John, You are correct on white lines of material. I haven't had that in years, but I don't do many pens. What I learned early on with white lines was a combination of two things for me - 1. CA not yet cured (hard but not cured) and 2. too much speed and/or too much pressure.
The results for me was that CA, when not fully cured, and too much pressure or speed - was that the sanding dust from the CA under the MM would heat up, melt the dust which would form into little balls and then cure the from the heat and scratch the devil out of the CA finish.
CA, when thicker layers are wanted, takes longer to cure. IF applied with Paper Towel, most of that does cure well enough that MM will not affect it that much. But for me, the thicker layers (which I like) take longer to cure. And that is not a problem for me as I spend as much time as I need for each pen. I'm not in a hurry. But if I do rush too much and sand before fully cured, and add a little too much pressure on the MM, that builds up more heat on the MM which in turn creates sanding dust into little bits/balls of heated acrylic which cause trouble or white scratches.
I learned this back when MM was cheaper, and the experience that came from that use has stayed with me. Sometimes I take that for granted. MM is not fool proof and requires its own technique.
THAT brings me to another related subject - it sure is nice for some of you guys to pass on what you learn because - to some of us old timers take some of the processes for granted when they become second nature to us, and we think that "everyone" knows this. Jon Rista (jrista) is one who questions us old-timers quite often. While I do banter with him, it is good for him and others who pick up on things that some of us take for granted, and explain to the newer generation of young and old pen turners!
