Tuesday, May 13, 2008

Mind the Arc

I built this cabinet in 2005, and last year I noticed that the gap in between the two doors was no longer as even as they had been (they were never perfect, but close). The top of the gap was a little thinner than the bottom. Or so it seemed. I ignored it at first, chalking it up to sloppy construction. But it got worse. After a few days, the gap at the top was less than a 1/8" and the gap at the bottom was 3/8".

(insert little girl scream)

Here's what happened. When I built the carcase, I didn't pay attention to the arc of the endgrain. The second photo, taken from beneath the cabinet, shows the endgrain (on the tails). You can see that the crown of the arc is arching away from the carcase . What happens with a flatsawn board like this is the grain essentially wants to straighten itself out. So, the last tail in between the carcase and the door started to pull away from the last pin, effectively taking the bottom of the door with it. What I thought was an indestructible joint was failing...badly.

So I added glue, clamped it up, and drove a screw through the pin.

A better way to build a carcase or box is to orient the crown of the arcs toward the box. So, when the grain tries to straighten itself out, the pressure will be into rather than away from the joints.

I haven't had the nerve to check the other side of the carcase, but if it does happen to the other board, I'll know not to hyperventilate.