On 12/12/2012 10:23 AM, Dave wrote:
On Wed, 12 Dec 2012 10:15:44 -0500, Greg Guarino
So there's my next question. My only option for making dadoes is a
router, and I'd love to avoid making extra passes. If I buy a 23/32 bit,
will I be OK? Or is plywood thickness too unpredictable these days?

Plywood thickness is *EXTREMELY* unpredictable these days and has been
for a number of years. You might get lucky and be able to find a
router bit perfectly sized for the plywood on hand, but the chances of
that happening are almost nil.


I knew one of you killjoys were going to say that. So now I suppose
you'll be recommending I get a guide collar for the router or some such.

I have some ideas. Let's see how stupid they are.

My first thought was to use two parallel guides clamped to the work,
spaced apart just far enough so that two passes (one pass touching one
guide, one touching the other) would produce the proper dado width. I
have one of those self-clamping straightedge gizmos, and I have some
non-self-clamping extruded aluminum guides. I'd use some combination.

So next I thought, hey, that'll be a drag to set up 36 times. Maybe I'll
cut a couple of pieces of scrap just the right length to set the span
between the two guides. That would work, I think, but all you guys would
snicker about how clumsy it was. We can't have that, can we?

So now I wonder if I couldn't make a rectangular jig of some sort,
consisting of two wooden guides joined by two other pieces to set the
correct distance. Those pieces would ride along the edges of the work to
be cut, sitting flush with the top. (all of the pieces that will need
these dadoes will be the same width, probably 12")On the first cut, the
"joining" pieces would themselves receive a dado groove, which I could
then use to line up each new dado to be cut in the work pieces.

I think this would work, and could be easily clamped to each new
position. But I worry that my abilities may not allow me to produce a
jig as square and straight as would be needed.

I'm also wondering if I could get away with dadoing a pair of "mating"
uprights in one pass by lining them up next to each other. That way the
dadoes would be sure to line up on both sides of each shelf, but it
would mean reaching farther with the router too, and would make for a
longer jig, more prone to be out of square.