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.

Let's say that you are making a bookcase out of 3/4" plywood. You
make a dado that is about 5/16" wide on the vertical (side) pieces.
Then you make a tongue on the bottom of your horizontal (shelf) pieces
by setting your tablesaw fence 5/16" away from the nearest edge of the
blade. You will wind up with an offset tongue that will fit
perfectly.

The offset tongue should be made on the bottom face of the shelf so
that the laminations of the shelf ply are loaded in compression,
rather than being under tension.

I usually make thelength of the tongue very slightly shorter than the
depth of the dado, so that the glue has somewhere to go when you clamp
up. By 'very slighty' I mean no more than the thickness of a sheet of
paper.


HTH



Tom Watson
tjwatson1ATcomcastDOTnet
www.home.comcast.net/~tjwatson1