Heat-treat without a form/caul?

[cool_98_555]

Hey guys,

I am working on finishing up another bow that was laying in the corner for a while.  I am going to heat-treat the belly but I don't have a caul/form.  Is there some other way I can get a uniform curve when heat-treating so I can get some reflex put into it?  I don't feel like going to the lumber store and making my own form right now.

[Mo_coon-catcher]

If you have a 2x4 laying around you can get te curve by tillering the limbs to a good even brace. Put a block under the back of the handle on the 2x4, pull the tip to the 2x4. If you had a good even bend at brace it should allow a similar bend going the other way. I’ve done it that way before, and it works well enough. Just be careful pulling the reflex o you don’t risk the belly splitting.

Kyle

[cool_98_555]

Ok do you mean trace the braced profile in the 2x4 and cut to the line?  Or do you mean just put a block under the handle and pulling the tips down to a straight 2x4...because that's just going to result in a relatively straight limb that is reflexed on an angle from the handle, right? Also, by belly splitting you mean cracks in the belly when it is tempered?  I imagine if I were not to put too much backset in the bow when tempering it wouldn't get any cracks in the belly,....am I too far off?  Thanks for the reply.

[Mo_coon-catcher]

The second one is what I’m meaning. Setting the handle on the block and pulling the limbs down. If you have the limbs pretillered they should flex with a curve to them. You can also manipulate the curves by placing other blocks in along the limb to force curves in other places. It’s a good workaround if you aren’t able to cut a curves form in the shape you want but can cut blocks of different sizes.
Let’s say that you start by bending the limbs down with only a 3” block under the handle and it’s bending more in the inner limb than you’d like, place a 2.5” block about 1/3 of the way out. This allows that part of the limb to move that much and the rest of the flex should come from that point on. As long as the limbs are tapered and flexing properly, they should bend around the block instead of linking at them. You can manipulate the shape with these blocks and clamps. Just be sure to pad the blocks though.i do this all the time to manipulate the shapes of forms that I already have. Typically to induce more or less curve than what is already there, or to shift the placement of the curves.

I hope I explained that well enough without pictures.
Kyle

[simk]

i've made the expirience, that if you do so, the first limb heat treared gets way more of reflex as all the strain goes into it when the wood gets plastic there first. when treating the second limb it's therefore maybe better to add a bit more if reflex by elevating the handle a bit more...anyone can confirm this? cheers

[Del the cat]

Yup, like mo' says, but I would only try for a gently recurve.
If you clamp a thin slat to each side it helps stop the heat flowing round onto the back, it also channels the hot air along the belly to give a more even heat and avoid the stripey look.
Del

[Marc St Louis]

You can reverse brace using a natural fibre string, like this

[Pat B]

Mark, I like your old washing machine tub fire pit.     

[ohma2]

Pat B x2

[DC]

Yeah, you can't put a tea can on a heat gun

[Hawkdancer]

Notice the "tea pot" on the left side? 
Hawkdancer

[Stickhead]

I used to use a rocking chair for a caul.  Clamped it upside down in a vise, and used the curved bottom for a form.  Worked pretty well.