I'd think you could sharpen the chasers by grinding across the top using the side face of a fine bench grinder wheel – carefully. Probably hold the chaser with a mole wrench or parallel clamps.

To do the job properly you really need the proper jig in which to hold the dies for sharpening.

If you get the hand grinding wrong, you may well end up worse off than if you left well alone.

My advice FWIW is find someone with the kit to do the job correctly.

Howard

I have a pdf of The Book of the Coventry Diehead (25th Ed). It mentions UNC and UNF, so is post-1949, perhaps late-50s to 1960s. I don't know where I downloaded it, so can't post a link.

It mentions several jig types, including one for 12 degrees rake angle. It also mentions M-type dies are ground parallel to their back. I enclose a couple of pics from the book for a type which allows different rake angles.

It shows the clamps on the left for grinding top rake, and on the right for grinding the 'throat' or lead-in of the die.

My recollection from long ago (unreliable) is that the die rake angle was zero degrees, and that there was a simple jig, perhaps shop-made, not a branded one, for use on a cutter grinder or surface grinder.

Larger copies are my album.

Bill

Try John Dunn Engineering. Advertises in ME magazine.

I believe he has the jigs.

Best regards,

Steve.