As long as you can get the job done with no health risks, then it is correct for what you are doing.
You seem to have the stance and facial expressions correct. Exactly the same as mine.
With regards to power feeding. 90% of my parting off is done under power, the other 10% doesn't need it. I have never trepanned under power, so I can't comment, but I am sure that if you could get up enough courage and try it, it might save you having to wear brown trousers all the time.
Bogs