To accurately measure hits, points are compensated from the center of the probe tip to the part surface. To turn probe compensation on or off, use the Insert | Parameter Change | Probe | Probe Compensation menu item.
There are a couple of things that you should understand when you measure with a portable device.
The XYZ values of the DRO (Digital Readout) are the 3D location of the CENTER of the probe.
When probing a single point on a part, PC-DMIS compensates for the probe radius by doing using one of two methods:
Probe Shaft: Monitoring the angle of the probe shaft and compensating along the vector of the shaft to the point location on the surface.
Pulled Hit: Monitoring the direction of a "pulled hit" and compensating along the direction vector between where the hit button was pressed and subsequently released.
Normally, when measuring with portable CMMs with a hard probe, the probe’s shank vector is used as the hit vector. However, due to the shape of a particular part, you may not be able to position the probe’s shank to get a proper hit vector.
If you want to measure a small, deep hole, but the end of the arm is too large to fit into that hole, you need to take "pulled hits" to get each hit vector to properly point towards the center of the hole, thereby determining the proper in/out compensation. Pulled hits are hits whose vectors match the direction pulled away from the hit location, not the default shank vector of the probe.
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