On Sun, 29 Jan 2012 20:37:15 -0600, Louis Ohland wrote:

Folks, I'm looking at boring a 5/8 inch diameter by 5 inch long hole
through 4140 PH, so I can make a barrel stub for my TC Contender.

From initial comments, I'll need carbide to do this... BUT... pure
carbide needs rigid setup, which I don't believe my Grizzly G9972Z lathe
has. Once I punch through a 1/2" hole, then I can whip out my CCMT
boring bar and do it.

Will HSS or cobalt drills get er done?

Heat treating would add more cost to this than it's worth. Really, if I
could find a clapped-out Contender barrel, I'd saw the barrel off, bore
it, and stub it. But barrels are not cheap on ebuy...

Some advise I got on this sort of thing matches well with my own
experience:

You can work hardened 4140 just fine with HSS or cobalt, because 4140
can't get all that hard (it's only 0.4% carbon, after all). But it dulls
the tools quickly.

For a _production_ environment, where floor space is money, and time is
money, and skilled help is money, and everything else is money, it makes
sense to own a superior machine and to use carbide, because you're not
spending money changing tools, or discarding parts that were made with
dull tools, or sharpening tools, or having a superior production monkey
working the machine who can exercise the right touch to make a superior
job with inferior tools.

But for a one-off in a hobby environment, just sharpen up a HSS or cobalt
drill just for this one time, use plenty of lubricant, and go for it.
You can take ten times as long to do the job and still be happy, and you
should be able to get a satisfactory result.

Then when you're done, sharpen the drill again.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com