Compression fractures

[LaBill67]

I have completed several bows since starting this new endeavor of bow building and many have developed compression fractures. The bows with the compression fractures are: a red oak pyramid bow with a fiberglass cloth backing, a maple, purple heart, white oak belly tri lam, a white oak backed purple heart no backing, a maple backed purple heart with burlap backing over the maple, w ell you get the idea I hope.  In each case the tiller was reasonable and the weight was about 40-45#.  I don't know if it is me or the wood.  I currently am shooting a IPE backed with pecan that is 65 1/2" NTN in a pyramid style that weighs in at 65#.  I am hoping it holds up even though it is  a bit too heavy for me.  If anyone has any thoughts on this subject by all means let me hear from you.  I'm thinking of trying a mid weight, 40-45#, pecan IPE flat bow for my next attempt. Just needed to vent a bit I guess.

[PatM]

Your belly wood choices are too fickle when combined with your backing choices.
 Try Maple backed Ipe if you want to  narrow your chrysals down to being only because of poor tiller.

[Badger]

    Start off with better wood choices. Purple heart is not a true bow wood even though you will find several examples of good shooting purple heart bows. It is prone to chrysaling. Maple is somewhat prone to chysaling and will not usually tolerate tight bending areas. same with red and white oak. Both maple and red oak will make good backings if straight grained.

[LaBill67]

Thanks guys for your insight.

[Pat B]

I agree with Pat and Steve.

[wizardgoat]

Would be good if we could see some of these bows, we could tell you if your tillering is also a reason

[bradsmith2010]

agree with above,,
what about making a self bow,,

[bushboy]

The only thing purple heart has going is the look witch dulls over time!non bow In my opinion!super hard and low compression strenght!red oak is better but not by much.find some hickory,elm,or hophornbeam.

[scp]

Wood is stronger in tension than compression. I routinely "trap" the back when the working limbs are not as wide as 1&3/4 or 2 inches but thick enough. Some early experts definitely recommended rectangular cross section, but I'm not sure it still holds universally even for flat self-bows.

[bradsmith2010]

scp, good point, I am not sure about any rule of thumb that holds universally,, 

[Badger]

      I never have got into trapping and wouldn't know how to measure its effectiveness. I would imagine a crowned back is the same as trapping. I have never had a problem using staves with moderate crowns. Possibly wood is better designed to bend with a crowned or trapped back.

[bradsmith2010]

I guess a start would be to test some trapped back bows for performance,,
to see if there is any difference compared to a regualar bow,,  i dont know, I have never done it either,, but have never had a problem crushing the belly with the woods I use,, mostly osage,, maybe on some woods it is very benificial,,

[Marc St Louis]

I've found that tension strong wood like Elm perform better when they have a crowned back