On Tue, 24 Jan 2006 19:59:56 GMT, noonenparticular wrote:
Big in the sense of the boards (timbers?) involved.

I'm trying to edge join the two boards for my bench top. Each board is 80"
x 3 1/2" x 7". They're big and I need to join the 3 1/2" edges.

Here's what I've done.
- Got the faces flat and square by using long 4" wide strips of plywood
screwed to the sides to form a sled. Ran it through the planer to flatten a
face, then removed the strips, flipped the board and flattened the opposite
face.
- planed one rough edge down to mostly flat (so the bit wouldn't have to
take a big bite in the next step) then laid the board on its face, screwed
one of the straightedges to the face (actually the bottom face so the screw
holes will never show) then used a pattern cutting bit (bearing on the top)
to true half the thickness of the edge.
- Removed the strip, flipped the board and changed to a bearing on the tip
bit in the router and rode that bearing against the edge created in the
previous step.
- I did this to each of the two boards thinking that I would get a nice
mating surface. What resulted was not bad, but not the tightness that I was
expecting. Would like to get these tighter and some solutions (like adding
clamp pressure to draw the boards together during glue up) simply won't work
given the size of the boards.

Any ideas?

By the way, I'm going to use a full length 3/4" plywood spling during glue
up. Also, the gap on the edge at it's max is about 1/32, although most
spots are less or touch flush.

So the plywood "straightedge" wasn't so straight.

You might do better using a tablesaw. Screw the plywood strip so it overhangs
the opposite edge, and bear against the TS fence with it. This way, the impact
of small variations in the plywood will be reduced by the long fence.

--
Art