Help avoiding scorched back when heat treating?

[upstatenybowyer]

This has been happening especially when adding reflex against a simple caul. I think the heat gets trapped between the bow and the caul. Crowned staves are worse. I guess I could thin the caul so it doesn't stick out to the side of the bow. Any thoughts?

[Danzn Bar]

Patience ..........drop the heat gun temp down a notch, pull it back an inch or two and slow down.....patience.. from experience.
DBar

[osage outlaw]

Can you post a picture of your caul?  Are you trying to heat it to quick?  Are you holding the heat gun so it blows on the belly of the bow or on the sides of the limbs?

[DC]

I tried making a 3/4" caul for that reason but found I couldn't bend the bow sideways if I wanted. The bow was stronger than the caul.

[upstatenybowyer]

Can you post a picture of your caul?  Are you trying to heat it to quick?  Are you holding the heat gun so it blows on the belly of the bow or on the sides of the limbs?

I hold it directly over the belly about 4" away. Maybe it's happening when my arms get tired and I unknowningly lower it. Sounds like slower and further away is the key.

[osage outlaw]

Are you holding the heat gun in one spot for a long time or do you keep it constantly moving? 

[Mo_coon-catcher]

I just hold the gun at about a 45* angle to the wood and keep it moving. I go slow enough that you don't want to hold your hand on the wood once the gun passes. Then just keep doing slow passes until the wood get to the color you like. The only time I have issues with a little edge and back scorch is when I try bending out a side kink and I get in a hurry. I think that between concentrating the heat in one spot and the heat rebounding onto the back. Though I've never had an issue from a light toasting on the back.

Kyle

[DC]

I made a jig to hold the heat gun. It's hard to hold it an even distance away for 45 minutes.

[upstatenybowyer]

I've been meaning to make one of those DC. I think Marc has a pic of one he made in TBB 3.

Moon that sounds like a smart way to do it. I've been staying on one spot until it browns up and that could be the problem.

How do you guys add reflex? I usually clamp near the handle, start heating and bend and clamp as I go. I never want to bend the wood into reflex while it's cold.

[Pat B]

I hold the heat gun 1" to  2" above the belly working it back and forth over a 6" area. When that area is chocolate brown I move out to the next 6" going back over the previous area(s) until I'm at the end of the working area of the limb. Once it's all tempered and the clamps are in place I go over the entire limb again then let it cool over night at least before I unclamp it.  Doing it this way I can lightly temper a limb in 30 minutes or less.

[bubby]

One thing i think is important, if your caul is charred you need to sand it down. Once it is charred it is charcoal basically and it ignites faster than uncharred wood and will char the back faster with less heat

[Del the cat]

clamp side cheeks to the edges of the bow.
http://bowyersdiary.blogspot.co.uk/2015/02/two-steps-forward-one-step-back.html
This youtube video shows it in action:-
https://www.youtube.com/watch?v=kM1_A2A0_TI
Del

[mikekeswick]

It is very simple - just make your form narrower than the bow.
If you need a form to bend limbs sideways etc then make a separate on that is up to the job.
Mine is a piece of oak 1 inch wide and 4" deep.
Making a holder for the gun is pretty much essential if you are going to be doing more than a few heat treated bows. Forget holding it.....BORING!

[Pappy]

I do like Mike, 1 for straightening and reflexing and one for heat treating if I decide to do so. 
 Pappy

[upstatenybowyer]

These comments are amazingly helpful. Thank you kindly gentlemen