Bob Engelhardt fired this volley in
:

I see the drill motor & PWM drive as the weak link, especially
regarding constancy of feed. For a powered feed on my lathe, I used a
servo amp with tach feedback and it's amazingly constant:
http://www.mwdropbox.com/dropbox/ServoPowerFeed.pdf
Buying the servo amp might be less satisfying than building your own
PWM drive, but I still get a REAL NICE feeling every time I use my
power feed.

That was my whole point. It's not just "not quite the best solution", it's
a cobbled-up thing bound to disappoint fairly soon after implementation.

Lloyd