On Fri, 10 Jul 2015 15:10:20 -0700, 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

Ayup! Good post