Steam or Heat Gun

[Phil Rees]

I'd like to call upon the collective wisdom of the members for advice if I may.
I'm planning on making a Persian / Assyrian style hybrid bow  (circa 900 B.C.) and I need to shape the limbs over a former. I've really have two choices;
 1. is to dry heat the limb with a heat gun and clamp the bow to the former...or
 2. Steam heat the limb in a custom made steam chamber and then clamp the limb to the former.
What I'm asking is "are there any benefits in using one method over the other". I guess I'm looking for the method that will give me the greatest flexibility/plasticity in the wood and minimise the clamping force and also give the best "set" of the limb shape on removal from the former. The woods I'm intending to use are Sycamore and Lime wood.
Your suggestions and experiences would be very much appreciated.
Thank you in anticipation

H.F.

[Del the cat]

Short answer:- I don't think it makes any difference, whatever is easies/cheapest for you.
Longer answer:-
In my view steam is more controllable and quicker, e.g. The whole piece will get upto 100C at the same time (I usually allow 30 mins, but a thin core piece will only take 15-20)
It's easy to build a steam chest, I lashed up some insulation board (the foam stuff with a thin aluminium layer either side) with duct tape and it's done the job for about 3 years! It's easy to punch holes in it for limbs to go in. I use a steam wallpaper stripper to make the steam (they are v cheap and give 30 mins steam no prob).
If ind dry heat a bit of a fiddle as you are waving the heat gun about, or moving the jig all the time.
With steaming you have to get it all absolutely ready so you are onto the clams in a matter of seconds (unless you improvise a steam chest around the former, which I've done before now).
Del

[George Tsoukalas]

Just don't use dry heat on green wood. Jawge

[mox1968]

steam to shape to your former then a bit of dry heat here and there to tweak it when it comes out of former.

[n2huntn]

For me steam is faster and easier for most woods, some respond better than others.Looking forward to seeing your work.
Jeff

[Phil Rees]

First of all, thank you all for taking the time to respond to my question.
We seem to be coming to a consensus that steam forming is the prefered method by bowyers and as Mox 1968 said, use the heat gun for "tweaking".
So I guess my next question is about drying time. Do I just allow the formed limbs to dry naturally or could/should I apply gentle heat?

Once again many thanks in anticipation

H.F.

[Del the cat]

Impatience is my big sin.
I've had 'em move on me when I've only given 'em 24-48 hours, so I recently asked the same question, one of the guys here suggested leaving it clamped up for 5days which seemed to work on the last job I did.
Better safe than sorry, you can always be roughing out the next bow while you are waiting (Or you could ask the wife for some chores )
Del

[JackCrafty]

Seems like you'll need to bend the wood quite a bit for that type of bow.  Sycamore steam bends better than Lime wood, but it is not the best wood for steaming by any means.  Also, I don't think dry heat will get you very far with these woods.

You might try switching to oak or ash, or at least experiment with these woods.  My two cents.   

[eflanders]

Recovery time depends on the thickness of the material being formed, the relative humidity in the air and the moisture content of the wood prior to treating with steam or dry heat.  Rule number one is not to rush or try to force it to dry or remoisturize.  Rule two is not to stress the treated material until it has returned to the proper moisture content.  Rule number three is to use dry heat for dried wood and use steam heat for green wood.
  So, how do you know if it's the right time?  Use the weight method.  Weigh the workpiece before heat-treating it.   Weigh it again after it has cooled to room temperature.  There will be a weight difference.  Once the weights equalize, (usually days later) you can begin to stress the wood.  If you follow the above three rules, you will avoid excessive string follow, checks or cracks and or explosions. 
  As an added note, when heat treating wood regardless of method, it's the core temperature of the material that makes and allows for a permanent change in shape.  If the material core doesn't get hot enough, the material will try to return to it's former (as grown) shape. 
  For safety sake, make sure that if you use steam, that you do not allow pressure to build up in the steam chamber and let the steam and moisture trickle out.  You do not need to seal the ends of the steam chamber for the heat-treat process to work.  It's all about time and temperature.  Pressure treating is not heat treating! 

[Phil Rees]

eflanders...
Thanks for the extensive reply, your comments make perfect sense and I'll follow your suggestions especially the piece about weight before and after steaming.... many thanks for that.

Seems like you'll need to bend the wood quite a bit for that type of bow.  Sycamore steam bends better than Lime wood, but it is not the best wood for steaming by any means.  Also, I don't think dry heat will get you very far with these woods.

You might try switching to oak or ash, or at least experiment with these woods.  My two cents.  

Thanks for your 2cents Jack .. because I'm  trying to be as authentic as possible, my wood choices are a little limited to the woods found in that area. I know there are pre Christian era bows of Sycamore and Lime but I could consider Walnut and Acacia as well

So... many thanks for your input
H.F.

[dragonman]

Horace, heres my 2 cents, for what it is worth.... first cent.... Steam bending is more wood freindly,water makes things softer, boiling is even better(from cold)
                                                                      second...... sycamore and lime aren't up to the job, thats a seriously reflexed design that requires stronger wood

[Phil Rees]

Horace, heres my 2 cents, for what it is worth.... first cent.... Steam bending is more wood freindly,water makes things softer, boiling is even better(from cold)
                                                                      second...... sycamore and lime aren't up to the job, thats a seriously reflexed design that requires stronger wood

 Dragonman     Boiling ... tell me more ...

[eflanders]

  Boiling will work like steam or dry heat if you boil it long enough to raise the core temperture of the material.  In my opinion and experience you can steam a piece in a much quicker time than you can boil it.  Remember the key is to get the core temperature of the material up to about 110' F as a minimum. 
  Pros & Cons:  Steam or boiling the material will not discolor the wood like dry heat will.  It will take longer for the material to dry to the relative humidity of your environment if it is boiled rather than steamed.  Dry heat will take the shortest time to return to the relative humidity of the environment.  When boiling or steaming the wood it must be formed & clamped immediately upon removal from the steam box or water bath.   When using dry heat, you form the material as you move along the work piece.  If you use Marc St. Louis's dry heat method, you can also add resin or tung oil to the material as you work to aid as a wood preservative.

[dragonman]

Horace, the main problem with boiling is finding a suitable container. Some people even soak the wood in water for a week before boiling then boil for 2hours. This ensures all the cells of the wood right through to the centre are saturated with water, this caused the least damage to the structue of the wood when bending. This is the optimum... for most purposes steaming for an hour is sufficient for most woods,  I believe, Provided wood isnt too thick

[eflanders]

Horace, the main problem with boiling is finding a suitable container. Some people even soak the wood in water for a week before boiling then boil for 2hours. This ensures all the cells of the wood right through to the centre are saturated with water, this caused the least damage to the structue of the wood when bending. This is the optimum... for most purposes steaming for an hour is sufficient for most woods,  I believe, Provided wood isnt too thick

While I agree that finding a suitable container is an issue ( a rain gutter works as does a closeable piece of pipe), I disagree with the statement that "soaking the wood ensures that the wood cells are saturated with water".  The wood cells are filled with air and this is what allows wood to float.  It takes a very long time to saturate the cells with water (as in weeks and months).  However, with steam heat, it takes a much shorter time (as in hours).  A standard that many wood heat treaters use is one hour of steam per inch of wood.  Which by the way does agree with the time frame listed in the above quote for most bowyers.