Wednesday, March 21, 2007

The Road to Bending pt.2


The first bends I made were as an apprentice cabinet maker. I learned to kerf substrates to make them flexible and then laminate them. Later I would make bent laminations with thin strips. That's a lot of work! Don't get me wrong, these techniques have their place and in cabinet work, create great freedom. When I go to prepare my stock for bending, I like to think that I am still doing bent laminations, only now instead of strips of wood, I use years of growth.
I choose fast growth logs for my bends. A careful examination of the endgrain of a ring porous wood will reveal that the early growth (the porous "grainy" wood) is always about the same size. The variation comes in the dense late growth. In bad years, the growth of the late wood may be no more than the early yielding a ratio that is 50/50. I prefer for the late wood to be much greater in proportion. Think about it, which chair would you rather see a 220lb man plunk down it, one made of porous early wood or dense late wood?
Once I have split my stock, I proceed to follow the fiber with my drawknife and shape the piece. This is where you will actually be deciding if your bend will succeed (I am referring to the extreme bends needed for chairs, more subtle bends can probably succeed with planed wood). I never use a handplane to size my bends, the goal is to follow the fibers, even if they bend, NOT to flatten the piece. Once I've followed the fibers on a reference face, I can mark the thickness and rest assured that when I shave the other side, I will be following the fiber line when I get to my mark. It is vital to let the drawknife do its job. I will go into this more later (it's probably the single most important thing to comprehend in making a strong chair, thanx Mr. Sawyer) I always use my bevel up drawknife for this kind of work. I find that it splits the wood away, as opposed to the bevel down which seems to encourage me to try to exert control. Once the knife is in the cut, just pull (skewing and slicing of course!) and let the knife find the fiber line. The beauty of green wood is that with a little practice, it will peel like a banana. The photo is of the dreaded arm bend on a continuous arm. You can see the growth rings where it steps down in size and then the single year that is the outer surface of the bend. I simply try to leave no place for it to fracture, just like a bent lamination. Equal thickness is also vital. The tension of the bend will head immediately to any thin spots and cause a kink if not a break. I always try to have my riskier bends take place so that the outer and inner part of the bend are in the tangential plane. If I told you to take off your belt and wrap it around your hand, you would probably do it by placing the broad face against your hand and wrapping it. To me, this is also the best way to bend the wood (the growth rings are the belt here) without creating undue distortion. I may very well be off on this and I know it can be argued!
Basically, my goal in stock preparation is to create a mini tree, with the surfaces running perfectly parallel to the fibers.
Next, my steamer

2 comments:

Anonymous said...

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Marc in Luxembourg

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