I bought a 3-hole sink and now want a 4-hole. What is the tool of choice for cutting a hole in 18 gauge SS? For a home shop, is some sort of hole saw appropriate? Thanks for any suggestions.
I would use one of those cone shaped step drills for the cleanest hole. SS is nasty stuff. A hole saw will probably work, but is likely to leave a ragged hole.
Go to a rental shop and ask for a chassis punch.
There are manual and hydraulic units.
Most rental places have the hydraulic units and a decent set of punches.
What you want to do this job NEATLY is a carbide tipped cutter. see...http://www.milwaukeeconnect.com/webapp/wcs/stores/servlet/category_27_40028_-1_192330_192327
You need a Greenlee hole punch.
Here is a link that might be useful: Hole punch