Trapping

[Jim Davis]

Contrary to a post above, Badger has had a lot to say about  trapping. He and I have also had lots of off-forum exchanges about it.

Bottom line, any improvement in performance is probably because of less mass in the limb.
 
The thing is, a trapped back does not stretch more before breaking than a full back. The back, if  intact, will always fail AFTER the belly fails. Test results I have seen said that wood stretches only about one percent before failure.

Statements above about relative strength in tension and compression are correct. Almost all wood is at least 3 times stronger in tension than in compression. So, reducing the width of the back is still going to leave the back far stronger than the belly. BUT, narrowing the back in an area where the width tapers makes the grain run off the sides even more abruptly in that area. I have had several failures where the surface lifted where the "trapped" limb narrowed at the tip.

I think there is merit in the idea that string follow might be largely the result of shear in the neutral plane, but I have no evidence or even a way to get evidence.

[bradsmith2010]

ok I would still like to see some specs on how a trapped bow performs,,
has anyone done any testing,, 

[Wooden Spring]

BUT, narrowing the back in an area where the width tapers makes the grain run off the sides even more abruptly in that area. I have had several failures where the surface lifted where the "trapped" limb narrowed at the tip.

I think there is merit in the idea that string follow might be largely the result of shear in the neutral plane, but I have no evidence or even a way to get evidence.

Very true, trapping a bow does make the grain run off the sides more abruptly, but rounding the corners of the bow reduces the tendency for splinters to lift somewhat, but this technique may be better suited to backed bows if grain runoff is a major concern.

As to the evidence of sheering forces in the neutral plane contributing to string follow, I wonder if we can get a bowyer willing to attempt Forrest Nagler's "Heavy I-Beam" construction a try? Any takers???

[Wooden Spring]

ok I would still like to see some specs on how a trapped bow performs,,
has anyone done any testing,, 

You and me both... The test would require two bows be made from the same tree, and given the exact same construction parameters, except one bow, before tilling is given a trapezoidal cross section where the back is given about a 10-15% reduction in width compares to that of the belly. The comparison would have to be made on a force-draw curve to demonstrate each bow's efficiency.

[bradsmith2010]

I dont really need a compison, that would be nice,,
but just to see how a trapped bow shoots,,
can they shoot as well as normal self bow,,the same,,, better ,,, something???
If I had a trapped bow, I would shoot it with a 10ggp arrow just to see how it was doing compared to other self bows in general,,
 

[Wooden Spring]

I dont really need a compison, that would be nice,,
but just to see how a trapped bow shoots,,
can they shoot as well as normal self bow,,the same,,, better ,,, something???
If I had a trapped bow, I would shoot it with a 10ggp arrow just to see how it was doing compared to other self bows in general,,
 

I don't know that you'll see a difference in cast...  Trapping the back won't make it shoot any faster, it's just a method intended to prevent uneven fiber stress. If it's something you want to find out about, just build one and then tell us about it.

[Jim Davis]

I trapped all my bows for a decade or so. I could not compare them with untrapped, but all seemed to have good speed and low hand shock. The latter I attribute to the fact that they were all pyramid design as well as trapped.

If I had access to a chronograph, I'd test a bow, then trap the limbs and test again--but I don't.   

[bradsmith2010]

I see your point,,
I just see alot of speculation about the benfits of trapping,,
but no stats to back it up,,
I dont need to build one to find out,,osage really doesnt need it  ,,,was curious if anyone claiming benefits from trapping had ever tested a bow,,
maybe they shoot the same as a  regualar back self bow, but who would know,
if there is no difference in cast, that would be nice to know as well,,,,
if you can get a bow from what might not make a bow, even if the cast was not so great, that would still be a bennefit,,

thank you Jim we crossed post,, thanks for the input,,
I am understanding more and more,,

[DC]

I think it goes in the durability file. It's like making a questionable stave a little longer or leaving a knot a little wider. Little things that you hope will make the bow hang together a bit better. I know for a fact that with my variable release I would never see any dif with a chrono.
"Variable release", sounds like a good thing, doesn't it. Good sales pitch

[Wooden Spring]

"Variable release", sounds like a good thing, doesn't it. Good sales pitch

I call my "Variable Release" by another name... Usually it's "what the %$&# was that?" 

[bradsmith2010]

yes my release is a work in progress,, after 50 years still