If you can get to it, mark the slot and hog out some of the midsection
Forstner bits on a drill press. Then (with suitable guides clamped
to the work) route full-depth with a smaller bit (maybe 1/2").
It's easier to get the bit into the cut if you dont have to plunge-cut
(and you can use non-spiral bits), it's easier on the ears to remove
the bulk of the wood with a Forstner bit, and the heat buildup (and
wear) on the expensive router bit is minimized if you just clean up
the edges with it.
I wonder the length of your board. A dado blade in the table saw will
work and is accurate but you will need to chisel out the end(s).
Another method that works well... Clamp on a straight-edge and make a
hardwood strip that is taped to the straight edge. Make the first
pass with a 1/2" , remove the strip, make the second pass. You may
need 3 or 4 test tries to get the groove width you need. After the
gauge strip is correct, the setup is repeatable.
A router sled jig is another consideration, good or not depending on
I have not seen a 3/4" straight router bit, but that sounds hefty
(probably pricey), and you may need better at a slower speed.
routing to that depth is _no_ problem, assuming you've got an 'adequate' router.
_I_ would use a narrower bit, and do two passes -- that way I can guarantee
an exact fit for 'whatever' thickness the nominal 3/4" ply is. I've had some
that would _not_ fit in an exact 3/4" slot and others that were loosey-goosey
in a 23/32nds slot.
The type/class of the plywood, the manufacturer, the humidity it's been exposed
to, can all make a difference. And they're all -guaranteed- to be in the
direction that you'd rather -not- have them go. <wry grin>
This is especially important since you've ruled out the optimum solution of
cutting a slot with a Freud 60-tooth blade. Which, as reported in another
thread herein -- according to Freud's own advertising -- "always cuts to the
correct length." :)
On Sun, 17 Jan 2010 19:53:53 -0700, Robert Bonomi wrote
I've gone the router route ;^)
Problem with a dado set is you must make sure the wood is _firmly_ forced
against the table or the resulting bump in the bottom of the groove will
throw everything off. Also consider cutting more than a foot into the center
of a board (side shelf supports). Either you need a really long miter gauge
or a good panel sled setup.
Good guide rail, and do it in two full-depth plunges, one for each
If you've got a really good guide rail, you could do it in one pass
(for 1/4" depth) or multi-depth passes, cutting both sides
simultaneously. That's a hateful process though, as the forces are
pushing you both ways simultaneously, so are far harder to control.
Don't try to get to the thickness of the plywood.
Cut a rabbet to a "known" thickness(1/2" is good)
and then route a slot using a 1/2" bit.
Using this method, you can really get very close
and not worry about weird sized plywood.
Actually, I would make my dado and sneak up with
You can do this with a table saw or a router table.
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.