On 3/28/2013 7:06 PM, woodchucker wrote:
As far as the curve, it's trial and error, you want the pressure to keep
from picking up in the middle.

I just remembered something. I was putting an edge around a desktop a
couple of years ago, back before I had all of my current woodworking
savvy. The desktop is pretty large; 72" by 30" if memory serves. I
had not yet discovered pocket screws (along with many other useful
techniques). I decided to use glue, dowels and clamps.

I had only two clamps long enough for the long dimension. Adding to the
problem, the piece of oak 1x2 I used for one end piece was bowed a bit.
When I applied the two clamps I still had a small gap in the middle. I
decided to take another piece of 1x2 oak and put it in as a "caul", a
word and concept I had not yet heard of.

I have a reasonably intuitive grasp of physics, but somehow it didn't
occur to me to put the "caul" on edge for greater rigidity. Or to use
something thicker. In the heat of the (glue drying) moment, I grabbed
for the first thing at hand.

The thin pseudo-caul helped a little, but there still wasn't enough
pressure in the middle. I grabbed a small piece of very thin plywood,
maybe 3/16", and inserted it between my "caul" and the middle section of
the edging. Then I cranked down the clamps tight, bending the "caul".
That did it.

I didn't occur to me until now that I had in effect made a crude
"stepped" version of your curved caul; a piece that protruded more in
the middle than at the ends.

I have since been advised that there were any number of better and
easier ways to accomplish the whole task, but it's funny that I ended up
reinventing the wheel to solve a problem in a time-sensitive moment.