Bow breaking without warning
Hi,
I would like to get your advice, where is the mistake:
After many readings of ''traditional Bowyer Bible vol 1 to 3, ''Arc 4'' by Jean Claude Buisson, I decided to try. I took the Moshcheveya Balka bow dimensions , i made a sandwich with with 2 ash strip of 1/8 inch thick (3.2mm), 2 inches wide (50 mm) and 47 inches long (1170 mm) with a 9 oz (300 g/square meter) fibreglass layer between the 2 strip and 1 3/8 inches (35 mm) wide ash handle. On each end, I glued a 7.5 inches (18 cm) long by 1 3/8 inches (35mm) wide black walnut (41 degree from arm). I laminated (on back and belly) a 9 oz (300 g/ square meter) fibreglass. I used a G5 epoxy with a pot life of 90 minutes. The bow was left to dry for a week. I trimmed the excess fibreglass.
On the tiller stick: 10 tractions to 8 inches (200mm) and I got 20 lbs on the balance. 10 others tractions at 9, 10 and 11 inches and so on. At 12 inches, I got 30 lbs and 35 lbs at 16 inches. Everything seem to be ok (that is what I thought!!) because I aimed 50-60 lbs at 28 inches. But at 18 inches, one arm broke without warning at the end of the fadeout.
On the autopsy, I saw little raised dots on belly side (on the unbroken fadeout). These dots form a line from one side the other. On the pictures, you will easily see it.
Where is the problem and why, please explain.
Wolverine
I would like to get your advice, where is the mistake:
After many readings of ''traditional Bowyer Bible vol 1 to 3, ''Arc 4'' by Jean Claude Buisson, I decided to try. I took the Moshcheveya Balka bow dimensions , i made a sandwich with with 2 ash strip of 1/8 inch thick (3.2mm), 2 inches wide (50 mm) and 47 inches long (1170 mm) with a 9 oz (300 g/square meter) fibreglass layer between the 2 strip and 1 3/8 inches (35 mm) wide ash handle. On each end, I glued a 7.5 inches (18 cm) long by 1 3/8 inches (35mm) wide black walnut (41 degree from arm). I laminated (on back and belly) a 9 oz (300 g/ square meter) fibreglass. I used a G5 epoxy with a pot life of 90 minutes. The bow was left to dry for a week. I trimmed the excess fibreglass.
On the tiller stick: 10 tractions to 8 inches (200mm) and I got 20 lbs on the balance. 10 others tractions at 9, 10 and 11 inches and so on. At 12 inches, I got 30 lbs and 35 lbs at 16 inches. Everything seem to be ok (that is what I thought!!) because I aimed 50-60 lbs at 28 inches. But at 18 inches, one arm broke without warning at the end of the fadeout.
On the autopsy, I saw little raised dots on belly side (on the unbroken fadeout). These dots form a line from one side the other. On the pictures, you will easily see it.
Where is the problem and why, please explain.
Wolverine
Was the glass fibre unidirectional or the woven cloth type? If it was the woven cloth type that would explain the breakage as it invariably fails where the weave runs at right angles to the limb (at least, this has been my experience with experimenting with various glass fibre enforced designs). From the picture, it looks like the weave has delaminated, hence the little dots.
For bow construction, unidirectional glass is required.
Regards,
Dylan
For bow construction, unidirectional glass is required.
Regards,
Dylan
First at all, are you sure asket right people ? We know litlle about natural composites , but this disain vith epoxi , plyester materials...?!
Yes Dylan, it was the woven cloth type.
Do you know a good company to get unidirectionnal fiberglass because, here in Canada, i didn't find any.
Thanks
wolverine
Do you know a good company to get unidirectionnal fiberglass because, here in Canada, i didn't find any.
Thanks
wolverine
Most unidirectional GF comes in prelaminated strips specifically for bow making. I think they?re produced by Gordon Composites. Unidirectional tape can be used but it?s still a pain as you have to tease out the connecting fibre holding it together. This has to be removed once the tape is ?wetted out? with resin on the bow before hardening. If you take the fibre out before this the tape just falls apart, if you leave it in you have the same problem as the cloth with fibres running at right angles to the limbs.
I have heard of people using fibreglass string (tor?) and laying it down in parallel lengths like sinew.
I?ve used East Coast Fibreglass in the UK before. But I suspect the cost of shipping might be prohibitive.
I have heard of people using fibreglass string (tor?) and laying it down in parallel lengths like sinew.
I?ve used East Coast Fibreglass in the UK before. But I suspect the cost of shipping might be prohibitive.
Contact rodney wright he is a bowyer who makes fglass composites and is based in Quebec,I believe he supplies unidirectional fglass and supplies in canada.He's the chap that makes the firehawk.
I've also tried to make such a laminated bow and it's nomal that breaking goes trough the limb, over and under the handle. It's a big concentration of force in this place. The part next to the handle must be the thickest part of the limb.
Thanks everybody
Wolverine
Wolverine