Replies

1. 
   joinerswork | Aug 05, 2010 08:18am | #1

   stan,

   You've chosen a difficult wood for your first attempt at bending.

   Mahogany is typically listed as difficult to impossible in listings of woods for bending.  In bending something as thick as 4/4, you are adding to the challenge.  I have successfully bent thin mahogany stock, but have not tried thicker stuff.  I was able to have some success by immersing the mat'l in boiling water, and by backing up the bend with a metal band that kept splitting to a minimum.  Using heat alone is a technique that I've only seen used on thin mat'l, like shaker boxes or guitar sides.

   An add'l challenge, once you have the bend made, is whether it will retain its shape  (springback).  I'd not be too optomistic unless the bend is restrained somehow in its final location.

   Have you considered a lamination of several thin (1/8' or so) strips of mahogany, glued together over a form?  You might have less heartburn if you can do this.

   Ray

2. 
   hammer1 | Aug 05, 2010 09:14am | #2

   Don't know who told you heat alone allows bending but the info is not correct. The fibers in the wood have to both stretch and compress when bending. Heat will give the fibers some elasticity but its the moisture in steam that allows it to compress. The moisture also helps the fibers stretch without breaking apart. When you pull a piece out of the steam box, you have seconds to get it in the bending form and clamped.

   You will have the best advantage bending wood if its green and riven, meaning split from the log along the grain, not sawn. Boat builders bend some huge pieces of lumber but they don't start with kiln dried boards sawn from the log. If your material is KD sawn, you would be better to laminate it. You may have success steaming 4/4 but you will likely break a lot of pieces to get one.

3. 
   hammer1 | Aug 06, 2010 09:48am | #3

   You are looking to make a 90 degree bend in KD sawn lumber, that's a different animal. Toss a piece in the oven and give it a try.

4. 
   KeithNewton | Aug 09, 2010 10:28pm | #4

   Steam Bending mahogany.

   If mahogany was my wood choice, I would use the laminating process. 

   As for another reason not to use dry heat. If you have to heat it above 210º long enough to reach that temperature all of the way to the middle, you will be cooking it down to oven dry / 0% MC. Since you will probably be doing that too fast, it would likely check from drying too fast on the surface before the middle gives up its moisture. 

   Then if you managed to succeed in making the desired bend, you would need to expect the part to swell as it gained moisture coming back up to EMC. 

   Conversely, when you steam wood, it will likely come out of the chamber around 18 ~ 20% MC, even if it went in a lot drier. For this reason, it is best to use air dried wood around that MC, to avoid sudden gradient  changes.