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Bamboo-Cumaru-(ex-Ipe)-Massaranduba Bow Build-a-long

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Lehtis:
Hei, fellow bowyers!

I´ve recently started this experimental project and my aim is to make an ELB-stylish bow from bamboo, cumaru and ipe. Experimental because of cumaru seems to be rather explosive under pressure but seems to stand well under massaranduba in my earlier bows. Now I´m testing how ipe can handle this task. We´ll see later either a ca. 80 lbs @ 28" bow or fire wood.

So, ca. 5 mm bamboo is on back, belly ca. 8 mm ipe and tapered cumaru as core, ca. 1 cm at handle and 3 mm at limb tips. A slice of scrap massaranduba at handle area to give enough thickness. The slices were glued with Unibond-800, squeezed with rubber band and the limbs were forced ca. 7,5 cm (3") reflex at tips and 3,5 cm at 25 cm from the tips.

In the last picture you´ll see the bow on my tillering system, corners and belly rounded but not drawn with tillering string yet. More to come, stay tuned...

Aaron H:
Your bamboo seems awfully thick.  I have heard,  and from my little experience,  that the thinner the bamboo, the better.  I like to thin my bamboo to about 1/16" on the sides,  which usually equates to about 1/8" or less at the crown.   Someone else with a little more experience may be able to tell you better though.

Lehtis:
Aaron; I´ve heard that also earlier... but few other bows I´ve made have been working fine with that thick bamboo. Latest two 80 lbs and above. Perhaps I´ve got to make bamboo a bit thinner next time.

Lehtis:
Some additional thoughts about bamboo thickness on bow´s back: I think (and may be wrong...) it´s also related to the thickness of the whole limb also. ELB stylish rounded belly should allow thicker bamboo backing than flat bows. In my bows 4-5 mm bamboo is  ca. 1/4 from the mid limb total thickness. Also, more bamboo at limb tips should give more speed because of it´s lighter than heavier core and belly woods.

Lehtis:
No firewood (yet) but no bow either (yet)... I did preliminary tillering with long string and when I was changing to short string to finalize tillering I heard unpleasant noise. I found some longitudinal marks on the upper limb between the handle and mid limb showing ipe growth rings starting to separate. Either a hidden damage in the wood structure or ipe simply doesn´t stand the compression from cumaru and bamboo.

May the stave rest now for a while. Later during this winter I´m planning to sand all that ipe away and also thin a bit cumaru core and then glue my last massaranduba as new belly.

Until then: Season´s Greetings & Happy New Year 2016!

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