Garry,
This might seem to be a simple question, but this type of mill has caused problems getting a good surface finish for others as well.
Have you tightened up the quill lock before cutting?
I ask this because the RF type mill/drills (of which yours is a clone) have a tendency for the quill to go up and down at will if not tightened up, so the cutter can go up and down as it travels along the job. On the one I had, there was about 20 thou up and down movement of the quill. Grab hold of the quill, with the lock off, and see if you can lift it up and down.
All sorts of fixes have been tried over the years, and I eventually fitted a long compression spring onto the depth stop to keep the quill in the upwards position, but I would always still use the lock as well, others have used pulleys with weights hanging on the end of wires, long tension springs etc to get that quill up.
John
Edited By Bogstandard on 11/09/2011 18:45:00