I'm not sure if this is the right place to be posting this, (I'm new here) so if it's not any suggestion on a better location would be appreciated.

I recently purchased a used machine (Digital Tools RD-903-1) and for the most part it works well but it does give me some accuracy issues. It's have a 5' x 10' cutting area with stepper motor and a Porter Cable router, I'm using Vcarve Pro for the drawing and a older version of Mach3.

What happens is if i cut a small circle say round 1.5" diameter, it isn't perfectly round, but if i cut that same circle over and over again it is constant. If I cut a larger circle say around 8" diameter it fine. I did a test, where I put a 4' x 8' sheet on the table and cut out 11" x 11" squares and there weren't all the same. It was only a small difference but it seems that the accuracy is different at different placed on the table.

Does anyone have any ideas on what I can do or what the issue is.

Thanks,