Thanks for that tool! Seems like it is very useful.
Found this comment on a youtubevideo which also used a drill. Makes sense, learnful lesson for the next time:
ER You should NEVER rotary lap a valve in esp with a drill, it HAS to be a BACK AND FORTH action then LIFT OFF the seat to reset the valve paste on the seat, (as the paste grinding sound goes quieter usually 4 or 5 times ) then turn the valve a few degrees and then rept motion. like starting a fire but if you rotate it, you burn scars into the seat,, meaning the valve seat gets hotter and clogs with carbon deposits in these scars, which then burns the seat again meaning another head rebuild. And you start the VALVE Grinding with COARSE paste, then clean off and move to a SMOOTH grinding paste for a nice consistent groove free flat greyish looking seat ! The best way to check if it has worked is to use a soft pencil like a HB and scribe three vertical lines at 120 degrees apart on the seat when you refit the valve on the seat twist the valve when in contact with the seat and the 3 pencil marks will rub evenly along the seat, if not then the seats need regrinding again or you need new valves and or valve guides.,