Good Day to All! Looking for some help from the resident wizards on how to improve surface finish on circles, arcs and angular cuts. First some background. My vertical mill is a PM-932 converted to CNC about five years ago. The mechanicals are 1600 oz in steppers on X and Y and a 4200 oz in stepper on Z. Ball screws on X and Y are 1605 and the Z is a 2005. All axis have double ball nuts. Gibs are adjusted properly and backlash is no more than .001" inch. I checked cutter runout and it is less than .0008". Spindle bearing preload is set and deflection checked with a DTI. Electronics consist of PMDX-126 breakout board and ESS. Spindle is controlled by a PMDX-107 control board. Control software is Mach3 version 062. I use CamBam and Fusion360 for my gcode generation both with the same surface finish results. X and Y drivers are set to 3200 steps. X and Y velocity is set to 120 and Acceleration is set to 30. Both very conservative settings. Step and Dir pulse is set to 5. Let me know if any further info is needed.

Now onto the surface finish issue at hand. My pictures aren't the greatest but they do show the how bad the surface finish is. The first picture is a screen shot of my stock and part orientation. I'm showing this because machining in X or Y produces a very smooth finish. When combining X and Y for circles, arcs or angular cuts the surface finish is terrible. The second picture is illustrates the smooth surface finish in X and the third picture shows the surface finish on an angular cut. The faceting/scallops are about .030" apart. This cut was made with a 1/4" 4 flute end mill running at 4000 rpm and 20 IPM in 1018 mild steel at .188" DOC. Changing the feedrate and DOC had no effect.

I have played with some of the Mach3 configuration settings and CamBam settings but nothing has changed related to the surface finish. Any insight as to what is causing this and pointers on how to correct it is appreciated.