Saturday, 19 August 2017

Messing with Bamboo

I've been reading around heat treating bamboo, and like a lot of stuff it's all rather confused and poorly defined with conclusions ranging from, it makes it worse, to it makes it better.
Well I have an off cut from my crossbow prod making which is planed to a nice flat one side with the outer surface intact on the other. So I cut this diagonally to make two tapered limbs I did some bend tests with the limbs up either way and messed with some heat treatment, but it was all rather inconclusive.
One problem I think is that simply  hanging a 2# weight on the tip wasn't giving enough bend to be significant. Anyhow here's the question:-
If you were to make a bamboo bow from one piece, would you have the back of the bow as the flat planed inner bamboo or the hard, shiny outer surface?
The received wisdom is that the strength of Bamboo is mostly in the outer fibres and that most materials like wood and bamboo are stronger in tension than compression. Now this would suggest that you's want the stronger side on the belly.
Of course I could just look at a Youtube video of how a Batak native guy makes a bamboo bow, but I do like to check out stuff for myself.

So, I glued and bound the two pieces together to form a bow flat faces meeting together for a few inches in the middle, made simple nocks by binding thread round the tip and letting low viscosity superglue soak in (V quick and effective). I put a string on and pulled it which immediately showed it as much stiffer in one limb than the other. The hard glossy outer bamboo to the belly was the stiffer limb. The preference for having it this way round is also shown by the fact that the other limb (glossy outer as the back of the bow) took a bit of set.
Now, here's the supplementary question for a bonus point:- How will the flat planed bamboo surface hold up as the back? Will it splinter at the nodes?
What is the point of all this?
Well if you have a bamboo slat and want to make a V quick simple boo bow maybe the counter-intuitive shiny side as the belly is the way to go.
Just in case you didn't watch the video, yup, that's the way he did it :-)

Still dunno if the heat treating made any difference... so many experiments, so little time, and the kitchen still isn't decorated. Slow and steady wins the day ;-)

2 comments:

  1. Nice experiment Del! I did some tests with boo a while ago. Took an old 40 lbs boo backed ipe pyramid, planed the belly flat and glued some boo on the belly. I prepped the boo exactly the same as I would have done with a backing. The boo added more than 30 lbs of draw weigth! I ended up with a 75@28 bow. The boo on the belly held up fine and I even broke my personal flight record with it.

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