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On Thu, 30 Aug 2012 19:59:34 -0500, Tim Wescott
wrote:

I may have asked this before, but I'm slow:

I have some 304 sheet. I use it to make control-line model airplane
handles. Each handle needs to have about 20 1/16" or .050" holes drilled
in it, in a pair of tidy lines.

This stuff breaks my regular old HSS drill bits, and my drill hand-
sharpening mojo is pretty spotty at 1/16".

I'm using them in a drill press. The whole process feels weird -- it
feels like there's a skin on the metal which prevents the drill from
starting to cut unless I feed it fairly hard, but once broken through
doesn't cause much problem. Most of the time that I break a drill bit
it's because I'm feeding it "just a bit harder", then SPING -- I've
broken another bit.

Is there a better drill bit to use, or have I just doomed myself to
trouble? Is there a better flavor of _stainless_ to use? I understand
that 304 is difficult to work with, but it's what McMaster had in the
thickness I wanted; having experienced its joys, however, I'm ready to
consider something else.

I think my next step is to get a dozen 1/16" drill bits, but if there's
some magic material that'll help here, I'm listening.
Greetings Tim,
In your situation I would use stub length cobalt split point drills.
The split point is important. Use a high sulfur cutting oil. Your
local hardware store probably sells some type of cutting oil made for
threading. The dark stuff is usually a high sulfur cutting oil. You
need to make sure there is constant pressure on the drill and that it
is always cutting. If you start the drill gingerly there is a good
chance that the 304 will work harden and then the pressure it takes to
get the drill to cut goes way up. So start drilling like you mean it.
Also, back up the sheet with another piece of metal. Aluminum is fine,
mild steel too. Even hard maple might be OK. You don't want the sheet
flexing away from the drill. This lowers the cutting pressure which
leads to work hardening. Drilling into mild steel might be the best
because it is close to 304 in hardness(but not nearly as tough!) and
this will help prevent a burr being pushed out of the 304 and into the
back up material. So you end up with cleaner holes and the dril is not
as likely to break as it exits the 304. Ideally the drill should be
spinning at about 2400 rpm. But this means you would need to feed the
drill fast through the part to make sure it is cutting the whole time.
Less than a second to go through 1/16 material. So maybe slower speed
with constant pressure right from the start will be best for your
situation with the drill press.
Eric


Suggest maybe a carbide spade drill--although he''ll get a tubular exit
burr, the sheet won't lift up due to flute helix causing slippage etc as it
breaks through.

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