I’ve found when trying to perform part pick ups in a sinker one can get unreliable results if your not aware of some of these tips and tricks.
• Make sure your part is clean and free of oil or debris, this even includes dust particles if possible.
• The best surface to probe is going to be a ground surface, anything surface ground with a 60grit or finer wheel.
• Machined and EDM surfaces can have peaks and valleys so you may notice a small variation when slightly moving your probe location between pickup routines on the same surfaces. This typically isn’t a game changer but is something to be aware of when trying to hold very small part tolerances.
• Make sure your probe is clean and calibrated if not on true center of your spindle.
• I’ve found some machine manufactures use a higher probing voltage, through time this will erode the tangent points on the sphere leaving very small flat spots on your probe. This of course can only be seen under magnification or when using a micrometer to verify probe diameter. An easy solution would be to index your C axis at a different rotation once you know this to be happening, or of course replace the consumable part of the probe.
• Most modern machines have a function to set probing tolerance, so you could set the tolerance at .00005 and set the number of times to check the part. Then if the machine does not repeat inside that tolerance it will alarm you. This can also be done manually by probing the part twice and comparing results.
• Lastly regardless of your machines age or accuracy capabilities I’ve found that if time permits, leaving the Edm fluid raised to just below part probing height is very affective. What this will help do is stabilize the machine casting and the part to the same temperature. This will help minimize the effects of thermal growth caused by the difference in ambient air temperatures.