steam gun

[Pat B]

Graem, Thanks for that explanation. 
  I guess a typical hot box will work for a stave oven. My box has a thermostat that maxes at 168deg. It takes 4 light bulbs, anywhere from 60w to 100w. I regulate the temp by changing bulbs or just unscrewing a bulb or 2...or 3. One 100w bulbs will keep the box at about 90degs good for storing wood and maintaining lower M/C. I sometime pre heat a stave or almost bow in the hot box for a while before straightening.    Pat

[Badger]

Good info Graeme, I have seen staves become checked while recrving with steam, presently I do it just as Pat described but have found some white woods that just don't seem to respond to dry heat as well as I would like. Steve

[Justin Snyder]

The problem with dry heat is that some woods like Ipe tend to burn before you can heat them enough to bend.  I imagine an oven set to 150* would heat it throughout, but it might dry it so bad that bending would cause fractures and splinters. Not to many woods like 2% MC.  I know that heat makes some changes in the wood, but many self bows have been built from kiln dried wood that has been heated well beyond 150*.  Many kilns now rapidly raise the temp to 400* to dry. By keeping the moisture high inside the kiln until the temp is reached it reduces checking. I think it is worth a try. Justin

[Badger]

Many years ago I had fashioned a solar heater where I used black plastic pipe and a little moisture inside with wet rags. I would use rubber or some other spring clamp type thing to lash a bow into the shape I wanted and then leave it in the sun for a week or two until the shape held. It actually worked pretty well. Steve

[mullet]

 Well, what Graem has said explains a lot of ruined hickory stave's for me. I made a boiler out of a drive shaft that I could put on my propane turkey cooker. I could boil a whole limb at once. I had so many failures with the limb just collapsing that I quit using it. I didn't know I was destroying the wood getting it that hot.

[Badger]

   Some good research on how steam and heat affect wood might be a good addittion the next time bowyers bibles come out. I know the heat treating Mark St Louis made popular has had a major infuence on todays bows. Interesting how too much heat can severly damage the wood if not applied right.

[mullet]

  Wow, I could probally write that one. I've destroyed some wood trying to use my boiling tube. 

[GraemeK]

Hi Justin
The temperature thy run drying kilns is very high but you can only get away with this while the timber has a high MC and if you can control the the humidity in the kiln because this stops the timber actually getting to the temperature of the kiln. As the MC of the wood drops usually the heat programed for the kiln does too or you get cellular collapse.
I have not worked with Ipe but in general it is considered that wood can withstand 65 deg C (about 150 deg F ) for periods of days without measurable changes to physical properties after the timber has regained its appropriate moisture content. I have found this to be true with the woods I have worked with and I think there are some misconceptions about the affects of heat on wood that are result of people being unaware of just how hot they are getting the timber with localized heating and how long it takes to heat evenly all the way through. If the surface of the wood is going dark brown there is a good chance that the temperature is in the of 300 to 500 deg F region and that is really way too hot ( the Indians reckoned if you discoloured the wood while heat treating it was a sign of a lack of skill ) The other part is that I doubt that many people ever get the core of the timber to suitably hot or at least do it without getting the outside too hot so I think the concept of what may be possible with controlled oven heating is biased by this.
If I had a little more time I would do some definitive testing so we had accurate data to work with -- I will put it on my to do list but is depressingly long at the moment.

Graeme

[woodenwonder]

What about sealing the entire bow with shellac before putting into an 150 deg oven? Or maybe use a heat blanket instead? But what would you do with an entire palletable bow? Unless you had a full length bow press. I might try out a heating pad on piece of wood shellaced or wrapped with plastic sometime. Has anybody tried a heating blanket?

[brian melton]

Steve,

              Where is the conversation about the micro-wave? Thats what I use....