From what you said:
-RPM of the spindle may not be right. What kind of inverter do you have? Does the inverter have a display that shows the Hz or RPM? When you run at 500RPM the display of the inverter should show 1000RPM. Or get a tach to check the RPM of the spindle.
-Clock speed of the axis travel may not be right. Check the clock speed and set for what is recommended in the manual.
-The gain in the SETP may not be right.
Hope I was of some help.
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