Wednesday, January 19, 2011

Two Ideas, One Great and One Questionable

I received an email from Paul Linden with this link to Drew Langsners blog that shows an idea so simple, yet smart, that I am not surprised that it came from Japan.


I've always wanted an indoor brake for smaller work, especially on days like Monday, when it was extremely cold and we had two chairs worth of parts to bust out. So, I cut a few kerfs in a large chunk of wood left over from the barn and had an instant brake!  When it's not in use, it becomes a low bench for sitting by the fire, not a bad alternative use. Thanks Paul and Drew for the enlightenment.

Now, it's into the breach. A recent commenter asked about a previously mentioned topic of the "preload" that some folks put into their undercarraige. I said that I'd address it later, but I suppose I let it go, and maybe for good reason. This is one of those contentious techniques that seems to bring out the partisan in folks, so I am loathe to go there.

For those who don't know, the idea is this. Add some nominal length to your stretchers and the legs will be under an outward tension that will resist spreading in use. Sounds fine, and I'm sure that in most cases, it doesn't hurt to do it. So why don't I do it?

It comes down the question, "What holds the chair together?" I think well sized joints with the proper moisture content hold together chairs. For instance, would you ever put an unglued,  undersized tenon in a mortise under "preload" and expect the legs not to spread when sat upon? Taking it just a hair further, ask yourself, what does wood do when stressed into a position? It tends to relax and remember the shape. So whatever benefit that you might gain from the "preload" is either minor or short lived.

"So what?" you might ask, if it doesn't cause problems, why not use it. Well, I'm not convinced that it doesn't cause problems. One problem that I see is the possibility that when the joints are as tight as they should be, that the amount that the "preload" misaligns the parts might be enough to cause one or more joints to not seat properly.
But the greater problem that I see stems from our common humanity, which in my experience says that relying on "preload" might become an excuse for some sloppy joinery habits. Misalignment can temporarily mask a baggy joint. I've found that insuring the proper sizing and moisture content of a tenon takes more care than adding a quarter inch to the stretcher length. There are plenty of ladderback chairs that have stood the test of time without the benefit of glue, just good joinery. So for me, that is the benchmark and where I choose to put my energy and reliance.

So there's it is, you might disagree, you might not care (which is basically my take), but more importantly, if you are like me, you make chairs to embrace a quiet and humbling experience where the process is the pleasure and the rigid world of flat and square gives way to curves and most importantly, flexibility.


Anonymous said...

Thanks for the quick reply. I forgot to mention in my email how much I liked the 79 degree block for drilling the legs and stretchers.

Anonymous said...

Thanks Peter for commenting on this topic of the "preload". I tended to think along your line that it really just made your feel like an added guarantee of future durability but actually tended to just make you feel better about doing poor joinery. As a novice I was confused as to whether professional chair makers actually bothered. I personally didn't want to. To me it seemed to encourage error. Anyway, thanks for the post.


Peter Galbert said...

I'm glad that it helped!

Anonymous said...

I was trying to split some wood yesterday, it's England and was pouring with rain and was interested to find your indoor break whick looked a lot better than my attempts at using the vice. anyway a thought struck me watching you demonstrate controlling splitting and that is why are froes made with just one handle? I just thought one at each end of the blade would give you a lot of control.

Peter Galbert said...

Interesting idea, I never thought about it. I always use my free hand to contact the wood, but it might be a notion to consider!