Ozbow

Well it finally happened and it's got me stumped, the glue didn't fail, the Tasi Blackwood lamination failed in spectacular fashion, it split almost perfectly through the center of a 30 thou parallel lam so straightness of grain certainly wasn't the problem. The young fella that owns it said he had just put about 200 arrows through it that day and when he lifted it (with stringer fitted) to unstring it it made a cracking sound and did this.
As you can see there is a good layer of timber on both sides of the offending split.

Has anyone else had or seen a similar failure?

It goes with out saying the limb will be replaced, luckily I still have one lamination left of the really dark Tasi Blackwood that is on the back of the limb.

Cheers Rob.

Hey Rob, just a thought as never scene that before especially in the centre of the Lam. Wouldn't use a wood harvested from Tassie in the tropics those southern trees just havnt been through a heated 40 deg hunt before. Just a thought.

Cheers Wayno

Maybe the young bloke dry fired a few times.........

I have seen that happen with other woods Rob. Why does it happen?

Perhaps there was an unseen fault in the wood.

If you haven't used that wood in your bows before perhaps it can't stand the sheering forces created in a bow limb.

Jeff

Hey Wayno how would ya be? well it's called 'Tassi blackwood' but it grows right up the east coast and was sourced localy so I don't reckon that's it. Besides it lives In Mount Gambia.

Rod,, Dry fired ,,, maybe but you would expect the limb to split the other way from string impact.

I've used Blackwood in several bows Jeff and always found it a very suitable timber for the job, never had a problem with it.

Sure looks like shear forces at play, Rob but as to why, that is the question I wouldn't be able to answer.

Maybe he dropped it out of a plane and it landed on that limb sideways....

Just out of curiosity, would the location of the split be at the neutral plane? That is, at half of the depth of the limb?

Yo, Yeoman, no the split is around 15-20 thou from the belly glass and about 80-90 thou from the glass on the back of the limb.

In fact the split is so uniform and tidy I decided to remove the nock tip reglue the split and pop it back into the form and it's come out looking quite good. I'll make a new nock tip, put the limb back on the bow, string it up and put a couple of hundred arrows through it and see what happens. I reckon it will be fine.

Rob.

Flatliner wrote: it split almost perfectly through the center of a 30 thou parallel lam so straightness of grain certainly wasn't the problem......

Flatliner wrote:, no the split is around 15-20 thou from the belly glass and about 80-90 thou from the glass on the back of the limb.

I am a little confused with the above are there multiple core laminations? 30 thou is about one and a half times the thickness of the cardboard used in a corn flakes box.

Daryl.

greybeard wrote:I am a little confused with the above are there multiple core laminations? 30 thou is about one and a half times the thickness of the cardboard used in a corn flakes box.

Yeah Daryl there are three core laminations, the one on the back of the limb is a 1"/.001" wood taper that opposes the central 1"/.001" bamboo taper and the belly lam is a 30 thou parallel lam which has split pretty much through the center leaving around 15-20 thou of timber stuck to the belly glass.

Rob.