water oak

[man at arms]

I have a big water oak stave I split of a large log about 2 years ago with the intention of making a longbow. I started on a stave from the same log, only to find that the grain was twisted. Since then I've done some research. I think I can untwist the bow with steam.

Anyway, what I have is a stave that is 85" long, 5" wide and 4" deep. What I would like to end up with is something resembling an ELB with a draw weight of around 35-40 lbs. This bow will be an ongoing experiment. I will use it to see how much heat treatment and lamination affect the draw weight. Hopefully, I'll be able to derive some equations, or at least some ballpark estimates, from it.

Does anyone know roughly what dimensions I should start with to end up with a bow of the desired weight range?

[crooketarrow]

  What you mean by laminations there are no laminations in selfbows.

  I've never made or heard anyone makeing a water oak bow. But I live a sheltered life so you might want to take that statement with a grain of salt.

[man at arms]

I guess I should say "backing" instead of lamination. Once I've made it, I'll test the weight. Then, I'll heat treat it and test the weight again. Then I'll back it with some kind of cloth with a resin and test again. Then I'll keep adding strips of cloth and testing.

[bradsmith2010]

heat treating may gain some weight,, but the cloth will not,,

[man at arms]

That's what fiberglass kits are, fabric with a resin. I would be making thin fiberglass strips.

I have seen longbows blacked with linen. I suspect it might be more to keep the bow from splintering.

[joachimM]

Ouch, you used the FG-word 
If I were you, I'd try to keep it simple (that's my general advice in any case; complex bows are rarely better, they just require more time to make).
There is little to learn about performance, design and functioning of bows from a single bow, so don't expect too much there.

As for calculations and equations on what to expect from wood bows: there are specific bow design spreadsheets available here and there, where you input wood data, length, desired draw weight and length, bow design etc. and it outputs how it should look like (width, thickness etc) for optimal tiller. That is: a ballpark estimate of the optimal tiller. The real job still requires adjustments, scraping, checking tiller, scraping some more etc .
There's even a spreadsheet version with backings, but you need to know the modulus of elasticity of the materials to use that. These spreadsheets do require quite some investment for them to work, and most people prefer to just make bows from a gut feeling and general bow making wisdom (generously provided by others on this forum).

As for the water oak: it looks pretty comparable to red oak in terms of density and stiffness, but seems to be a bit weaker in compression (from wood-database.com and added to my overview of relative wood tension and compression properties http://www.primitivearcher.com/smf/index.php/topic,50571.msg692410.html). This definitely looks like a species that would benefit from belly toasting. An ELB doesn't seem to be a good design for a compression-weak wood, as ELB bows are nearly as thick as wide, stressing the belly heavily. Adding to a compression-weak wood a very strong backing like fiberglass seems even worse.
 
If I were you, I'd just try to make a 70" pyramid flatbow from that log, 2" wide at fades to 0.5" at tips, and just under 9/16" (14 mm) thick from fades to tip, requiring hardly any thickness taper and slightly toasted on the belly. These dimensions should give you a 40-45# bow at 28", approximately. IMO, such thin limbs are called for in a compression-weak wood.

but hey, that's just the advice of another rookie.