Bending an Osage core

[Elnathan]

Greetings!
I have a question that I hope y'all can answer. I have a sawn piece of osage that I bought off ebay seven years or so ago, along with a piece of hickory for a backing, but never glued together, because the suface to be glued had some to some tearout from the planer and all my attempts to fix it made the situation worse. Recently, I went back to it and succeeded in getting it flat, only to find that it has warped slightly into a slight s-shape. I would like to straighten it out, but am unsure of the proper way to do so.

The core/stave (Is it a stave w/o the backing, or just a core?) is about 1 1/2 inches wide and 7/8" thick. That is pretty thick to bend, I'd imagine, but I don't really want to cut it down before I glue the backing on, and I don't want to try bending it after the backing is on  for fear that the heat or moisture would compromise the glue joint. On the plus side, the bends are not terribly great: as it is now, one limb has maybe 1/4" curve away from the string (mid-limb) and the stave has about an inch of string-follow built into it (probably more once I straighten the limb). I suppose it is possible to use it as it is, but I hate to just ignore a problem that will affect final product or make life difficult later on if I can fix it now. The osage has very curved grain that the saw just cut right through, and the pattern of run-off sort of dictates which side become the belly - I think it will be less durable if I just flip it around, and since I suspect that it is a marginal piece to begin with (probably why I was the only bidder), I want to be as careful about such things as I can.

I have access to a heat gun, which would be the simplest way to do things by far, but since I am going to be gluing it afterwards I am not sure if I should use grease or not. Or should I use steam?

I would appreciate your advice. I have a fair bit of woodworking experience, but have never done any serious bending nor have I made a bow before, so I am a little bit out of my depth at the moment.

Elnathan

[Pat B]

Were you gonna add any reflef or deflex to the core? If so you can eliminate the twist at the same time with a form, clamps and heatgun. Then later glue it up to the backing.

[Elnathan]

I just want to get it straight. There is no twist (well, my winding sticks say that there is a very, very tiny twist - probably  no more than 1/64" over the six-foot stave, but I think fixing it would be more likely to hurt than help), it is just that it bends towards the string in the middle of the stave and then back away from it on one limb.

What I would like to do is use a heat gun and clamp it in my portable workbench (it has what is basically a vice with 30" jaws). That would be the simplest solution. I am not sure if I should use grease or not, or whether steam would be a better choice for something that has to be glued afterwards. While I have read many things on how to bend osage, I can't find anything specifically on bending laminates.

[DarkSoul]

You don't need to either heat or steam straighten it. Since you'll be glueing down a wooden backing, you can force the blank in any shape you want while the glue is drying. Reduce the osage to a floor tillered blank (this is a very important step). Then glue down the hickory backing and 'clamp' it down with bike inner tubes. Then use a few clamps to add a few inches of reflex or a nice reflex/deflex design. Leave for at least 24 hrs so the glue can dry, before unclamping.
Pretillering the core allows you to easily force the blank straight, while the hickory backing keeps the blank in  place and prevents spring back.

[Roy]

I build a lot of Bamboo backed Osage Bows, Hickory backed Osage would be no different. I cut my bows profile out of the boo, then glue it onto a 1 1/2 wide Osage belly slat, which I have pre tapered thickness wise from 1/2 thick at the center of the handle out to the fades, then tapered to 3/8th thick at the tips. Before glue up I center the boo with a string ran end to end, which is exactly the shape of my bow, onto the 1 1/2 wide belly slat. I then draw the boo outline onto the belly slat and then cut about 1/8th inch outside of the line to narrow the belly slat so it bends a bit easier. It will bend with good heavy clamps. I do deflex/reflex glue ups, here is a video of my form and glue up. Make SURE you pad the hickory backing with blocks of wood or the pressure from the clamps will indent it, also wrap the bow with plastic wrap before glue up to prevent a mess with the glue running all  over the place. If you use heavy rubber straps then you don't need to worry about the padding of the hickory. The slight 1/64th twist will go away after glue up.

http://www.youtube.com/watch?v=MGXmqFxUjHU

Here is the bow from that glue up.

[Elnathan]

Thanks guys. One option of just guing it together and relying on the backing to keep it straight was one of the first things I considered, but I don't think it would work in thuis case. The problem with just gluing the backing on and relying on that to keep the stave straight is that the backing itself is a bit snaky - another s-curve, but side-to-side instead of back-and-belly - and thus trying to glue the stave straight while dealing with two different pieces of warped wood looks like it would be a nightmare. Far better to get the core straight, and then deal with the backing separately. I am also not really keen on the notion of floor tillering it without a backing on it, given the wonky grain.

[Pat B]

Are you using a form in the glue up? If so it will straighten out the belly and backing.