Gunner Asch wrote:
On Mon, 13 Jul 2015 16:03:19 +0000 (UTC), Cydrome Leader
wrote:

wrote:
On Fri, 10 Jul 2015 20:24:56 +0000 (UTC), Cydrome Leader
wrote:

I need to drill about 100 holes (around 5/16") in 1/8" hot roll plate. I
usually just use cutting oil from the hardware store, works fine, makes a
huge mess. Steel tube will be welded to the plates, each drilled with with
4 holes for fastening to supports for countertops.

Welding instructor uses a spray bottle of a water based coolant, something
milky looking. It's not as messy and doesn't make everything rust either.
I tried it, but with a dull bit, it wasn't really a test of anything
meaningful for the short time I tried it out.

Any real difference between the two for hand drilling or use with a drill
press, or good reasons to pick one over the other for specific jobs?
I make my living as a machinist using CNC and manual machines.
Virtually all the machining I do uses water soluble oil at about 8%
concentration in water. It works great. A big enemy of HSS drills is
overheating. The drill steel gets relatively soft and dulls. When hand
drilling this can be a problem because it is often hard to apply
enough pressure to keep the drill bit cutting and the operator often
has the drill spinning too fast. So a water soluble oil coolant works
well because not only does it supply high pressure additives it also
removes heat very fast and keeps the drill bit cool.
Eric

Any favorite coolants you use? I'll order something something from MSC.
Prices range from $35 to $50 for a gallon for the water based coolant
concentrates.

For drilling with plain cutting oil, I tend to be happy when the oil just
starts to smoke, and for whatever reason, I've always had better luck
with HSS bits over cobalt which I tend to ruin faster. The HSS can be
cleaned up with even a worn out stone and will cut again.

Any suggestions for how hard you can push things with the water based
stuff? A few squirts from the spray bottle here and there is the amount
I'd be able to apply.

Well..many of my clients run cobalt or tungstun at 2000-3000 and
.003-.009 per rev feed. HSS tends to go down to 800-1200 at the same
feed rates

This of course depends on the size of the drill bit. Remember...the
bigger the bit..the slower you turn. Feed rates remain the same.

I suspect it has something to do with the angles they bits are cut. The
cobalt stuff from a good hardware store is usually 135 degrees. I seem to
wear the tips out real quick, large or small. Never really figured out
why.