Banksia bow failure

Message

Muz1970 · #1 Post by **Muz1970** » Wed Dec 23, 2015 12:41 pm

Cut the window in yesterday morning before work and left it strung. Came home to find the Jarrah in riser had split. Wasn't a happy camper. Put one coat on the Banksia to show you guys the grain. Used Woody Pear and Banksia veneers, the woody pear is really dark under the glass. Don't think I'd waist it on veneers again.

Time to start again

: 20151222_172538_resized-2.jpg (118.35 KiB) Viewed 5351 times

: 20151222_172955_resized-2.jpg (114.7 KiB) Viewed 5351 times

: 20151222_173225_resized-2.jpg (94.75 KiB) Viewed 5351 times

: 20151222_173244_resized-2.jpg (85.8 KiB) Viewed 5351 times

Muz1970 · #2 Post by **Muz1970** » Wed Dec 23, 2015 1:02 pm

: 20151222_172705_resized-3.jpg (87.78 KiB) Viewed 5345 times

This shows the split a bit better

bigbob · #3 Post by **bigbob** » Wed Dec 23, 2015 1:34 pm

Bugger! Was the jarrah well seasoned? The Banksia looks quite a bit like beefwood.Never seen a split like that before, have seen some going with the horizontal plane , stress cracks or whatever but never one like that!

Muz1970 · #4 Post by **Muz1970** » Wed Dec 23, 2015 2:15 pm

The Jarrah is recycled floor boards. Been in my shed for 10 years. Came from someones house once. Probably 25 years dry minimum.

Gringa Bows · #5 Post by **Gringa Bows** » Wed Dec 23, 2015 6:10 pm

Wow,its not a glue line failure,looks like its cut a fair bit past centre ay mate,and started cracking in the corner of the shelf .......havent seen one crack like that ,well not a glass bow.....Bugger

bigbob · #6 Post by **bigbob** » Wed Dec 23, 2015 8:07 pm

i never picked up on that Rod, but you're right. That is just what it looks like, emanating from the corner of the shelf. Fancy splitting the glass too.

Alex · #7 Post by **Alex** » Wed Dec 23, 2015 9:39 pm

Did you glued the riser with epoxy ?
And how heavy (poundage) was this bow ?
Haven't see this happen , never , not this way...
Alex.

Muz1970 · #8 Post by **Muz1970** » Thu Dec 24, 2015 7:55 am

I use smooth on glue. The glue join didn't fail. The bow was 74#@28". 89# at my 31" draw. Rod and Bob are correct in that it appears to have started in the corner of the shelf. At the time of failure it was at rest on the work bench while strung. Put it down to a bad piece of timber I think.

Hamish · #9 Post by **Hamish** » Thu Dec 24, 2015 9:50 am

How wide was the arrow pass? It looks way too narrow especially for the strength of the bow.

Muz1970 · #10 Post by **Muz1970** » Thu Dec 24, 2015 10:10 am

2 inchs.

perry · #11 Post by **perry** » Thu Dec 24, 2015 8:51 pm

Wow, Yeah never seen anything like this before but I gotta Wonder it looks like a Torque induced Fracture gotta Wonder if that Top Limb was Twisting ???

regards Perry

Gringa Bows · #12 Post by **Gringa Bows** » Thu Dec 24, 2015 9:31 pm

Did you use UL or ULS glass mate ?

bigbob · #13 Post by **bigbob** » Fri Dec 25, 2015 8:41 am

perry wrote:Wow, Yeah never seen anything like this before but I gotta Wonder it looks like a Torque induced Fracture gotta Wonder if that Top Limb was Twisting ???

regards Perry

they were my thoughts too Perry as stress will induce where ever there is an intersection of two planes and usually in cases like this, a radiused corner at the intersection of said planes will alleviate some of this stress. Twisting of one or both limbs would concentrate stress at point of least resistance, and result in a torquing or twisting force to cause similar result to this.I see there was a radius at the shelf.

Muz1970 · #14 Post by **Muz1970** » Fri Dec 25, 2015 10:20 pm

Righto...starting to make more sense now.

The bow was over targeted weight so i had reduced the limb width from fades right through to the tips. It was at the point if I went any further i thought I'd lose stability at the tips. As i had to make a few adjustments to correct some minor twisting. I had drawn the bow 6 or so times and was happy with it and left it on bench. Guessing now i may have gone to far with Perry's theory.

Thanks for the insight gentlemem....

Muz1970 · #15 Post by **Muz1970** » Sat Dec 26, 2015 11:38 am

Have only used UL glass so far Rod.

Anyway the next attempt is in oven this morning. All Sheoak veneers and solid Sheoak riser. Fingers crossed it comes out close to right weight.

More lessons learnt the hardway.

Muz

bigbob · #16 Post by **bigbob** » Sat Dec 26, 2015 12:04 pm

re the weight reduction, Muz, if it is not a large weight reduction, 'trapping' the limb edges [ radiusing the edges] is a quick way of bringing it down few pounds, as well as some judicial sanding of the limbs surfaces, taking care to remove equal amounts from each limb. These procedures are far more preferable than reducing width, which has as a by product, the tendency toward inducing instability in the limbs. I have dropped an easy 5#-6# by these methods.

Muz1970 · #17 Post by **Muz1970** » Sat Dec 26, 2015 12:10 pm

Did that as well Bob. Think I dropped it about 20lbs.

Once I've done a couple more bows I'll have a better projection of weights to go by. But these are valuable lessons learnt and hopefully not repeated.

Muz

Ozbow

Banksia bow failure

Banksia bow failure

Re: Banksia bow failure

Re: Banksia bow failure

Re: Banksia bow failure

Re: Banksia bow failure

Re: Banksia bow failure

Re: Banksia bow failure

Re: Banksia bow failure

Re: Banksia bow failure

Re: Banksia bow failure

Re: Banksia bow failure

Re: Banksia bow failure

Re: Banksia bow failure

Re: Banksia bow failure

Re: Banksia bow failure

Re: Banksia bow failure

Re: Banksia bow failure