What size hole saw do I use?

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


snip

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.

I have bought several Greenlee hole punches from e-bay relatively
cheaply. My 3 1/8" cost me $100 plus shipping. Two things must be taken
into consideration: first most are used and need to be sharpened and
second conduit punches run 3/8" larger than the given size, e.g. a 2"
conduit punch is 2 3/8" actual. Sharpening is easy with either a medium
grit wheel (you use the side of the wheel) or a good, flat medium grit
whet stone. Punches listed as radio chassis punches are acual size.

Dan, U.S. Air Force, retired