Larry Jaques wrote:
[re - grinding head off nails]

Were you using a small, sintered carbide ball?

No, but that's a good idea. I was using a cylindrical carbide burr. I
don't have a carbide ball, but I do have an HSS one that I can use for a
trial.

(and 3 layers of eye protection?)

Indeed - those burrs send out millions of TINY, needle-like, slivers!

Thanks,
Bob