Dumb question on "Belly side"

[AndyTurner]

Hi,

If we back a bow to prevent splinters lifting on the backside, which is under tension, then why don't we do the same thing for the belly of the bow where the wood fibres are under compression? Surely they are prone to some sort rupture as well?

Thank you for all input in advance! 

Andy

[BAfromPA]

There are plenty of examples of adding a belly lam to a bow. Sometimes to increase the weight or due to bad tillering causing frets. The most extreme examples are the horn bellied composite bows.

[AndyTurner]

There are plenty of examples of adding a belly lam to a bow. Sometimes to increase the weight or due to bad tillering causing frets. The most extreme examples are the horn bellied composite bows.

Hi. Thanks for response.
Hmmm but a belly lam like wood/horn/fiberglass etc would do work right, so therefore not there to "protect" the bow.

[PatM]

 The initial material is supposed to be able to do that.     A bow tends to be backed because the initial choice needs help.

[Marc St Louis]

Hi,

If we back a bow to prevent splinters lifting on the backside, which is under tension, then why don't we do the same thing for the belly of the bow where the wood fibres are under compression? Surely they are prone to some sort rupture as well?

Thank you for all input in advance! 

Andy

Only chrysals and that is due to over-stressing the wood.  For the wood to splinter on the belly the splinter would have to drive itself further into the wood

[AndyTurner]

Thanks Pat

Thanks Marc. Marc please can you explain, "Only chrysals and that is due to over-stressing the wood." - I have no idea!!!

[PatM]

Compression fractures where the wood cells get squeezed to failure. 

 I also think plate tectonic failures happen due to wood grain abruptly changing direction in the working limb.   Less of an issue with perfect tiller since marc is less concerned with this, but still we see it fairly often.

 

[mmattockx]

Thanks Marc. Marc please can you explain, "Only chrysals and that is due to over-stressing the wood." - I have no idea!!!

What Marc means is that belly wood only fails in compression, which forms chrysals. Only tension will lift splinters so the belly wood never fails that way and it is not a concern on the belly.


Mark

[bownarra]

Because there is no need and no.
Just go and bend some wood

[AndyTurner]

Because there is no need and no.
Just go and bend some wood

attached!

[AndyTurner]

Thanks Marc. Marc please can you explain, "Only chrysals and that is due to over-stressing the wood." - I have no idea!!!

What Marc means is that belly wood only fails in compression, which forms chrysals. Only tension will lift splinters so the belly wood never fails that way and it is not a concern on the belly.


Mark

Ok so what are chrysais?

[PatM]

Visible compression damage usually in the form of lines that look like slightly diagonal or across the belly scratches.

[mmattockx]

Ok so what are chrysais?

As PatM says, they are compression fractures on the surface of the belly wood. This pic shows a very badly chrysaled bow:




Mark

[AndyTurner]

Ok so what are chrysais?

As PatM says, they are compression fractures on the surface of the belly wood. This pic shows a very badly chrysaled bow:



Mark

Hi Mark, sorry but I can't see the pic.

[mmattockx]

Hi Mark, sorry but I can't see the pic.

Some days the interwebs aren't all they are cracked up to be... Let's try this one:




Mark