Heat Treating Idea

[jasonoflivingston]

So, I had a thought the other day and I am curious to know what you guys think.  As it stands, there are several common ways to apply heat treatment to the belly of a bow such as a burner element, heat gun etc.  These all involve indirect heat application using a source that is at a higher temperature than I am guessing is required on the surface of the wood to achieve the desired result. 

I am wondering if it would be possible to heat treat with direct heat application to the wood using a controllable heated surface of equivalent temperature to what is applied through the indirect methods. 

First off, am I crazy.  Second, does anyone know how hot you must get the wood and for how long for heat treating to work well?  I have a heat source large enough to do whole bow staves or whole limbs at time and at any temperature up to 250 Celsius (I believe wood starts burning at 232 Celsius). 

My thinking is that, if this is possible, doing a whole limb in one shot or even a whole bow would provide the most even treatment possible.  Of course, this probably won't work for character bows full of knots and irregularities.       

[burchett.donald]

Jason, I have soaked mine in a hot box that I have left over from my trad making years that has light bulbs and a thermostat just to stay dry during tillering sessions. But on a cull with a heat gun is my favorite way because I like the freedom I have to move limbs and clamps...Don't know the exact temp for bending or heat treatment though. I don't think I would want to put an extreme amount of heat on the back of the bow, the belly yes, like to turn it dark...
                                                                                                                   Don

[Badger]

   It's only about the bottom 1/8" of the belly you are really concerned with. I changed my method several years ago. I never toast anymore. I wave the gun from one end of the limb to the other on high heat, I have masters that puts out a lot of heat. I do that for about 7 or 8 min until the limb just starts to deepen in color. The back of the limb is too hot too hold you hand on at that point. You need to be able to adjust the limb as you heat.

[RBLusthaus]

I really try hard to keep heat from the back of the bow so, say, putting the whole shebang into a pizza oven would not work for me.

Russ

[jasonoflivingston]

My heat source is an automated, heated, vacuum table, ie. there would only be heat on one side while the other would be open to the air.  If I wanted to get really fancy, I could create a heat transferring form and use the vacuum membrane to apply pressure for bending. 

That being said, the proposed method is anything, but primitive.  Personally, I use a heat gun in a similar fashion to Badger.  I was just curious if this might work as it has some positive process implications and may hold some interesting information on actual desired temperatures and duration of the treatment process.  Perhaps I will try some experiments.     

[Marc St Louis]

I measured the heat once at the wood surface using a candy thermometer and if I remember right it was between 350 and 400 degrees F

[jasonoflivingston]

I measured the heat once at the wood surface using a candy thermometer and if I remember right it was between 350 and 400 degrees F

Thanks.  That helps to provide a good starting point.  When I get some time, I will use a heat gun on a sample while measuring temperature on both the back and belly of the sample.  I will use your numbers as a representative starting point for belly temperature.  Then I will attempt to recreate that with direct contact heat on the belly.  Monitoring the backing temperature at the same time will help to determine an adequate dwell time for an equivalent depth of treatment.   

Beyond that, I am thinking of experimenting with heat on the belly and some form of heat sink/cold source on the back with the intent being to isolate the treatment to just the belly and prevent it from degrading backing performance.   

Since I am not sure making several identical bows is the most feasible for me at the moment, I will have to come up with a test to compare performance results.