Bell skiver - what causes these lines and inconsistencies

That's pretty much it. Enough to keep the edge sharp but not as much pressure on the stone for a reprofiling. I do it more by ear because it's pretty tough to see out the left side of the machine while you're feeding.

Another thing I've done (that I saw on a video somewhere) was to use the bell to re-profile my rubber feed wheel so it perfectly matched the curvature of the knife. This also takes the top oxidized layer off the wheel and seems to make it a bit stickier.

The best way I've found to do this is by moving the bell knife blade towards the feed wheel rather than raising the feed wheel into the blade.....

While we're on belknife tips and tricks I like to do a double bevel on my bell blade. Not sure if this is the correct terminology but I basically start by grinding the knife high and towards the shaft then a narrower grind to the edge. Similar to the edge on a Chartermade skiving knife.

I'm typing this on my phone with a broken screen so if any of it isn't clear I'm happy to clarify. Hopefully these tips work for you.