You can often improve a keyless chuck that releases too
easily. Disassemble and degrease the parts. Check for
burnishing on the conical surface inside the hood where the
jaws ride. Scuff up that surface with crocus if you can see
shiny tracks from the jaws. Relube the parts before
reassembling, but do not get any grease on the inside of
the hood or the mating surface of the jaws.

Ned Simmons

Ned,
Translation for us Brits please.
What is crocus?

John