BL compression fractures help

[Lee Lobbestael]

Hey guys. two years ago I cut and split five or six black locust staves. I let them cure for a year and attempted a long flat bow with one. It chrysalled badly so I scrapped it. Someone on here suggested that it may not have been dry enough or I tillered to fast. Well I attempted another over the last several months. I spent a month on tillering and stood near my wood stove between sessions.

Well I thought the tiller came out as close to perfect as I could get it but looking at the belly under a bright light just now I noticed that both limbs have tiny tiny compression fractures all up and down the belly. They are so small you have to be a few inches away and under a bright light to see them. And they are almost uniformly spread out over both limbs. They are so fine that a picture wouldn't show them. I cannot even feel them

My question is, Is this bow doomed or is it worth finishing?

[Badly Bent]

Lee I would go ahead and finish the bow. If they are the sort of micro compression fractures and are evenly spread out then the tiller may be just fine and the bow could survive a long, long time I believe. I have one similar to what you described that I've shot now for
a couple years without and further change in amount of chrysals or any change in tiller or draw weight, I'm confident enough in it now to even take it out strung all day hunting. I've made a half dozen from bl and all have survived and only one came out with none
of these tiny fractures. If your close to finished with your bow you may as well complete it and see what happens, can't do much about the fractures now that their there. Keep us posted, I'd like to know how it works out for you.
Greg

[George Tsoukalas]

When chrysals are spread out over the length of the limbs that is an indication that the design is not adequate for the draw length or weight wanted. Perhaps you could indicate your draw length, Lee. Also tell us about the length and width of the stave and the weight wanted. You could finish it but eventually the bow will fold up at one of those weak spots. Been there. Jawge

[Lee Lobbestael]

Thats the odd thing George I overbuilt it for that reason. It is sixty eight inches ntn inch and three quarter wide untill the last twelve inches and tapers to three eighths inch tips. Its about 55#@28"

[Badly Bent]

Lee, have you shot any arrows out of it yet? If so have more fractures revealed themselves? If not and your tillered out I would continue to shoot a couple hundred rounds and check along the way for changes.

[Lee Lobbestael]

I have shot about a dozen arrows through it. I noticed the fractures after that but they could have been there before I shot I just never looked at it under the light until this morning

[George Tsoukalas]

Lee, seems like you did the right thing. How big is the non bending handle section?

[Shaun]

A 3/4" wide bow is very narrow and usually made with a D cross section. This places extreme compression stress on the narrow belly. BL is known for its tendency to crysal in compression. A flatbow design with nearly flat belly would put much less stress in the compression zone near the surface of the belly by spreading it out over a larger area.

[steve b.]

1 3/4", shaun

[blackhawk]

Id like to see your tiller before making any comment as to why.....and how is the growth ring ratio in the stave? The best locust I've found is dark wood,and big ringed,and has a small early growth compared to the late wood....the locust with light colored wood with small rings and thick early growth to late growth seems much less dense and more prone to having issues....

[Lee Lobbestael]

Hey guys sorry I didn't have internet access for awhile. Yeah I meant 1 3/4" wide Shaun. I don't have a camera to get pics of it right now and I don't know if it is lighter or darker than average because it is the first BL tree I have cut. I hope this bow holds up because it shoots great and has almost no set so far.

[PEARL DRUMS]

Lots of fractures and not much set doesnt go hand in hand. Sumpin's fishy Lee. Maybe the wood is wet? It may have been cut years ago, but that doesnt mean its dry. Where was it kept prior to your build?

[Lee Lobbestael]

Yeah maybe it will take more set. It hasn't as of yet tho. Upstairs in a closet for several months and then by my wood stove as I was building it. I assumed the woodstove would dry it quick

[sleek]

I have made about 6 BL bows and none had these problems. I also heat treated the bellies on them very well, to the point of significant color change. I didn't do it quickly either, one bow took 2 hours to heat treat. I was shooting bows 50 lbs at 25 inches that were only 60 inches long and 1 1/4 inch wide with no problems. Try a good heat treat. Your tiller will change after it and it wont take much to fix it. Just brace the bow and scrape away until the tiller i even at brace and fine tune after that as normal.

[mikekeswick]

Black locust is a very stiff wood for it thickness.
It is very strong in tension but a little 'brash' in compression. Can't think of a better word...it's good in compression but almost too good in tension. A very good candidate for trapping and heat treating.
The fact that the chyrsals are small and evenly spread is a sign that the tiller is likely to be good and bending correctly - if it wasn't then then would be worse where it was bending too much. However the reason they are there is that you have asked the wood to bend too far for it's thickness. If the bow had been a little longer, or wider or lower draw weight then the limbs would have been a little thinner eg. able to safely bend further, and you may have got away without any.
Anyway yes I would finish it BUT only if the chrysals don't change after a few hundred shots. Maybe put some rawhide backing on and don't get too attatched to it.