Wing rear spar countersinking

The thin aluminum on the top the rear spar seems almost to thin to countersink. Aside from using the micro stop countersink, is there a better way? I tried a test run with a deburring tool and it seemed to do a respectable job. ( note: some of the notes are from previous additions so they may not be applicable)

I used the doubler flanges as support for the countersink pilot. See here for more information about how I got the job done ... https://vansrv14project.uk/2018/08/14/15-04-rear-spar-machine-countersinking-dimpling/