More heat treating

[DC]

Has anyone noticed that some woods seem to heat faster than others? When I heat Ocean Spray the surface temp of the wood will go up to about 375°f or so and just kinda sit there for a longish time, then it will creep up to the 425°f that I want. I was just heating a piece of Pacific Nine Bark(another dense wood) and it seemed to go right to 425 with no delay and quite quickly too. I always keep the gun about 3 1/2" from the surface and if anything the Nine Bark would have been wetter. I realise that most of you have never even seen these woods and probably only a few more monitor the woods temp while heating it but maybe other woods behave the same. Any ideas why?

[Bryce]

Yep heat takes a bit longer to get through denser woods. The temperature on the back of the bow is what I like to feel for.

[bassman]

Yes, and cool faster. Maybe wood density.

[Badger]

 DC, do you heat one spot and then move once it reacjed temp or keep your heat gun moving th entire time. To me it doesn't seem possible for the heat to move through the wood fast enough to make heating in one spot effective but I do know a lot of folks do it that way. How long does it take you to do a limb?

[Bayou Ben]

Water has a higher thermal conductivity than wood.  So it makes sense that the wetter wood will get hotter quicker.

Density plays a part too.  The denser wood will get hot quicker.  Imagine heating a piece of metal vs a piece of foam. 

[DC]

DC, do you heat one spot and then move once it reacjed temp or keep your heat gun moving th entire time. To me it doesn't seem possible for the heat to move through the wood fast enough to make heating in one spot effective but I do know a lot of folks do it that way. How long does it take you to do a limb?

Heat one spot and move along. I tried waving it around and my arm about died after 10 min . Not to mention the boredom. It takes forever to do a limb(about 1 1/2 hours I think) and I usually try to do little things like weigh staves that are drying just to break the tedium.

Water has a higher thermal conductivity than wood.  So it makes sense that the wetter wood will get hotter quicker.

Density plays a part too.  The denser wood will get hot quicker.  Imagine heating a piece of metal vs a piece of foam. 

I never thought of it that way. I was thinking that the moisture might cap the temp at around 212° and slow it down(kinda water cooled) but what you're saying makes sense. I agree that denser will get hotter quicker but in this case it was the reverse. OS has an SG of 1.2 and Nine Bark measured .9. Both very dense but still.

PS I just looked back and Bryce thinks that denser conducts slower. So 1 and 1.

[DC]

Yep heat takes a bit longer to get through denser woods. The temperature on the back of the bow is what I like to feel for.

I usually have them on a caul and can't reach the back. I have cut notches in the caul so the laser thermometer can "see" in there but you can only cut so many notches.

[SLIMBOB]

Thermal conductivity increases with density and moisture.

[Badger]

  I hold the heat gun right on the wood almost and do the entire limb at one time moving it from one end to the other. It takes me about 20 min for the back to be too hot to touch and to get the color change I am looking for on the belly. I recently did a hackberry bow which is not very dense and it took a lot longer to get hot. The surface will get hot quicker but takes longer to penetrate

[DC]

I might be able to stand 20 min. I'll give it a try next time. Last time I tried it I didn't hold the gun right up close.

[Badger]

DC, I have the 1500 watt masters heat gun. Not sure if the gun you are using puts out as much heat.

[bownarra]

Hazel takes a while and it isn't very dense at all There is something else at play not just density.

[Selfbowman]

I use a Milwaukee heat gun 1200-1500 watts. I heat 4-6” at a time takes me about 20-30 min. per limb. Where do you get that thermometer??? I guess at the heat by feel!  Arvin

[Bayou Ben]

Do you guys weigh your bows before and after heat treat? 
I just did that and got 19.9 oz before, 19.1 right after, and a day later(today) it is 19.3. 
Got me thinking I bet the surface MC of the wood has to be almost 0 after a deep heat treat. 

[DC]

I got a laser thermometer on sale at Canadian Tire for around $20can. It's one of the things they put on a good sale quite often. it's fun to play with but I wouldn't buy one unless it was a deal.
My gun is 1200 watts.
I did weigh one before and after once but i don't remember the numbers. It wasn't much difference though.