On 12/15/12 9:30 AM, Greg Guarino wrote:
On Dec 14, 3:35 pm, Swingman wrote:
On 12/14/2012 2:03 PM, Greg Guarino wrote:
On 12/14/2012 1:54 PM, Peter Bennett wrote:
On Thu, 13 Dec 2012 21:38:15 -0600, -MIKE-
wrote:
On 12/13/12 8:19 PM, Peter Bennett wrote:
My router dado jig doesn't need guide bushings or a top bearing bit -
it guides the router base.
each side of the guide consists of two pieces - a wide piece of 1/4"
plywood that the router rides on, and a (straight!) piece of 1/2"
plywood, or similar piece of solid wood glued on top.
Before the first use, run the router along the jig with the base
against the 1/2" board, so the router bit can trim the 1/4" plywood to
the correct size.
The jigs we're discussing adjust for the thickness of the board that
will go into the dado.
If I understand correctly, all your jig does is allow you to line up
perfectly with a marked line, like a circular saw rip guide.
No - my dado jig uses two pieces as described, joined similarly to the
Woodwhisperer's dado jig, but it uses the router base as the guide,
rather than requiring a guide bushing or a bearing on the bit. (maybe
I should take a picture of it, and post it somewhere...)
Now that sounds like the idea I had. The two guides are separated by a
distance equal to the diameter of the router base plus the thickness of
the stock to go in the dado, right? The router base rides along one
guide first, then the other? I figured if I did this the first pass
would cut a dado in the pieces that join the two guides together,
thereby giving me registration marks to line up the cut with. The
pattern bit idea sounds even more foolproof though, at least to my
untutored ear.
All basically the same principle ... the edge of the router plate in
this one takes the place of the bearing in the top bearing bit method,
or the edge of the guide bushing in the other method.
IMO, the problem with the all the router methods boils down to the use
of a wooden jig, which is prone to the dimensional instability of wood;
and/or the concentricity of a router plate; either with the potential to
effect accuracy over time.
How often do we get to use the word "concentricity" in a sentence?
Google groups even puts a squiggly line under it. 
I don't have the table saw option. But I was wondering about both of
those potential problems too. I think that the small imperfection
would probably not be out of place when compared with my general level
of work (sigh), but I'd be perfectly happy to avoid it. I wonder if I
couldn't make the edges that the bearing rides on out of something
more "dimensionally stable"; maybe strips of aluminum set into slots
(or rabbets) in both guide edges, just a little proud of the wood
edge.
I think, as others have also suggested, the best bet is a bearing bit
with a plywood jig.
A strip of hardwood for the nearing to ride against insures a smoother
surface. This type of jig only needs to be dimensionally stable from the
time you clamp it down until the time your cut the dadoes. :-)
Of course there's always the option of using a couple of these guide
clamps with a bearing bit....
http://www.rockler.com/product.cfm?page=25134
Use the first one to clamp along a marked line on one side of the dado,
using squaring attachment blocks. Use the second one to "sandwich" the
material that will go into the dado, clamping against the squaring
blocks of the first guide clamp. Cut the dadoes, running the router
along the flat tops of both guide clamps.
--
-MIKE-
"Playing is not something I do at night, it's my function in life"
--Elvin Jones (1927-2004)
--
http://mikedrums.com
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