We had an interesting experience yesterday in the July 8 sack back class. It allowed me to experience something one cannot see. I describe to every visitor here the genius of Windsor joinery. I show them locking tapers. I frequently demonstrate them by lifting a work bench with a leg driven into a tapered hole. I have made various joints and have cut them in half. However, one joint escapes my efforts at show and tell. Those are the stretcher joints. They are in compression. Over-long stretchers push the legs away, rather than trying to hold them together. I cannot show compression. I can only describe how it is accomplsihed
However, yesterday I experienced it in a new way. A guy legging up his chair made a math error. When trimming his legs. (He did not use our mathless method.) As a result, his seat was an inch too low – 16 ½ in. in the front and 16 in. in the back. Of course he was angry with himself and frustrated. I looked at his chair with resignation and reminded him what I had said when demonstrating trimming the legs – there is no fix if you cut too short. We can’t glue the ends of the legs back on.
I pondered the chair a bit, while my camper became increasingly unhappy with himself. I decided on a fix I had never done before. I would cut out all four legs from the seat and ream the tenons out of their sockets. I would reuse the stretcher. I could cut the legs at the stretcher joints if the glue had already set. I grabbed a dozuki and placed the chair upside down and began to saw just above the surface of the seat. As the saw kerf approached ½ the thickness of the leg the blade began bind, enough so I had to work it loose. I finished the leg by cutting from the other side, and it still bound. The same happened on the next two legs. The fourth cut freely.
In the heat of the moment I did not realize why the saw bound. Later, as I pondered the experience I realized that was the pre-load. The stretchers push the legs apart with sufficient force to cause the kerf in hard maple to bind less than ½ way through the cut. The final leg cut without effort, as the pre-load had all been released by cutting the first three legs.
The repair was the chairmaker’s equivalent of finding the Higgs Boson. When scientists make that discovery they won’t be able to see the particle. They’ll only see the result. I know I will never see joints in compression, by I have experienced them and confirmed their effectiveness in a new way. That made the repair worth doing. My camper was ecstatic (and thinks I’m amazing). So, that made it worthwhile too.
The Hampton Summit, the first novel in my series for young teens (and for adults that are young at heart) is now available in both softcover and eBook. http://www.amazon.com/Hampton-Summit-Castleton-Series-Volume/dp/1482731622/ref=sr_1_sc_1?ie=UTF8&qid=1367421699&sr=8-1-spell&keywords=the+hamton+summit The second book in the series The Lost Crew will be launched at the end of this month.
You can follow me on twitter at @castletonseries.
To receive my monthly eLetter of essays about chairs and chairmaking, that are in addition to this blog, join our mailing list by emailing me at firstname.lastname@example.org Help us spread the word about this blog. Tell others.