Replies

1. 
   ring | May 13, 2009 07:43am | #1

   I'm assuming that this is not a production run that would justify the expense of a 3D mold with hydraulics.

   If you've got a steam chamber that will accomodate the piece, make it in 2 stages - first the top bend, and then after that's set, steam and bend the lower arm parts.

   If your sense is that it almost works but it's just taking too long, you need to change the way you're applying pressure. Standard clamps? Maybe you could change the set-up to use long continuous threaded bars of vise mechanisms to get fast pressure. And 3 people working together.

   David Ring

   http://www.touchwood.co.il/?lang=e&id=1

1. 
   killenwood | May 13, 2009 08:03am | #2

   Ring, appreciate the ideas..... especially taking it in two stages.

   We're having a hard time figuring out the fast clamping method to start the bend and get the upper thick portion down to the form from the straight.

   You are right, this is a one-time chair by a student in my class. No production here.

   Tim

2. 
   saschafer | May 13, 2009 04:01pm | #3

   Tim,

   You work exclusively in SketchUp, right? I would have thought that bending things was trivial in SketchUp. ;-)

   There's a video with Michael Fortune from a couple years back that shows how he pre-bends a steamed piece in two directions to limber it up, so to speak, before attaching it to the bending form in its final orientation. That technique might be useful here. Apart from that, I think the two-step bend is the way to go.

   -Steve

    

3. 
   joinerswork | May 13, 2009 04:37pm | #4

   Killen,

   The trick to steam bending is to make haste, slowly.  That is, have all your stuff at hand, and plenty of help available, rehearse what you will be doing, with what.  The bends must be made expeditiously, but smoothly-- sudden jerky moves will invite a crack.  The motion must allow the fibers time to slip and slide along one another, yet take place while the wood is still plastic.

   I'd suggest making the transition a gradual decrease in thickness rather than a step, as you've drawn it.  An inside corner is a great place for a split to start.  You'll want the straightest grain possible.  Something riven (split) from a log is best, otherwise select for the straightest grain you can find.  Grain runout on a corner of the stock is a place for a split to start. Orienting the growth rings with one of the faces of the stock will improve your success rate,  and putting them so that the rings are parallel with the direction of the tightest of your bends (so the "layers" of wood can slide past one another) will help too. Rift grain makes bending more of a hassle, I believe.

   In making snowshoes, with a very tight bend at the toe, we found it helpful to clamp a length of metal strapping across the outside of the tightest portion of the bend, using thin blocks to minimise bruising, and a couple pair of vice-grip pliers.  The center of the bend was strapped, the stock bent round its form, secured, then the long "legs" bent down (to form the upward bent toes) and in, wedges being driven alongside the bends onto the form to hold things in place as we went along.

   Edit to add: We had a stout block at the apex of the toes' curve with a "hook" on it to grab the toe and hold it in place at its center as we bent it to its shape, and keep it against the form as we bent the "legs" down.

   Ray

   
   

   ---

   Edited 5/13/2009 9:42 am ET by joinerswork

   
1. 
   killenwood | May 14, 2009 08:16pm | #5

   Thank you all for the helpful specific information.....

   Regarding the SketchUp comment.... I find these bends to be a challenge even in the computer. I enjoy, however making the "real product".

   Tim