I prefer hole saws for large round holes because after drilling a center
pilot hole, the drill in a hole saw can generally be replaced with a 1/4"
rod, which almost certainly insures that the hole saw won't go skidding
across the workpiece.
Extended lengths of plain 1/4" rod can make an angled approach fairly
stable, where only one side of the saw starts cutting first.. this works
better for thicker materials where an angled hole or large counterbore is
needed.

I bought some new high quality ones on eBag recently, and the seller had
some in that size range at very reasonable prices (better than local
retail).
They sometimes make oversized holes, so using a smaller size and finishing
to an acccurate hole size may be required.

With flycutters, the full load is only on one side of the cutter's swing,
and things can get exciting very quickly when the cutter grabs and also when
it starts to break thru the back side of the material.

--
WB
..........


"David Lesher" wrote in message
...
A friend asked:

Need to cut a few (=6) 5.5" holes (actually 140mm, but that
is 5.51", so close enough) in 1mm sheet metal (carbon steel, I
think).

2 side by side holes initially in a roughly 20"x17" piece of 1mm
cold rolled steel with one finished side. May need to put holes
in 2 similar pieces of sheet metal later on.

I thought:
HF has a flycutter with a carbide tip...
http://www.harborfreight.com/carbide-tip-adjustable-circle-cutter-68117.html

That, a longer arm & a drill press...
--
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