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Author Topic: Tempered belly is also yielding a toasted back  (Read 3773 times)

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Offline Knoll

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Tempered belly is also yielding a toasted back
« on: January 14, 2015, 03:24:01 pm »
Recently finished a reflex caul.  Used it 3 times thus far to temper ash & hickory bellies.  But am getting toasted-brown backs too.  I'm tempering each limb 30-45 minutes in sections of 6-8", and then clamp down each section.  Heat gun is pointed mostly straight down at the limb, not directed much at angle from sides.
Is toasting of back typical, or are there techniques for reducing/eliminating this?
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Offline bushboy

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Re: Tempered belly is also yielding a toasted back
« Reply #1 on: January 14, 2015, 03:38:19 pm »
The narrower the caul the better within reason.does your caul have a back board?
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Offline Pat B

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Re: Tempered belly is also yielding a toasted back
« Reply #2 on: January 14, 2015, 04:32:24 pm »
Toasting the back is bad. It can weaken it.
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Offline Del the cat

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Re: Tempered belly is also yielding a toasted back
« Reply #3 on: January 14, 2015, 04:37:09 pm »
A narrow former and clamp a thin slat of wood to either side of the stave. This also directs the heat along the belly and speeds up the process a tad.
If you look closely at the pic in this post you'll see what I mean.
A few layers of masking tape between the edge of the stave and the slats helps stop any leak through of hot air)
http://bowyersdiary.blogspot.co.uk/2014/08/heat-treating-belly-billets.html
I use this a lot with Yew where you don't want the nice white sapwood scorched.
Del
« Last Edit: January 14, 2015, 05:17:41 pm by Del the cat »
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Offline DC

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Re: Tempered belly is also yielding a toasted back
« Reply #4 on: January 14, 2015, 05:28:15 pm »
Would one of those diffusers help? They slide over the end of a heat gun to spread the heat. I was thinking of turning it 90 degrees to narrow the heat flow. I have a caul made from a 2x6 and I scorched the back of the yew I'm working on. It was just a little scorch and so far it hasn't hurt it, touch wood. I think I'll make a new caul ouy of 3/4" plywood.
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Offline Knoll

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Re: Tempered belly is also yielding a toasted back
« Reply #5 on: January 14, 2015, 06:04:00 pm »
No, bushboy,, there's not a back board on it ... yet.  It is kinda wide.  Screwed 1x and a 2x together, so it's about 2 1/4" wide.

Del .... will give that a try.  Also, your setups always look so well thought out!

Thanks, all!!
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... alone in distant woods or fields, in unpretending sproutlands or pastures tracked by rabbits, even in a bleak and, to most, cheerless day .... .  I suppose that this value, in my case, is equivalent to what others get by churchgoing & prayer.  Hank Thoreau, 1857

Offline duke3192

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Re: Tempered belly is also yielding a toasted back
« Reply #6 on: January 14, 2015, 08:40:44 pm »
I would suggest that you go to an auto-parts store and get a infra-red thermometer and practice on some scrap wood and determine your heat range.
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Offline bushboy

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Re: Tempered belly is also yielding a toasted back
« Reply #7 on: January 14, 2015, 10:10:04 pm »
With a back board it's worse. I wet a cloth an place it at the right angle to prevent this when toasting.
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Offline bubbles

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Re: Tempered belly is also yielding a toasted back
« Reply #8 on: January 17, 2015, 12:57:00 pm »
I have had this problem any time there is something right behind the bow that is wider than the bow.  If i was taking out a bend on a peice of wood and i shoved a shim under the back to get the bend out, the back would toast right around the shim,  if the shim was wider than the bow. I guess anything wider directs the hot air around the back, toasting it as well.
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Offline Eric Garza

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Re: Tempered belly is also yielding a toasted back
« Reply #9 on: January 17, 2015, 02:09:54 pm »
Something I've started doing is heat treating a bow before narrowing the limbs. I've gotten into the habit of doing this because sometimes heat treating warps the wood, so rather than heat treating and then heating some more to correct warp I can just draw a new center line and make minor adjustments to the layout to accommodate warp.
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Offline Del the cat

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Re: Tempered belly is also yielding a toasted back
« Reply #10 on: January 17, 2015, 02:10:40 pm »
Quote from: Knoll on January 14, 2015, 06:04:00 pm
No, bushboy,, there's not a back board on it ... yet.  It is kinda wide.  Screwed 1x and a 2x together, so it's about 2 1/4" wide.

Del .... will give that a try.  Also, your setups always look so well thought out!

Thanks, all!!
That's the trick spend more time thinking planning and setting up than actually doing the job  :laugh:.
Del
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Offline Knoll

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Re: Tempered belly is also yielding a toasted back
« Reply #11 on: January 17, 2015, 08:06:35 pm »
Quote from: Del the cat on January 17, 2015, 02:10:40 pm
That's the trick spend more time thinking planning and setting up than actually doing the job  :laugh:.
Del
The Wife accuses me of the same thing . . . . . .
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... alone in distant woods or fields, in unpretending sproutlands or pastures tracked by rabbits, even in a bleak and, to most, cheerless day .... .  I suppose that this value, in my case, is equivalent to what others get by churchgoing & prayer.  Hank Thoreau, 1857
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