Printing vases is hard, but I finally managed to get it right:
I kept getting gaps in my vases, which looked for all the world like the motors were skipping during the print. This wasn't simply loosing steps, however, as later layers were still aligned correctly, so something strange was going on. I spent MANY hours over several days trying to see if I could get LinuxCNC to cause one of the goofs while I was watching, to no avail (each print takes almost 4 hours).
Finally, I thought I found a reliable way to cause the glitching by using the Mini gui and enabling the back-plot display. Except it turns out that for some unknown reason, when you enable the back-plot the Mini gui actually pauses real-time motion ON PURPOSE until the plot is generated, then starts things back up again, which was causing the glitch I was seeing. <sigh>
Anyway, since some of the goofs had a bit of the "burned plastic" look about them (brownish discoloration of the normally translucent plastic), I figured I'd try reducing the temperature a bit. Dropping from 180 degrees to 170 helped a LOT, and resulted in only a few errors in a 3+ hour vase print (vs. at least 20-30 usually). Another ten degrees lower, and printing at 160 degrees completely cleared up the glitches, and I got my first clean printed spiral vase (above). Here's a close-up:
I had been happily printing more 'normal' objects (with infill) at 180 degrees without issue both with LinuxCNC and with my earlier Ardunio/RAMPS combination. I never printed a vase with my Ardunio, so I'm not sure yet if the reduced temperature is required because of a difference between the temperature readings on the Arduino/RAMPS board and the BeBoPr with LinuxCNC, or because when printing a vase there's not enough plastic going through the extruder fast enough to keep the hot-end from heat-soaking and causing "mini-jams" or cooking the plastic a bit. Probably a little of both.