You might try "treepanning" ( I think that is spelled right !)
just a thought,
Ron
"Michael" wrote in message
.. .
Ryan, i did an almost identical job, 10 pieces in 1" AL, except i was
cutting an arc rather than a complete hole. As others have suggested, i
used a hole saw in the mill at a low speed (not because of theoretical
cutting speeds but because its a bit of a hairy cut to make). There was
enough clearance in the saw to cut the 1" at one go (3.5" hole saw)

Here's a caution for you....Most of the hole saw arbours I could find or
were presented to me by tool store counter help do not hold the saw
rigidly
which it must be to use on the mill. Starrett's A17-12 does hold the saw
rigidly, or make your own. I'm no hole saw expert, but i speculate that
the
most common app for hole saws is blasting through wood on a construction
site, i guess ease of changing blades matters more than a little wobble.

you'll get probably the worst finish ever created in your shop, so buy a
smaller dia hole saw and finish up with a boring head. in my limited
experience, these hole saws are not precision cutters, then again maybe i
bought the wrong one. the set of the teeth seem incorrect leading to a
lot
of rubbing on the outside dia of the saw and the butt weld of the rolled
portion is visibly out of alignment. its only going to be cutting on a
few
teeth so feed was determined by feel. oh well, that's what the boring
head
is for.

hope it helps


"Ryan" wrote in message
...
I have a task which requires boring four 4" holes in .750 plate
aluminum,
with 10 plates in total to do. I have a boring head and / or flycutter,
so
the finish cut will be no problem, it is just going to be a real chore
to
rough them out I suppose. Short of using a jig saw (which I am not
convinced would work too well) what would be the best way to approach
this
task? I would like to use the milling machine for the roughing, so that
I
can rough the hole, then finish bore in 2 steps. Would a trepanning tool
be
the best bet? If so, can someone suggest a particular model, keeping in
mind this job is meanial, therefore tooling costs are a concern.

Thanks in advance,

RB