Basics of Coordinate Metrology
Unit 7: Structure of Coordinate Measuring Machines - Stylus

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In order to meet the wide range of measurement tasks with their different requirements, there are styli containing different stylus tips in different dimensions and designs. The individual styli can be combined to give complex stylus systems suited to specific measurement tasks.

  • Conical-tip styli are used to localize the position of bore holes. They self-center during probing. Conical-tip styli can only be used to determine 2-dimensional coordinates.
  • Spherical-tip styli are the standard styli for coordinate measuring machines and have the widest range of application. A stylus sphere usually consists of synthetic ruby. These sphere are manufactured with extremely small form deviations, are insensitive to corrosion and almost free of wear. The stylus sphere diameter is usually between 2 and 10 mm.
  • Universal styli are spherical-tip styli which additionally have a joint that allows the direction of the stylus to be adjusted as required by the specific measuring task. The stylus has to be requalified after each adjustment. Qualified positions can be restored with a repeating precision of 1.5 µm by means of precision universal styli.

  • Stylus tips are used to measure very small parts or the microstructure of surfaces and the like. Stylus tips are also suitable whenever a stylus sphere radius correction transversally to the stylus tip is not possible or desired.

  • Cylindrical styli are used to measure thin metal sheets. They allow safe lateral probing of flat parts. As in the case of conical styli, they can only be used for 2-dimensional measurements.

  • Disk-shaped styli are used predominantly for measuring features where access is difficult (hollows, etc.). . Probing is done with the lateral surface of the stylus disk, which on the one hand only allows a 2-dimensional determination of coordinates and on the other results in strong filtering of the surface roughness as a result of the usually large disk diameter.

  • Star styli are star-shaped combined spherical-tip styli that allow the part to be probed in any desired direction. While the probing of lateral surfaces by means of spherical styli is possible only to a limited degree, star styli have the option of selecting the stylus tip that is orthogonal to the probed surface. Each stylus tip of the star stylus must be qualified separately.