Heat tempering bow limbs

[burchett.donald]

     Information wanted on tempering bow limbs. I understand we temper the belly to colapse the wood cells to aid in holding reflex. How hot do we get different woods, I see some very dark scorched areas in some build along videos. Once I see a SLIGHT color change I feel I'm done. Could anybody shed some heat on this subject. We don't want to weaken limbs. I don't think we need to get wood so hot it starts changing to a dark color.

[Ifrit617]

you want to temper the limbs till they turn a chocolate brown color and you can smell the wood "toasting". This color change is mostly on the surface and does not weaken the wood. When you temper the wood, remember a simple rule...

"Brown is good, black is bad!" 

hope this helps.

Jon

[k-hat]

First, it's the belly you heat, never the back   If you're shaping, i believe i read somewhere the core of the limb needs to get to 140degrees F.  This doesn't necessitate toasting the belly, but invariably does some if you use dry heat.  When shaping, i put the heat gun on the belly and heat until the back is just about too hot to touch.  that tells me the heat has soaked through enough to keep the shape in the limb. 

As far as tempering, the color change depends on how fast you heat it and use of oil/fat or not.  Just like a piece of bread, you can scorch the outside without hardly heating below the surface.  This is not desirable if you're wanting to temper the wood. 

I'm still a little green at this, so hopefully someone will chime in more knowledgeable.  Marc St. Louis has a great video on this website where he shows the whole process. 

[Del the cat]

My first attempts had been too hot too quick. PA and TBB IV helped considerably.
I then got a temperature controlled heat gun quite cheap, which helped a huge amount and got some useful quantitive data which appeared to be lacking elsewhere.
It should take 30-40 minutes at least to do one limb, and it takes a fair bit of time before any colour change is visible.
I'll attach my notes. They are just notes so will read a bit weird.
Del

Heat treating/bending  temperatures.   27/3/11(Note all temperatures in degrees C)

250 for bending won’t scorch the wood, but it will brown it slightly when kept in with aluminium foil (Yew)… maybe 210-220 would be better (yes that’s safer , be carefull not to forget it and leave it cooking for an hour!).
 I protect the sapwood back with masking tape and duct tape, rub a bit of beeswax on the belly to help spread the heat/stop scorching.
30/04/11
350-400 for heat treating. (anything over 250 will brown)
Currently using 310-330 on the  Yew longbow I’m doing for myself, heating in a bit of reflex and tempering the belly all at once on the roughed out bow. Aiming for a fast  50 pounder which is what I’ve now got, 99% of the reflex has pulled out leaving a straight fast bow.
Osage:_
Straightening and tip recurving.  200C 15-20mins using aluminium foil shroud to spread heat and keep it in. Thin steel strip on outside of bent to spread load and help stop splintering.

[Gordon]

I apply heat until the wood is medium to dark brown. I've had much better success when the heat is applied slowly - it takes me about 1 hour per limb.

[Del the cat]

BTW. Another of my early mistakes was not allowing enough time for the bow to recover after heat treatment. I try to give 3 days after any heat treatment or heat bending. Not always easy 'cos I'm an impatient git.
Del

[mikekeswick]

The bread anology is quite good - black toast is bad but somewhere between medium light brown to light darkish brown is good ........
Heat treating is just a fanastic process and we have a lot to be thankfully for when Marc wrote the chapter in TTB4 - thanks Marc 

[Del the cat]

The bread anology is quite good - black toast is bad but somewhere between medium light brown to light darkish brown is good ........
Heat treating is just a fanastic process and we have a lot to be thankfully for when Marc wrote the chapter in TTB4 - thanks Marc 

I find the butter and marmalade isn't as good as Danish Oil .
I'll have to try that 4 strand string and a lightish arrow see what I can squeeze out of 'Twister'
Del

[Cloudfeather]

I'm planning on doing some tempering to the black locust bow I'm working on. It's near floor tillered. Would now be a good time to do the tempering?

[adb]

Purchase TBB4 and read Marc St Louis' chapter on heat treating. Very detailed.

[BowEd]

The way I understand it wood will plasitcize at 350 degrees.Slow and easy is the ticket here.You want it to pentrate as deep as possible.I use a laser thermometer and usually a spot will get 400 degrees for about a minute and then I'll move on.Hickory & elm will brown slower than black locust so I keep my gun about almost 5" away from black locust so it does'nt get very black just brown.
When inducing reflex unless the bow is very close to thickness dimensions a cold over all clamping can produce a tension crack.I put my c clamps not much more than 4" in front of the area that I'm heating to avoid this better.

[burchett.donald]

Wow this is an old thread that has been resurrected. And yes, since I have treated white oak this way and went to a brown toasty color with no problems. But never black and charred. Use a heat gun and a wooden mount to hold it. It took about and hour and a half to do the last floor tillered bow. So yes Sled after floor tiller is the time to heat treat for me.