cauls and fire hardening

[Fox]

Okay I've been given the advice to try fire hardening, I have only done this once or twice and I didn't do the best job either time.  I watched a video or two on it and have a better understanding. I made a full sized caul which took my forever since I went and cut a poplar hued it and then made a caul from that, which was pretty fun to do...

now my question are, how do I make sure both sides of the caul are the same and will induce the same reflex  on both limbs? second question is, the bow I'm about to fire Harden I've already tillered almost to full draw so its not super thick anymore, how long should I fire Harden it for?

Untitled by
Livvydog, on FlickrUntitled by Livvydog, on FlickrUntitled by Livvydog, on Flickr

[bambule]

I cut a log  in half and screwed it together. Then I use my bandsaw for the form of the caul. After that, I unscrew the two parts and put them in the middle again together with screws. So both sides are the same.
The time for fire hardening depends on the amount of charcoal and the distance between the caul and the coal.
Check your clamped bow every 5 minutes and stop when it looks good enough - a brownish color is a good result.

[Pat B]

You need to give that caul plenty of time to dry and it could twist and check while it is drying. A 8" 2x6 from a lumber yard would be a better choice for a stable caul.

[PaSteve]

Agree with Pat about the caul.  As far as fire hardening exactly what bambule said. Heat from the coals and distance from the heat will dictate how long the process takes. Definitely, keep a close eye on it. It can go from properly fire hardened to burned quickly especially if it's a little too close to the heat source. Found that out the hard way.

[Fox]

I’m not too worried about the caul warping I’ve made a few one limb cauls the same way with no problem. That makes sense to cut it and half and make them the same that way… bambule It looks like you have tinfoil on your caul any reason imperticuler?

[superdav95]

Fox.  I agree with what’s been said already too.  Only thing I’ll add is that I only use select dried lumber to make my calls from that way I get no twisting or sap leakage from knotty pine.  I go full 2” wide select too.  Costs little more but it lasts way longer for me anyway.  As for the heat treatment.  I only use hardwood coals.  I gauge the heat with my hand to get a sense of how close I suspend the form with bow clamped to it above the coals.  If I can’t hold my hand at the level of the bow belly for more then 1-2 seconds it’s about right for a slow bake that’s pretty safe.  But like already said I would check very regularly to ensure not burning too much.  I go for dark brown on my hickory but don’t go as dark on other white woods FYI.  I’ve learned that some white woods bake little bette then others.  2-3 hours should do it.  If your bow wants to fall off the clamped form then it’s likely baked enough.  Good luck and have fun!

[Fox]

Thanks superDave, that’s super helpful with how to tell how close to the coals to have it 

[bambule]

The tinfoil is for reflection - so that the back of the bow is not burned. Works well but you have to check it - if it‘s too hot or the caul is too near to the fire even the tinfoil will not prevent the back from getting black.

[superdav95]

Fox,  no problem my pleasure.   One other thing I’ll add.  I’ve since acquired a infrared high heat thermometer and tested the heat on the belly of my bows while baking and it’s usually between 250-300 Fahrenheit.  Hope that helps some too.  If you have a digital thermometer to use or just the hand works.     

[Pat B]

Bambule, be careful with the foil on the caul. I did that once and the heat from the heat gun curled around the stave, reflected off the foil and scorched the back.

[superdav95]

I’m with pat on not using the foil.  I’ve had good results with bare cauls and adjusting the distance the belly is from the coals and constant monitoring.  Good slow bake is the best way. 

[bambule]

Thank you for your care. I`ve done it several times with tinfoil without any problems with the heat gun and with fire.
But I will think about it for the future.

Greetz
Bambule

[Eric Krewson]

Darin Putman is very experienced with ins and outs of fire hardening over a charcoal pit.

The last time he shared his findings on a bunch fire hardened hickory bows here complete with chronograph results, weight loss, and moisture absorption rates the know it all keyboard warriors here shouted him down and ridiculed him. He may just keep his information to himself this time.

He recently cut and stockpiled a huge amount of sweetgum bow staves to continue his testing on, the results should be interesting.

[Fox]

What were his findings from the hickory Eric?

[Eric Krewson]

He used hickory, he found off the charcoal pit the bow was an exceptional performer but unlike what was stated in the video, his bows stored outside in his show gradually rehydrated and lost most of the earlier benefits.