I got it pretty close on the lathe but to get the final fit I used 180 sandpaper so the ferrule just barely fit.
Drilled the first hole to match the small end of the file then drilled part way with a bit that was a little smaller than the wide end.
Held the file in one hand and beat on the other with my carving mallet. This was a small flat metal file. 1/2" wide and 10" or so
Sprayed it with a few coats of lacquer and all's well
I stood out in the sun and sprayed all 3 coats quickly rotating the handle for quick drying and no running.