"Jon Anderson" wrote in message
...
On 4/06/2016 12:31 AM, Ed Huntress wrote:
If it's worth the tooling investment, there are some combination
bits
that will drill the hole and then ream it in one operation. Or,
there
are multi-lead drill bits that drill a hole that's closer to being
round.
We have some of the multi-step single lip drills. They don't do a
great job of starting a hole in SS, but so long as material
thickness is equal or less than the step length, they do a good job.
Mostly used out in the plant though, in hand drills.
I'm trying to get approval to purchase a quality bench mounted
punch, something that'll do up to maybe 20mm in 2mm SS. We shouldn't
be trying to drill 20mm holes in sheetmetal...
Jon
Have you considered Greenlee punches? Unless you need to drill an
initial pilot hole they leave no metal chips in electrical boxes, and
unlike a punch press have no throat depth limit and work fine on site
to modify sheet metal control boxes. The cutting edge is a flat
surface you can resharpen on a belt sander.
http://www.electriciantalk.com/f2/kn...rpening-14571/
I used a hydraulic set to punch conduit holes in "JIC" control boxes
when building industrial equipment.
http://www.greenlee.com/catalog/Knoc...d-Kits?ps=1000
You need a third hand to support the heavy pump. The ball bearing
studs were much easier to position and often worth the extra operating
effort. At home I use a platform stacker like this as an assistant to
help hold such stuff.
http://www.digitalbuyer.com/wesco-ll...FYFahgodtfIFlw
I got it for $10 at an auction. The hydraulics are bad so a lever
chain hoist operates it. As a positioner the lever hoist which I can
reach from all around it is better than the foot pump.
I've used one of these at a later job.
http://www.roperwhitney.com/bench-deep-throat.html
The adjustable die shoe makes changing sizes enough of a nuisance that
I left it at 1/4" and opened up holes with a step drill.
I have these two at home.
http://www.roperwhitney.com/portable-light-duty.html
The throat depth is adequate only for small electronics. If possible I
use the lighter one because the heavier is awkward to align by feel on
a punched dimple.
--jsw