Spindle misbehaving

[savannahdan]

I've worked on a couple of projects this week during which the spindle will travel at various speeds (some regular speed and others extremely slow) along the outline of the projects and then makes a side cut in the project material.  The spindle appears to maintain speed and the issue has only involved travel along the x and y paths.  I keep the system lubricated and clean it before each job.  The cuts were with a 1/4" end mill and they were fresh.  Anyone have any ideas what is going on?  Thank you.

BTW, I was able to salvage both jobs with some sanding and modifications.

[savannahdan]

One of the differences I made on these files was to add a ramp cut. I decided to experiement by eliminating that and rerun the files. I'm not getting the same slow down and run off.