leeburk@a... wrote:
> but haven't I heard in the ancient past that sometimes something softer can be
used to cut something harder?

Ooh - that's a nasty and deceptive partial truth/understanding there.

What you're semi-recalling is that *when lapping* the harder of the two metals
(commonly cast iron and high carbon steel, in engineering circles) is worn away.

But the thing doing the wearing is diamond or SiC grit, which is harder
than both.

The explanation is that the abrasive particles embed in the softer
material, and (hence) scrape over the harder material.

In model/workshop engineering some processes use
lead laps to work mild steel.

  BugBear