Trapping

[willie]

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

quartersawn might be a +
what kind of wood? is it a selfbow?

[mmattockx]

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

Why wouldn't you be able to?


Mark

[DC]

You always can, the question is should you. I'm leaning toward probably if you have good wood.

[MM2]

Greetings, everyone!

Willie: Right now, it's just a plan. I have some ash billet, and as they are only 32 inch long, my plan is a take down bow. (As far as I know, the ash is very strong in tension, but not so strong in compression).

Mmattockx: I'm afraid the limb will be very weak near the edge.

DC: The wood is very good. 

Have a nice day! (Or night, if you live on the other side of the globe.  )

Michael

[mmattockx]

Mmattockx: I'm afraid the limb will be very weak near the edge.

Don't make the belly edges sharp, leave some thickness there. Make it like the one on the right, not the left.


Mark

[Selfbowman]

Question.. If let’s say white ash is 30% weaker in compression versus tension can you reduce the back by 15 percent  on each side to even out the stress. Question two . What’s the difference in percentages on white ash? I have a good white ash stave. Arvin

[mmattockx]

Question.. If let’s say white ash is 30% weaker in compression versus tension can you reduce the back by 15 percent  on each side to even out the stress. Question two . What’s the difference in percentages on white ash? I have a good white ash stave. Arvin

1) It doesn't work that way, you have to shift the neutral axis by 15% (1/2 of the 30% difference) of the limb thickness to even out the relative strains. That assumes the MOE is the same in both tension and compression directions, which seems to be very uncertain based on information that has been posted as of late.

2) I have no idea. Without lab quality testing equipment you will likely not be able to measure it accurately, either. Have you tried doing a bend test or two with a piece cut off the stave?


Mark

[willie]

I was writing as Mark posted, but will add

Basically, trapping is limited by  how narrow do you dare to go without back explosions? some testing of short trapped slats bent around something like the rim of a 55 gal drum could be done to give a practical  idea of the proportions that might work. bending around a form means you could take rippings straight off the able saw to test

 a few things to keep in mind though,

any imperfection in the narrowed back is going to be magnified compared to the same imperfection in a wider back, so clear sound straight grain etc.is best.

keeping the trapped back flat and with a smooth radius at the corners is more important than with a wider back

if the back is at its optimum dryness, having it drier may be a mistake. this may be a bit different from what the belly considers optimum

[MM2]

Dear Mark and Willie!

Thank you for your advice!
Presently I'm working on another bow, but I'll try the thing later.

Bye!

Michael