In article , 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?

Drill press is far easier and better than hand drilling, if you can use
the drill press.

I usually use plumbers black sulfur oil, but it is messy for sure.

What I also use with success is oil emulsion cutting fluid, such as
Rustlick WS-5050, at high concentration (as defined on the label).
This still leaves an oil film, so you will need to clean things if
painting is intended.

Joe Gwinn