Trapping

[williwaw]

I'm going to take the path of more compression resistant material in the belly.  Starting with thicker glass.....If I can get to no string follow and no, or very little,  loss of draw weight I'll feel that balance has been reached.

your choice of working the back harder seems very reasonable if consideration of the underlying core properties is called for. Maple (if similar to other hardwoods) is said to be twice as strong in tension than in compression. whether it can stretch as much as the glass above is doubtful, but it will be harder to stretch, being in tension.

when sinew is applied to the back of a bow, it is sometimes mounded up so  the outermost layer can stretch even more. Perhaps you could consider applying the extra glass you propose for the belly in a similar fashion, rather than spreading it across the full width.

[monterey]

An interesting thought.  One variable at a time of course.  That might be a fine tuning factor.

[mmattockx]

I'm going to take the path of more compression resistant material in the belly.  Starting with thicker glass.

I once asked an experienced FG bowyer about using thinner glass on the back in order to raise the stresses on the back and use more of its capacity (FG bows normally don't use anywhere near the full capacity of the glass). He warned me against going too far with that as the wood core tends to fail in shear right at the glue line if you work the FG lams too hard. The problem is the FG can withstand strains that are 2-2.5x higher than the wood can.

Using thicker belly glass is OK, but you can't go too far with making the back lam thinner when building an asymmetrical limb stack.

One approach to knowing what is happening is looking for deflex (string follow).  My bows are primarily ASLs which makes string follow easier to observe and more likely due to the higher ratio of core lams.

How much set do you see happen with your bows? A thicker FG belly lam might be a very good idea if the core is taking set that is measurable. It would shift the neutral axis and lower the strains on the core wood at the glue line to the belly lam.
 

What if there is no follow observed over time?  Then an indicator would be the changes in draw weight over time.  It calls for careful record keeping.  If I can get to no string follow and no, or very little,  loss of draw weight I'll feel that balance has been reached.

I agree, set shows up first in loss of draw weight (when tillering a wood bow, which is all my experience). That seems to be a very good way to detect it before it becomes visible.

I understand what you mean about being balanced now. You are trying for a no set bow in the end, which is a very worthwhile target.

Maple (if similar to other hardwoods) is said to be twice as strong in tension than in compression. whether it can stretch as much as the glass above is doubtful,

I use maple boards for bows and it definitely is twice as strong in tension as compression. No wood can survive the strains that FG can.

when sinew is applied to the back of a bow, it is sometimes mounded up so  the outermost layer can stretch even more. Perhaps you could consider applying the extra glass you propose for the belly in a similar fashion, rather than spreading it across the full width.

Since FG is heavy this would probably not be the most efficient way to use it. I suspect you would get the same effect with a thinner lam that runs the full width of the belly and has less weight overall. Would have to crunch numbers to see how it all works out, though.


Mark

[williwaw]

when sinew is applied to the back of a bow, it is sometimes mounded up so  the outermost layer can stretch even more. Perhaps you could consider applying the extra glass you propose for the belly in a similar fashion, rather than spreading it across the full width.

Since FG is heavy this would probably not be the most efficient way to use it. I suspect you would get the same effect with a thinner lam that runs the full width of the belly and has less weight overall. Would have to crunch numbers to see how it all works out, though.


Mark

well maybe not mounded up as much as is done sometimes with sinew, but perhaps a thicker glass finished out with a crown?  I agree the performance might not be all that much different no matter how the glass is arranged, as it is so thin.

Perhaps I should clarify the context with which I tossed that idea into the discussion. I have drifted a bit from the OP's question about trapping for performance gain, and presume the ASL style Monterey is primarily building is designed with different goals in mind.

The problem is the FG can withstand strains that are 2-2.5x higher than the wood can.

Good Point. I am not sure if FG is too stiff to be used effectively with some designs if it cannot be strained to its full potential. Maybe something with half it's stiffness (but still  stiffer than the core) would be a useful laminate. One of the benefits FG brings to the table is its uniformity for use as a back or belly, reliving the bowyer from the need to find pristine wood with suitable grain orientation for the back if building without FG.  A thicker FG replacement would allow more "shaping" of the bow limb to emulate classic wood designs.

Admittedly, I am spouting off a bit with some untested theory about FG, but coming from a wood background, mixing and matching of materiel's of different qualities is more easily done.

I would be interested to hear of any results or view  links someone can post, that demonstrate what happens when thicker limbs are shaped more rounded such that the outer FG lams are reduced in width.
 


 

[Flem]

Like this?

Or this?

Check out what has been said in reviews about Schulz or Sunset hill longbows. Sorry I don't have any links, but info should be easy to search for.

[williwaw]

Thanks Flem,

I found lots of pics, but not many that can give a true sense of how round the limb might be getting.

I suppose my question was seeking comment on what happens when the rounding of the corners is taken to the extreme., ie approaching an elb cross section.

[mmattockx]

well maybe not mounded up as much as is done sometimes with sinew, but perhaps a thicker glass finished out with a crown?  I agree the performance might not be all that much different no matter how the glass is arranged, as it is so thin.

The problem with crowning is that it strains the material more in the high part of the crown and less in the rest. To use FG most effectively you want to strain all of it the same amount.

Good Point. I am not sure if FG is too stiff to be used effectively with some designs if it cannot be strained to its full potential.

It is never used to its full potential in a traditional bow. Usually it is stressed to no more than about 50% of its limits (often much less than that) because the core can't withstand much more or you run into stability problems with narrow and/or thin limbs. If you want to see what FG can do, look at current compound bows or compound crossbows. Thick, stubby limbs that generate enormous forces (and energy storage) with very small deflections. That is what a more optimal FG limb design looks and performs like.

Maybe something with half it's stiffness (but still  stiffer than the core) would be a useful laminate.

Yes! A lam or backing material that was closer in stiffness to wood but still significantly stronger in terms of the maximum strain it could withstand would be a great step forward. It would be somewhat of a holy grail of traditional bow material.

I would be interested to hear of any results or view  links someone can post, that demonstrate what happens when thicker limbs are shaped more rounded such that the outer FG lams are reduced in width.

A high crown acts the same as trapping in its effects. It shifts the neutral axis away from the crown, raising stresses on the crown side and lowering them on the opposite side.


Mark