On Friday, July 10, 2015 at 3:24:58 PM UTC-5, 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 bought about 8 gallons of Chevron water soluble oil at an estate sale a few months ago ($8). Haven't touched it because I didn't know for sure if it was usable in my all-manual shop.
I mostly cut mild steel and aluminum, using WD40 on aluminum. I did take a small job in SS which gave me fits. Would the soluble oil have made that cut better?