How do you keep from burning the back of the bow when Heating?

[Fred Arnold]

Try as I might I'm still having a problem burning the back when heat treating. I've used aluminum foil which helps somewhat but still not satisfied. Any good tips out there? Do you coat the back with anything?

[Ifrit617]

I use olive oil to coat the belly. Aluminum foil reflects heat so i wouldnt use it, Ive heard of using copper since it asorbs more of the heat versus reflecting it.

Jon

[BowSlayer]

i never heat the back only rub oil into the belly and then heat the belly.  good luck on your bow

[Dan K]

I'm no expert at this but I have been playing around with heat treating. What I have found is the wood continues to cook after you've stopped heat treating. When I heat treat to done it seems to continue to darken so I stop a little before that and it turns out perfect. I just did this last night. If I'm wrong it's no big deal cause I can heat treat again. Hope this helps.

[Dan K]

i never heat the back only rub oil into the belly and then heat the belly.  good luck on your bow

+1

[Del the cat]

If you clamp a couple of thin slats to the sides of the bow this will keep the heat on the belly and stop it leaking round the sides onto the back.
It also directs the heat along the belly which helps give an even heat and reduce the time it takes.
I started using this trick when doing Yew longbows to avoid heating the delicate sapwood back.
It also helps if the bow is strapped to a former that is no wider than the bow, any hot air spilling past the belly is less likely to get deflected under the back.
I'll see if I have any pics on my blog....
Ah! Here we are, the main pic shows two slats clamped to the sides during heat treatment.
http://bowyersdiary.blogspot.co.uk/2013/02/yew-longbow-more-heat.html
Del

[Fred Arnold]

Thanks Jon. I have and have used olive oil in the past. Ill try using it just on the belly where before I coated both back and belly.

Bowslayer, I don't heat the back intentionally, in fact I try to keep as much heat as possible away from the back and sides. The back gets burned on the inside from the heat reflection on the inside of the form where air flow and heat get trapped and have nowhere to go but down.

Dan, you may be right and I may be overheating. What temperature do you try to maintain on your heat gun? I have and old Makita with temperature variation that I generally set between 3.5 and 4 on a 5 scale. I also have the airflow on high. Possibly I should be using the low air flow setting.

Del, I'll give the slats a try. One problem I have is not enough good clamps. A dozen 6" or better are on my bucket list.

[Pat B]

I only use oil when I'm bending wood, not tempering. If you copncentrate down the center of the belly it may help. When tempering I hold the heat gun about 1" or so above the belly and work it back and forth until I get the color I want then move out about 6" and continue, going back over the previous area. In do this out the belly until I reack the end.
 I think you just have to be consciously aware while you are tempering to be sure the heat doean't wreap around the sides to the back.   You could use oil on the back but keep the belly dry. That way you would help prevent the back getting scorched.

[Fred Arnold]

Pat, I think one of the problems is the nozzle on the heat gun displaces too wide of an air flow pattern. Years ago when I was in the leather restoration business I had nozzle attachments with various sizes to concentrate the air flow. Wished I still had them. My shop got broke into and being as well organized as I was back then all of my tools and attachment were stored in separate brief cases. The thieves only had to grab all the tool cases and out the door. I haven't been able to locate any of the attachments online.

[artcher1]

I use forms narrower than the bow ................Art B

[Cameroo]

I use forms narrower than the bow ................Art B

My thoughts exactly. Although some cauls have to be made differently if there are any tip alignment problems, to be able to get sideways clamping pressure.

[mullet]

I don't heat treat on a caul. I put one limb in a wood vice and heat treat the one that is hanging in the air. I also keep the heat gun moving. I keep the gun in one area till the wood starts to turn colors,(black/brown), then move to another 6" section. I've never had a problem burn the back.

[Fred Arnold]

Art, I can see where that is feasible and may have to build a narrower caul so the heat can't get trapped.
Cameroo and mullet, I can see where my problem is partially caused by trying to do 3 things at once on the same form. I'm trying to heat the entire bow and bring the limbs and tips in line, even out the limbs and adding reflex where needed, and tempering the bow all at the same time.