"J. Clarke" wrote

7/8 Forstner, in drill press at lowest speed (350 RPM). Carbon steel. Bit
sharp (how do I know? Worked it over with a fine grit diamond file las
time I used it. This time I managed to slice myself taking it out of the
box--it didn't hurt until I saw the blood).

Could be you got it too hot before you sharpened it, and it lost its temper.

Though I would remind you that the larger the bit, the slower the speed is
required. 250 RPM might be slow enough to do the job.
--
Jim in NC