Sunday, 18 January 2015


The Primitive exploded on the tiller. Damn!
Not a very auspicious start to the year.
I'd been cleaning up the lower limb and it was now bending a bit more, I'd been flexing it and thinking I need to ease off the upper limb to match, but I'll just pull it to 50#.
It had been there before... but it went Bang (at about 26")
I've highlighted the two breaks in red.

It would be easy to look at the back and say oooh there are lots of ring violations, that's the problem, but I think that's over simplistic.

There were plenty of knots and bumps on the lower limb, maybe the outer 1/3 wasn't moving enough. Maybe the sapwood had got too hot during heat treating? I don't know.
BUT, there is plenty of thickness of sapwood there.
Looking closely at the pics, you'd think the bow would be supple and durable with that much sapwood and so little heart.
The more I look at it, I think the break probably started at a point where the limb was slightly thin (between two bumps) and it narrowed slightly there. maybe leaving extra width and thickness at a knot merely creates a weak point adjacent to it!
Some scant consolation, I've just noticed a faint pencilled L  (for LEAVE) across the break at the thin point, I'd obviously spotted it was a whisker thin there. (Lower left pic)

The darker picture shows the back of the upper limb with fewer bumps and knots and  more even sapwood contours.

Pic left shows how the sapwood flows around the pegged knot, note the sapwood din't actually snap at that point.

Maybe the bow was just a tad short for that draw weight.
Anyhow, the lower limb fractured at two places both near knots/bumps. If I had to fault myself, I'd say I should have reduced the right limb to match as soon as I felt the left was flexing too hard. Mind, it was very subtle, it's not as if it was a huge clearly visible overbend.

To further the investigation I sawed a cross section from between the breaks... it looks great!

It's just a damn shame as it was going to be a V pretty bow.
On the plus side, I had been thinking of putting longbow style horn nocks on it, and at least I hadn't spent the time doing that!

Once more to the old question... How long does it take to make a bow? Maybe you need to factor in the ones that don't make it.
Just as well I enjoy makin' 'em.
Damn, damn and thrice damn.

No comments:

Post a Comment