 grains. Speed stayed at 203. Trapped the recurves/tips, speed stayed at 203. Trapped the last 8-9", just a couple of scrapes. Tested the draw weight. It had dropped 3 pounds and there was a big hinge in the bottom limb. That quick. Chronoed it anyway 199. And again 197. It's going away and it's also throwing the string. Darn. My last good piece of Yew. In hindsight though if it only took a couple of scrapes to ruin it, it probably wasn't going to last anyway.