I have finished 1 red oak board bow that is backed with 3 layers of fiberglass sheetrock tape bedded in Titebond 3 glue. I have shot it numerous times in the last 4 months. Yesterday about 6" of the top limb broke off while shooting. The break was straight across with the backing breaking at the same place. I could not detect any defect at the break that would have caused it. Today while tillering my second bow, which is also backed with fg tape, I had reached 14" of draw and 6" of the tip broke off. The break looked identical to the one on the first bow and again didn't evidence any defest at the break.
I would not have thought the backing would have failed this way.
I tillered the bows such that the tips don't bend in the last 6" but I am careful to have a smooth transition at this point.
I tested the moisture with a cheap moisture meter that I don't know the accuracy of. It showed 12%
I would appreciate any comments from your experience that would help me to understand what happened and what I can do to avoid this in the future.
That does sound like an unusual place for two breaks.
Pictures of the area would mean a lot. Very difficult by describing only.
Even three layers of FG tape won't stop a bad break mostly for splinters etc.
If you can a 1/8 backing of hickory etc. would be tougher.
Feel your pain.
Ron
my guess is you are crushing the belly with the sheet rock tape/glue backing. red oak doesn't do well with a heavy backing, and it broke in that spot because that is the thinnest the oak is in the last spot it bends before the non-bending tips. just my guess.
My first red oak board bow broke in a similar fashion. I had also put three layers of fg tape with titebond. Afterward I found some literature that indicated exactly what has been suggested here.
Stan
just because its fiberglass doesn't mean its not going to break...its actually quite weak. Its just sheet rock tape.
If you get fiberglass cloth than it will be much stronger.
I've only had one red oak bow break and I have never backed any of them. The only one that broke was because it was a overstrained design.
If the grain is straight with no little pin knots than it shouldn't break if well tillered.
Is the grain running full length?
Got any tiller pics? That will probably tell the story, if the board was good grained to start with.
The Red Oak Bow backed with Linen have Broken on Me!! :mad: :knothead: :biglaugh:
My first red oak bow backed with the fg tape broke because I allowed a neighbor to look it over. He of course drew the bow... Yep, there was a little "crack" sound.
My second red oak bow folded very slowly after I put a home-made hickory backing on it. I was experimenting.
Stan
It's hard to tell without seeing pictures. Could have been poor grain orientation, an internal wood flaw, etc. However, the 3-ply tape backing was probably the culprit. I doubt very much it overpowered the belly (although that's certainly a possibility). Three layers is excessive and would create a false backing that takes a bigger chunk of the working load than FG tape can handle. I believe as a result the backing simply gave way, which led to a compromise in the bow limb at that point.
I am wanting to build a red oak board bow with same backing. I already have the materials. Will see how it goes. Floyd good luck on your next one.