Yeah after literally buffing well over a thousand pieces
you do tend to get a feel for the light pressure needed, essentially you're 'sanding' with mild abrasives instead of a disk or belt as you would with a sander. I remember reading somewhere that 'tripoli' was comparable to 1200 grit, don't quote me on that, but I tend to agree
You mentioned sanding, and I gotta tell you that's a loaded question, almost all pieces of my puzzles receive a very 'used' 120grit belt sanding before lacquer but my boxes get a more extensive sanding regime, mostly because of my 'slipfeather' technique which requires starting sanding with as low as 60 grit moving all the way up to 600 so...60-80-100-120-150-180-220-320-600
As a side note, some of the woods that I've found take really well to this extensive sanding 'ritual' are Bloodwood and Jacaranda Pardo, they almost have a glass like finish even before lacquer and buffing! Now in addition when I make pens, I generally start sanding at 320 and work up from there using MicroMesh sanding all the way to 12,000 grit
followed by a boiled linseed oil and CA glue finish, then usually skipping the tripoli and straight to the white diamond finishing up with 'Renaissance wax' and final buffing
I will try and do a video capture on my camera showing a puzzle piece being buffed, to hopefully show things more clearly, I'll post it here when I get it done.
Here's the link to my you tube video showing the buffing process, hopefully this will help http://www.youtube.com/watch?v=jGMQR8kNV_w