Dimensions for a core in a bamboo backed ipe bow??

[turmoiler]

Hello pals,

 I have a ipe lam wich dimensions are 66" in length, 30 mm in widthness and 5mm in thicknes. I was planning to make a BBI with a 4mm thick bamboo backing, but I think that the ipe lam is too thin and that I will need a core for this bow. The problem is that with ipe a small increase in thickness can make that the bow raises its draw weight a lot and I'm afraid that I have to rasp a lot from the belly if the core is too thick or if the core is too thin ending with an underweight bow.
 I was thinking about 4-6 mm thick jatoba paralel core, I'm aiming for a mild deflex-reflex flatbow in the 45-55 pounds range.
 What do you think of these dimensions for the core?
 Any other idea?

Thanks 

[bubby]

i think you working limbs are only gonna be between 3/8" and 1/2" thick when finished, get your boo thin and go from there, that's how thick mine are and they are 65-70#'s, but that's mine and all wood is differant, Bub

[DarkSoul]

5 mm thickness is scarily thin for a belly. It leaves you very little room for tillering. If you remove too much ipé on the belly during tillering, you'll make it too thin, causing the belly to collapse. It would be good to use a thicker belly lam of ipé. However, if that lam is the only one you have available, you can design the bow accordingly. You should focus on as little tillering as possible. That means the backing and core should be pre-tillered before they are glued up. I would highly recommend a tapered core. A bamboo backing of 4 mm thickness of also a little too thick, I think. 2 mm is very well possible, but 3 mm is about the maximum I personally accept. I'm a firm believer of 'the thinnest bamboo is the best bamboo', but others may disagree. I think you should taper your core, and aim for a total thickness, of all laminations combined, of about 15 mm. near the handle and 12 mm near the tips.
I'm actually currently working on a BBI R/D pretty similar to yours. It'll be around 70" in length though, and about 40-45 pounds. It seems my total limb thickness will be around 11 or 12 mm in most places. A powerlam stiffens up my handle, though. Except for this powerlam, I don't use a core. My ipé is only one lam of 11 mm. and the boo is about 2 mm.
Hope this helps.

Jorik

[mikekeswick]

Yes if your belly lam is only 5mm thick then you have very little room to play with.
I don't think you've got any option other than to taper your core. I normally glue up belly and core do any tillereing or tapering of my core then glue the bamboo on last. A thin bamboo backing will add at least 10 - 15 lbs but it all depends on the amount of crown the bamboo has. Thickness has a big effect on weight.

[markinengland]

With 30mm width and 5mm thickness and a bamboo backing you could make a pyramic bow that would be almost self tillering. I would add a short tapered to nothing central core for the handle/fades section and build the handle up. This, with care should give a reasonably respectable biw if glued up into a bit of reflex. I made a bamboo backed Ipe relfex deflex at around 1.5 inches wide and it pulls over 60lb and the ipe can't be much more than 7.5mm thick.
Good luck,
Mark in England