My consternation with getting a another ~7" hole in 3/8" aluminum
plate should be satisfied after this question.

Several helpful people have suggested that I use a template and
carbide router with guide bearing to cut the hole.

Well, in my mind, I can see that the template could either be on
either side of the plate. If on top, I would need a template much
larger than 7" so as to allow the router plate's edge to be in contact
with the template. It would necessitate my drilling a hole to get
started so that the bearing would fit through. Although, after
drilling the hole, the bearing wouldn't contact anything. May in the
case of the template being on top, I don't need a guide bearing on the
router bit.

If the template is on the bottom, I would cut only a 7" hole in the
template and also cut a starting hole in the aluminum all the way
through so that the router's guide bearing will contact the template.

So which should I do?

Thanks everyone for all of the input.

Soon, I will be asking about how to cut a small taper on a 7/8" shaft
with the lathe's compound rest.


You can buy (or make) a set of bit bushings for the router which screw
into the base of the router and basically create a "tube" around the
bit. They can be selected to permit various size "gaps" between the
bit and the inside of the tubular bushing. After the bushing is in
place in the base of the router (sticking down below the base of the
router), the bit is inserted, and the depth is set. The template hole
can be only 1/8" or 1/4" larger than the desired hole in the material.
The starting hole is drilled, the bit of the router is placed down
through the starting hole and the *outside* of the bushing surrounding
the bit is held against the template edge as you go in a circle to cut
out the desired 7" disk. This way, a straight bit is used *without*
any guide bearings.
Hope this helps.
Ken.