The easiest way to cut large holes, is with a plasma cutter. Make a simple
fixture into which the torch fits nicely, and which has a means of
adjustment for size of hole, and a means of centering. Then merely adjust to
your hole size and cut hole.

Other methods will work, but this is the fastest and simplest way, and is
certainly better if you have to cut more than one or 2 holes.

Gummer
wrote in message
.com...
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.