heat treating/ fire hardening and colour change

[PatM]

The experience of Bamboo flyrod builders seems to mirror our experience.   Of course we know bamboo is grass and not wood.

 I wonder if Marc is thinking of Dick Baugh?

 Here's the bamboo tests:
 http://www.powerfibers.com/BAMBOO_IN_THE_LABORATORY.pdf

[Eric Krewson]

Pretty sure it was Badger that did the testing, he had pictures in his post as well on how he did it.

[scp]

Heat can weaken wood's tensile strength, mainly by damaging cellulose. But heat can also strengthen its compressive strength, mainly by affecting lignin.

Using silicon heating strips on the bow's belly only, I try not to damage its back, while strengthening its belly. I go all the way up to the temperature that plasticizes lignin just near the belly. The belly of the bow would be browned, but its back would never be.

[Marc St Louis]

The experience of Bamboo flyrod builders seems to mirror our experience.   Of course we know bamboo is grass and not wood.

 I wonder if Marc is thinking of Dick Baugh?

 Here's the bamboo tests:
 http://www.powerfibers.com/BAMBOO_IN_THE_LABORATORY.pdf

Yes it was Dick who did the testing. 

I think it's time for Tom to say goodbye

[bassman]

I have heat treated bows were the back is very hot to the touch  with no ill effects. I do it ,because I feel I am getting the full benefits of the heat treating method. May not be right in many bow maker's eyes, but it works, and that is really what counts.

[JW_Halverson]

The experience of Bamboo flyrod builders seems to mirror our experience.   Of course we know bamboo is grass and not wood.

 I wonder if Marc is thinking of Dick Baugh?

 Here's the bamboo tests:
 http://www.powerfibers.com/BAMBOO_IN_THE_LABORATORY.pdf

Yes it was Dick who did the testing. 

I think it's time for Tom to say goodbye

I already don't miss him! 

Now that the housecleaning service has dealt this the matter, shall we get back to work?

To my mind, there are two extremes of heat treatment, both being of zero value. First would be toasting a bow until the entire thickness of the bow has reached the same temp as the belly and the bow is ruined because the back now will not handle the tension. The other would be toasting so rapidly that only the very thinnest surface layer of the limb actually has change, as often signified by the change of color, yielding virtually no measurable change in the behavior of the wood under bend.

How to heat to a consistent depth along the entire belly of the bow without compromising the back of the bow is where the skills part of the equation comes into play. Whatever means you choose, you need to control both time and temperature, with each of the two variables affecting the other in real time! I think having a clock on the bench as well as one of those fancy infrared temperature sensor guns would go a long way to helping someone generate some consistency, but a lot of us are going by keeping a slow count in our heads and watching the color change.

Patently ridiculous claims for the purposes of creating drama notwithstanding, no one here (well, certainly not now that housekeeping has serviced the room) claims that heat treating bow bellies isn't a useful tool in the toolkit.

As I have been following this thread and mulling things over in my mind, I am curious about doing a laminated bow of two layers consisting of one raw slice for the back, and another baked in a controlled temp oven for the belly. Zero chance of overtoasting and far more consistent results across the belly. Now, where can I buy a six foot wide oven???

[Deerhunter21]

The experience of Bamboo flyrod builders seems to mirror our experience.   Of course we know bamboo is grass and not wood.

 I wonder if Marc is thinking of Dick Baugh?

 Here's the bamboo tests:
 http://www.powerfibers.com/BAMBOO_IN_THE_LABORATORY.pdf

Yes it was Dick who did the testing. 

I think it's time for Tom to say goodbye

I already don't miss him! 

Now that the housecleaning service has dealt this the matter, shall we get back to work?

To my mind, there are two extremes of heat treatment, both being of zero value. First would be toasting a bow until the entire thickness of the bow has reached the same temp as the belly and the bow is ruined because the back now will not handle the tension. The other would be toasting so rapidly that only the very thinnest surface layer of the limb actually has change, as often signified by the change of color, yielding virtually no measurable change in the behavior of the wood under bend.

How to heat to a consistent depth along the entire belly of the bow without compromising the back of the bow is where the skills part of the equation comes into play. Whatever means you choose, you need to control both time and temperature, with each of the two variables affecting the other in real time! I think having a clock on the bench as well as one of those fancy infrared temperature sensor guns would go a long way to helping someone generate some consistency, but a lot of us are going by keeping a slow count in our heads and watching the color change.

Patently ridiculous claims for the purposes of creating drama notwithstanding, no one here (well, certainly not now that housekeeping has serviced the room) claims that heat treating bow bellies isn't a useful tool in the toolkit.

As I have been following this thread and mulling things over in my mind, I am curious about doing a laminated bow of two layers consisting of one raw slice for the back, and another baked in a controlled temp oven for the belly. Zero chance of overtoasting and far more consistent results across the belly. Now, where can I buy a six foot wide oven???

Might I suggest using billets for the belly? You’d only need a 3’ oven instead of a 6’

[RyanY]

As I have been following this thread and mulling things over in my mind, I am curious about doing a laminated bow of two layers consisting of one raw slice for the back, and another baked in a controlled temp oven for the belly. Zero chance of overtoasting and far more consistent results across the belly. Now, where can I buy a six foot wide oven???

I tried this on my last couple laminated bows but made the bellies too thick and the heat didn’t seem to penetrate enough. I think if you started out with a 3/8” belly piece you could heat the crap out of both sides with a heat gun for similar results.

[PatM]

  I think DC has been dabbling with  fully heat treated belly pieces.  The  two wood bows of   Eurasia used heat treated belly lams.  I'm sure you could improvise an oven of sorts in an outdoor setting  by making a long bed of coals and covering it with a metal box or similar.


 Personally I don't find it hard to just toast the belly of a stave and  get the heat into the stave to a sufficient depth without going through to the back

[Eric Krewson]

Of course very consistent heat treating will yield the best results.

Like all my bowmaking I just do things by what feels good to me, heat treating included, I don't measure much or time myself and often just say "that's good enough".

Works for me, 27 years of experience might come into play as well though.

If Tom is gone it will be a breath of fresh air, I had to bite my tongue to keep from responding in a negative way to his caustic posts.

[meanewood]

I typically use bow woods that benefit from heating like Ash and Elm.
A few years ago, I had a yew sapling seasoned and ready to go.
The problem was that it was thin, (33mm) at the center.
So I decided to make a longbow, 33mm x 27mm at the center with normal taper to the tips.
This created a flat belly, but not enough wood was removed to expose the heartwood except in the final 300mm - 400mm of the limbs.
So I decided to heat treat the sapwood belly to hopefully harden it up, to be able to cope with the compressive forces.
This worked very well and it is a nice shooting bow of 80lbs at 30 in draw.
In fact the heated sapwood became so hard, I had real trouble stamping my usual bowyers mark at the arrow pass point.
I use a leather stamping tool and normally have no issues producing a nice clean mark on hard woods such as Oak, Hawthorn and Yew heartwood.
So I guess most people know Yew sapwood is the best there is for a bows back, even when the rings are severally violated.
I would never have guessed that the sapwood heat treated could transform into a robust, compression resisting belly as well!

[bassman]

Even Osage can benefit from heat treating.

[AndrewS]

In Europe, research is being carried out at various universities on and with "thermowood".
At ETH Zurich, for example, I have found many things on this subject.
That was years ago but there were some very interesting statements about heat treatment of wood and the effects on the wood properties.
- The so-called equilibrium moisture content decreases. This means that microbes and fungi can only decompose the wood much more slowly. This is especially important in wood construction. Untreated pine may last up to 5 years outdoors. As thermowood, pine lasts 15 years and more under these conditions. Ash is offered thermo-treated as a floor for bathrooms....

- The wood becomes harder and lighter (less residual water in the cells) but at the same time more brittle (it is similar with steel). If you make the wood too hot or treat it with too high heat for too long, the wood can be spoiled, if you make too little (in extreme nothing), you will not achieve any change.
One must try to find the optimal compromise between the properties to be achieved and the treatments used.

There is also worldwide evidence that our ancestors used heat / fire to harden wood. The burial sticks and the first spears were not provided with stone tips, but the wood tip was hardened in the fire ....
The posts of pasture fences also often have fire-hardened tips, which moreover also last longer than the non-thermally treated posts....

[Selfbowman]

Interesting Andrew. I think it helps at the 350-400 degrees so I will keep doing it that way. Arvin

[AndrewS]

I have only worked with a hot air gun so far. Even this can be done in very different ways: Low or high temperature setting, distance of the nozzle to the wood and the time interval for how long I temper the wood.

I have tried a lot and sometimes even deliberately worked on the borderline.
In the meantime, I tend to temper more slowly (minimum: 1 hour per limb), not with the maximum temperature (low temperature setting of the hot air gun) and a distance of the hot air gun of about 10 cm from the wood. About 130 - 150° C should result on the wood...(260 - 300° F).
I had best results with elm, hickory, cornus, hazelnut and bamboo.