It sounds like both of your machines are loosing steps while carving. As long as the toolpath looks correct when viewed, you should be fine with respect to what is sent to the machine since the preview is based on the actual gcode that will be sent to the machine during the carve.
I would check the following:
- Ensure your feeds & speeds are appropriate for your machine & cutter & material.
- Ensure there are no loose V-Wheels or other components.
- Ensure that there are no loose connections on each stepper motor and connector at the controller.
- If you have a router as a spindle, the lower the speed setting the better for most things.
Those are just some common issues/comments that cause machines to veer off the correct toolpath while carving.
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Brandon R. Parker