CMM touch probes measuring a machined part

Spindle Probes and Tool Setters

Probing turns a machining center into a measuring tool. There are two kinds of probe, and most production machines benefit from both.

Spindle probes

A spindle probe sits in a tool holder and is loaded like any other tool. When its stylus touches the part, the probe signals the control by radio or infrared, and the control records the axis positions.

  • Setup: find edges, bores and surfaces and set work offsets automatically instead of with an edge finder.
  • Alignment: measure how a part sits on the table and rotate the coordinates to match.
  • In-process checks: measure a feature after roughing and adjust the finishing pass.
  • First-part checks: confirm key features before the part leaves the machine.

Good probes repeat to around a micron. The machine's own accuracy and temperature still limit the measurement, so probing doesn't replace a CMM for final inspection.

Tool setters

A tool setter is mounted on the table. Contact setters measure tool length, and on some models diameter, by touching the tool to a sensor. Laser setters measure the tool spinning at speed without contact, which captures runout and works for very small tools.

  • Tool offsets: length and diameter measured automatically instead of with a height gauge.
  • Broken tool detection: check a drill or tap after the cycle, before the next part.
  • Wear tracking: remeasure tools and update offsets as they wear.

Payback

The gains are time and scrap. Setup that takes minutes by hand takes seconds with a probe, and a broken tap caught after one part is cheaper than a pallet of parts without threads. On unattended runs, broken tool detection is hard to do without.

Keep them accurate

  • Calibrate the spindle probe on a ring gauge or reference sphere regularly, and after any crash.
  • Keep styli tight and undamaged, and replace bent ones.
  • Keep laser setters clean. Coolant mist and chips cause false readings.
  • Run probing cycles at the feeds they were calibrated at.

Measurement is part of how we check machined parts; see CNC machining.

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