Gunner Asch fired this volley in
:

Anyone had any luck sharpening their own files with acid? What
type,
how long, etc etc.

Gunner, I've tried it, with several variant "resist" methods. Muratic
acid likes iron.

The results go from "not at all" to "Gosh! That worked!" to "DAMN! It
took ALL the teeth off!".

The only resist method that I've found that ever worked for me was to
firmly draw the file backwards over a hard, rounded-profile with a
single thickness of bed-sheet cotton damp (but not WET) with oil.

This is NOT a trick that works very well for that emergency shipment
of files to a new machinist. You might frustrate hell out of her.

The one thing I have found about this method, and why I stopped doing
it, is that the new edge you get has no backup metal, and dulls very
(very!) fast.

LLoyd