Backwards Pyramid Bow

[GregB]

Good looking bow, but I can't get over how it looks like it's strung backwards! As already said, you'll have to keep us posted to see how it's doing after a lot of shooting time. Congrats on accomplishing this design successfully!

[GraemeK]

Thanks Greg

I think it should be fine in the long run, the only thing I think might happen is it may take set with a lot of use  -- Graeme

[Hillbilly]

That's awesome, never woulda thunk it.

[GraemeK]

Hi Hillbilly
It just goes to show you that a lot of what we think of as fact and set in stone is just our way of making the world seem safe and predictable.

I think of it like my experience with limb tips -- over time I have made them smaller and smaller and and now they seem to be scary small and I think it is just not possible to make them any smaller but the fact is that I have never had one break so so they must still be strong enough but I just can not bring my self to make them thinner than about 4mm wide.

Graeme

[jkekoni]

It is not a backwards bow. It is bamboo belly bow.

Bamboo skin as belly is not a new idea. It has been used as sinew backed in horn bow substitute, where hornbows have been norm. It has also used as self bows in Bhutan.

I think Osage should be ALSO strong enough to work well as backed with bamboo.


(I'll add some links.)


I would reinforce the fades by wrapping with linnen and wood glue, I see potenttial for splintter in the area.

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Asian hornbow like bows made with bamboo belly.
http://www.atarn.org/FAQ/bamboo_composite.htm
http://atarn.net/phpBB2/viewtopic.php?t=123&highlight=bamboo+belly
http://www.hornbow.com/mokgoong.html

I could not find article about Bhutanese
bamboo selfbow made from 2 pices and joined at handle.

[a finnish native]

I think the point here was to try something new for the bow maker him self. Still, a really nice bow.

[Pat B]

Graeme, this is an interesting idea and interesting looking bow. Osage is definitely strong enough to be a backing and bamboo will work for the belly. One way to increase the compression strength of the boo, and allow for less set is by tempering the boo before glue up. I watched James Parker temper boo for one of his short, highly stressed recurve bows and you would have thought it was toast when he was done.
    Experimentation is what keep primitive archery alive. It always has. Nice work.    Pat

[PeteC]

That's a great lookin' bow,and it sounds like it's performing well.I hope it'll keep sound for you. Good work.  God Bless

[GraemeK]

Hi Pat
I have seen boo heat treated to increase the compression strength and it seems to work well but I have been skeptical about how the heat effects the bow over its working life -- obviously it makes the cells harder and more brittle so I can not help but wonder it they break down with lots of use. I guess I am going to try it if i make an all boo bow but with the current osage / boo bow it has not taken any set as yet so I guess the boo is stronger than people think in compression and only needs to be improved if you put boo on the back as well since it like most bow woods is stronger in tension than compression.

Graeme

[jkekoni]

If heat treating a bamboo belly,I would be adding the heat only to straight parts and not to the node areas.


Hmmm... No, since I think this would add more compression to the nodes, and I assume they are weaker spots.


Hmmm. Are bamboo nodes weak sponts in compression too, or just in tenssion side?

...
Did not want to discourage the author for trying to invent anything new, the fact that has been invented allready,
means it is a good idea, and most usefull things in this hobby just have been invented allready...

[GraemeK]

Hi Jkekoni

From the work I have already done with boo it does not seem that the nodes are a weak spot in compression.

There are some commercially available all boo bows that have the nodes removed on the belly and this does not give any problem.

I think it works a bit like short pieces of horn glued on the belly and butted up to one another -- even thought they are not connected they can  resist the compression by pushing on one another.

Graeme

[b.bowyer]

 Nice experiment,Graeme.
 I  myself, made a bamboo belly bow with hickory back and maple core . It was a sort of english longbow at the handle but with a little arrow rest cut in it and the limbs were  rectangular in cross section like an american longbow. So there was no glue-up handle. After a fews hundred arrows trough it ,it took more than  one inch of set but remained a fast shooter. Maybee the set came from the hickory being too spongy ( in humid Belgium) and thus too soft for the bamboo belly. I had made before another longbow with bamboo belly and back and it takes  about 2 inches of string follow after unstringing. IMO its a good design (been used for centuries on the japanese yumi ) but the belly should be heat treated.
 By the way ,Graeme, I like your bows very much , especially your recurve, hope some day I can do as good as you.

[GraemeK]

Hi b

I have the same trouble with Hickory, just too humid here to get good results so I gave up trying. At 12 or 13% MC which is what we normally have the stuff is like a limp noodle.
I am going to try an all boo pyramid next and attempt to tiller the belly even though it will remove the nodes since I have seen this done successfully, I will probably temper the belly as well  since this will help to reduce the amount I have to remove by tillering.

Surprised you are familiar with my recurves -- I dont really remember posting them?

Graeme

[Pappy]

Very nice looking bow,great job on that one.
   Pappy

[jkekoni]

GraemeK

I think hickory works well as backing even in humid weater, It just does not work as belly.