Trapping

[DC]

Mark, we were typing at the same time and you won.
 What is the advantage of a bow that's "balanced" in tension/compression? Is it just less mass?

[mmattockx]

What is the advantage of a bow that's "balanced" in tension/compression? Is it just less mass?

Perfectly balanced would mean both sides are being used to their maximum capacity, so there is no excess material sitting around not being utilized. That should give you the lightest bow for any given draw weight, given the same design.


Mark

[bradsmith2010]

ok could you shoot the untrapped bow throught the chronograph,,
now trap it, and shoot with appropriate 10 gpp arrow,, and see if it helped the speed of the bow,,

[DC]

I've been thinking of that. I just have to pick a bow to lose a pound or two. When I trapped this one I checked the DW before and after. I think it lost 2#. I was surprised how much wood I took off and how little the DW was effected. A person could really learn a lot it they videoed everything. Especially if they have a memory like mine.

Bownarra, in another post way back you suggested I trap the bow. Thank you for that. You also suggested that I not trap the recurves. Why?

[bradsmith2010]

since it would reduce stress, could you cut it a bit shorter to gain back the 2# then test

[willie]

ok could you shoot the untrapped bow throught the chronograph,,
now trap it, and shoot with appropriate 10 gpp arrow,, and see if it helped the speed of the bow,,

Brad, a number of reasons come to mind that might make your results inconclusive.
 1. any gains noted might have come from from lightening the limb. some designs will show more benefits from limb lightening than others, so you would have to know more what ifs about your particular design.  In a related idea, if you hope to learn from 10gpp arrows, what might make improvements for 5gpp arrows (which is what I think DC is trying design for), then the test will be less conclusive.
2. As Mark pointed out in the second post, If the belly is strained by shooting the first test before trapping and then the bow is trapped and the strain distribution is changed, it would be like making the second test with an over drawn bow.

[bradsmith2010]

good point,,very interesting for sure,,so if the bow did shoot faster it might be simply from reducing the mass weight,, for the given draw,,???

[willie]

I'm not sure if you could ever get equal deflection on the two sides because tension doesn't seem to produce any set while compression always seems to.

I have seen this idea presented often in discussions, and I think it is also made in the bowers bible.
I can easily imagine an example of the "bow split lengthwise" test where the belly has taken set but the back hasnt. To me, this indicates the yield point, or that point where elastic behavior ends and plastic behavior begins, or simply set taking happens, is different for tension and compression. To conclude the test proves wood does not take set in tension would be premature, and I have always been a bit dubious of the assertion based on some observations of wood failures.

Short of inventing a procedure for a new test to be included in the wood database that will never happen..... I would be interested to hear from other bow makers of any experiences or even suspicions.

[bradsmith2010]

I had a sinew bow that was shot in quite well,, the sinew came off,,
the belly had not taken any set, and the wood part went back to its original profile before sinewing,,

[DC]

good point,,very interesting for sure,,so if the bow did shoot faster it might be simply from reducing the mass weight,, for the given draw,,???

I think that's where the gain come in. In more than just trapping. Just about everything we do is to equalise stress so we can use less wood so the limb can return faster. It's an old drag racing thing--add lightness. I think that's all there is to it until you start to think about limb flexing and all that stuff.

[willie]

I had a sinew bow that was shot in quite well,, the sinew came off,,
the belly had not taken any set, and the wood part went back to its original profile before sinewing,,

sounds like the sinew enabled you to archive your design goal without overstraining the wood. I think steve (badger) often comments about how he has come to prefer bows with less and less set, both observable set and the overstressing that precedes the observable.

Did you put that bow back into service?

[Selfbowman]

good point,,very interesting for sure,,so if the bow did shoot faster it might be simply from reducing the mass weight,, for the given draw,,???

This is what I think happens. Arvin

[DC]

  In a related idea, if you hope to learn from 10gpp arrows, what might make improvements for 5gpp arrows (which is what I think DC is trying design for), then the test will be less conclusive.

I have no idea how to design for lighter arrows. Or heavier arrows for that matter. I don't know what the difference would be.

[willie]

if your designs are "trIal and error"  method, then test with arrows like will be used at the tournament.

[MM2]

Greetings, great and glorious Bowyers!

I'd like to join with a question: can I trap a quartersawn board bow?

Thank's in advance!

Michael