Exploded Part Diagram of the Probe
Exploded Part Diagram of the Probe

The term Calibration when it relates to 3D Probe is tad bit overloaded, and can refer to multiple different adjustments:

  • Tool Length Offset (TLO) - This is the button on the machine bed that is used by the machine to understand the differences in length between tools, so that the mapping of Machine Coordinate System to Work Coordinate System can remain consistent despite tool length changes. The TLO measurement operation action is described as calibrate in TOOL drop down menu.

    This is not an adjustment that is made to the probe itself but something done dynamically as part of the machine. Note that on new probes an additional TLO correction is required beyond what can be measured by the TLO sensor itself. As this is the result of the machine TLO sensor and Probe spring rates combined, this cannot be done in advance.

  • The four small set screws (item 14 on the diagram) on the body of the probe. These adjust the concentricity between the shaft (item 1) and the rest of the probe. The probes sold by Serge.Industries have these set screws adjusted so that the stylus tip is within 0.05mm of the exact centre of the shaft.

Instruction card inside the probe box
Instruction card inside the probe box
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  • The effective tip diameter. The tip diameter of the probes sold is 2mm, but this is not the effective tip diameter. Inexpensive probes like the 3D Touch probe do not have a way to compensate for the probe tip tilt and activation distance. Thus probe tip diameter needs to be adjusted to reflect the distance before the probe registers contact. This means the probe tip diameter is not just it’s physical diameter but also adjusted by the activation distance. This value differs from probe to probe due to different spring rates, electronics and tiny stylus differences. The effective tip diameter for each probe sold is determined and the detail included on a card.

Despite the upfront calibration work done before sale, there can arise multiple reasons to re-do the Concentricity and Effective Tip Diameter calibrations:

  • Knocked around during shipment
  • Crashed probe stylus hard
  • Replaced probe stylus
  • Significant temperature swings

The TLO measurement should be done every time the probe is used. If applicable the additional TLO corrections only need to be redone if either the TLO sensor or the spring in the 3D probe are replaced.

Performing the calibrations

Carvera Community Group founder Fae has recorded a video showing multiple alternative ways the Concentricity and Effective Tip Diameter can be performed. This is a short video and watching it to completion, irrespective of the methods chosen is recommended.

The methods that require the least amount of equipment are:

  • Step 1 Method B for Concentricity (centring)
  • Step 2 Method C for Tip Diameter. After having measured the anchor 2 width using a micrometer, or carefully using calipers.