On Thu, 14 Jul 2005 08:23:48 -0700, Smitty
wrote:



When I get to my panel, which isn't going to be soon, I'll probably do
it on the mill. But for those who don't have access to a machine shop, I
wonder why you're talking about hole saws and fly cutters. Don't the
Greenlee type punches work pretty well? You only need a small pilot hole
and a couple of wrenches.

They cut a pretty good hole with cleaner edges than the hole saw and
are physically easier to use than a fly-cutter and safer than both,
but they do have some short comings.

Good hole saws can do a reasonably good job if the piece is firmly
clamped, the drill press, or mill is running very slow, and you use a
good cutting lubricant. Apply a very light pressure when starting the
cut although the saw will probably still grab. You should be able to
cut a nice round hole with out the saw wandering. The edges of the
hole will be a tad rough though.

With a fly-cutter, firm clamping is equally important. In addition
the bit needs to be properly shaped and sharpened as well as set at
the proper angle.

BTW, The quality of the hole with either the hole saw or fly cutter
depends highly on how well the piece is clamped in addition to the
safety issue.

The punches have to be in good shape other wise the edges of the hole
(usually by the points) can roll in and they oft times have a small
lip on the inside. This *usually* isn't much of a problem, however
the pilot hole needs to be a slip fit for the bolt and it needs to be
round if you expect close tolerances in positioning. That brings me
to the next one which is the larger punches. They require a pilot
hole punched with a smaller punch which needs to be a good fit to the
larger bolt. This can either give the user a chance to even out any
misplacement with the first hole, or accidentally add the
displacements to the point of where they are noticeably out-of-line.
I'd probably use a lot of Aluminum sigh and I've punched a *lot* of
holes using both the mechanical and hydraulic operated ones.

One final point. This type of punch is *EXPENSIVE*. Good quality
ones large enough for instruments will run well over a $100 and you
need a smaller one for the pilot. Over all it'd probably take about 5
different punches to do a panel with the punches ranging from about
$65 to $150 if they are real Greenlee punches. (Now if you know some
one with a set that's in good shape... G)

I was going to purchase a set and came away with a real case of
"sticker shock". I'm still keeping my eyes open for a used set in
good condition though.

Having said all of that, like any of the methods, skill plays a part
from the user and I've seen some very nice panels cut using all three
methods and I've seen some of the rejects too. :-))

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com