Some days ago I got a nice little USB Microscope [1]. Now I can precisely zero the X and Y axis. My setup was as follows:
#1 Engrave a small point. #2 Jog the spindle until you get the crosshair [2] centered to the mark. #3 Enter the offset values to Settings/Camera (activate OMR first). #4 Now you’ll get a blue button called “Set Offset”. #5 Push it and get happy.
I have the same microscope but it tends to drift in x/y a bit when adjusting focus. I planed on using it for accurate pcb jobs with <0.1mm of precision needed. You must take all readings at a known height and focus point. Having it perfectly perpendicular to the surface and parallel to the z axis is another requirement, you can acheve that by placing a large flat mirror on the bed, the image of the scope’s lens should be dead centered.
