Heat treating by radiation

[DC]

That is how Bubby does it, I think. Most of us are too cautious(read chicken )
I found this video. https://www.http://www.scavm.com/blanky.htmyoutube.com/watch?v=EI6K7IHq0a8

He uses lower temperatures but he does say that a few fires have been caused with these which sounds promising. I'm intrigued. More reading

[DC]

I found an outfit, Omega Engineering, that makes these. They make one that's 3" x 24" for about $75can. I'll give them a call and talk about our application.

[Pat B]

Eddie Parker(Mullet) cut holes in the side of a microwave for heat bending bows. I think he stuffed rags around the bow at the holes to seal in the goodies.

[scp]

I got my silicon heating blanket from the biggest online retailer. Not cheap but quite reasonable. I can justify its use as "primitive" because similar effect can be achieved by using several heated stones on top of the belly. I did try to use the smallest iron once. Too flat and stiff bottomed to use effectively. And it will take too long for modern people.
Radiant heat from coal bed or bonfire might be more authentic, but the primitive did use heated stones for cooking. And so far as I know, many old bowyers burnished their bows, especially on the back. They could easily have done the same on the belly with very hot stones.

[DC]

I talked to Omega's tech department and he said that about 430°f is the point at which the heating pad will start to fail and that heating bows might just be too close to the limit. But he did say that if you could keep the temp below 400 it should work.
scp- I'm not to concerned about "primitive". If the end result could be conceivably built by primitive man that's good enough for me. Anything else you can tell me about these things would be appreciated. How many times have you used yours? I'd hate to spend $75 and get 3 uses out of it. Do you control the heater with anything? Monitor the temp? that kind of stuff

[scp]

DC: We probably need to start a new thread, as using a radiant heater is a good topic by itself. My heating pad comes with a thermostat at a similar price. I just used it twice. If you use it following the instruction (I didn't bother), it should last indefinitely. I don't trust its thermostat. Better use an instant or laser thermometer and keep it under or around 170C (338F) for less than 20 minutes. If you see smoke, you better turn it off. Good luck.

[willie]

Willie, those heaters are simple cal-rod heaters. Same as the cooking rings on the top of an electric stove. They will not handle much of a bend before breaking the internal element. They are designed for primarily for conductive (in contact) heat. Used solely in a convection application they will burn out quickly.

Using radiant heat is an option I hadn’t considered. Radiant heat waves heat only the objects the waves come in contact with adding an element of control to the process. so I’ll be keeping track of this thread for solutions to the raised questions.

Beba,
those heaters are a bit long for the rated voltage, and don't get red hot like the stove type. a buddy that installs them reports they can be bent using a tubing bender, at least before they are fired up. he said he never tried to rework one that had been in service.
If you have one it might be worth trying, but after giving some thought to the requirements for bow heating put forth in some of the posts above, I have been leaning towards re purposing a milk house heater. the coil could be removed and hung from something like a piece of stiff but malleable wire or some sort of support that could be easily be formed  into the shape to follow the contours of the limb

[DC]

I have been leaning towards re purposing a milk house heater. the coil could be removed and hung from something like a piece of stiff but malleable wire or some sort of support that could be easily be formed  into the shape to follow the contours of the limb

That's where I've been. I got stalled trying to find ceramic insulators of the right configuration and fabbing reflector/s. I like your idea of hanging the coil from a rod so what we need is insulators with two holes, one for the coil and the other for the rod. Could probably braze reflectors on in between the insulators. Hmmmm

[willie]

Don
keep us posted about the insulators you find. I am looking also. some sort of ceramic filament might be useful.

3d printing can do ceramic parts

thinking about a piece of flexible metal conduit for a support

[Santanasaur]

Maybe I’m wrong about this but I think it might be better not to use  insulation at all. My thinking is that radiative heating hits the belly and absorbs or bounces off before affecting the back.With convection heating, hot air has a chance to go around and scorch the back. This is why I also like using the heat gun close up where you get more radiation to less hot air. If im thinking about this correctly, to get a deeper heat treat before the back starts scorching, air temp should be minimized while as much of the heat as possible comes from direct radiation and not hot air.
in cooking terms I think we want to broil the bow as opposed to baking it, for similar reasons you broil or grill a steak rather than baking it. This is why a salamander broiler in restaurants is open so that it doesn’t heat up and act like an oven. Insulation would make the rig a better oven but worse of a broiler.

On a separate note, if a good way to thermally insulate the back from the belly was found (badgers heat tape post) then convection would work without the issue of scorching the back.

[DC]

The insulators we are talking about is to isolate the heating coils electrically from the structure of the thing. They are just little ceramic buttons sort of. if that's not what you're talking about I'll shut up

[Santanasaur]

Nevermind then DC, I though you were talking about thermal insulation. Id really like to see a safe design with the resistance coil type. The one I tried nearly caught fire in my shop so I moved it outside, but when it rains it shorts out. It was a terrifying and rackety thing.

[brucegeno]

What do you think about using emf protective clothes for heat treating? Just a thought. Sorry for bumping the thread.

[willie]

can you link to something like you are suggesting?
EMF protected clothes sounds like something you would want to be wearing if there was a nuclear bomb explosion nearby

[Badger]

  That looks like an excellent way to heat-treat a bow. I would consider this a major contribution to the craft!