On May 23, 7:36 pm, Tom Watson wrote:
On Fri, 23 May 2008 16:35:46 -0600, "asmurff"
wrote:

I'm going to cut a dado in 2 pieces of plywood to put a third piece of
plywood into on the tool stand I'm building. Is 1/32" wider than the plywood
thickness enough.

Plywood varies in thickness, not just from sheet to sheet, but in
different places on a single sheet.

Better quality cabinet grade plywood varies less but still varies.

What I have come to do is to not use dadoes that are the full
thickness of the ply. I usually make a dado that is in width from a
third to a half of the nominal thickness of the ply. Then I cut a
tongue in the other piece to match that width.

This takes the variation in thickness out of play.

I don't think that takes the variation out of play, it just hides it
somewhat. Generally you'll see plywood that is a bit wavy in
thickness, but rarely does it taper. Cutting a tongue like you
suggest will remove the waviness from one side of the board and the
wavy side, being the tongue on the bottom, is generally more hidden.
That technique doesn't address the waviness of the plywood sides. The
perfectly straight rabbet cut on the shelf will be on the top and
you'll still see the waviness that's in the uprights.

R