PH20 stylus selection

NOTE: Choosing the best stylus for a given application is an important factor in achieving optimum probe performance. For further information on the full range of Renishaw styli, please refer to Renishaw's styli and accessories brochure (H-1000-3200) which can be ordered from your supplier or downloaded from Renishaw's web site, www.renishaw.com.

When selecting a stylus, it is important that the stylus length is kept to the minimum required to access all features to be measured, and that the stylus type offers the maximum possible stiffness. Factors that affect stiffness are:

  • Joints in the styli: these tend to reduce rigidity and should therefore be kept to the absolute minimum
  • Stem diameters: that are governed by the ball tip diameter of the stylus
  • Stem material: that can be stainless steel, ceramic or graphite fibre

It is also important to ensure that the stylus ball diameter chosen is as large as is practical. This not only ensures that the stylus will be as stiff as possible, but also reduces the stylus's susceptibility to surface form and surface finish.

Owing to the modular construction of the TP20, when selecting and using styli the following criteria should be applied:

  • Work only within the recommended stylus limits for each probe module (refer to 'Recommended stylus limits' below)
  • Always use the shortest possible stylus
  • If using larger styli than those recommended for use with each probe module, always conduct trials to establish the effect on measuring performance
  • Minimise the mass of styli by using either ceramic or graphite fibre stems

Recommended stylus limits

Owing to the modular construction of the TP20 probe, it is recommended that the limits shown in the following figures are applied when selecting styli to be used.

The low force probe module

The low force probe module has the following recommended stylus limits:

  • Steel and carbide styli up to 30 mm long
  • No star or cranked styli

Recommended stylus limits for low force probe module

The standard force probe modules (SF, EM1 and EM2)

The standard force probe modules (SF, EM1 STD and EM2 STD) can be used with the following range of styli:

  • Steel and carbide styli up to 40 mm long
  • Renishaw graphite fibre (GF) type styli up to 50 mm long
  • Star and cranked styli up to 20 mm offset

Recommended stylus limits for standard force probe module

The medium force probe modules

The medium force probe modules have the following recommended stylus limits:

  • Any stylus type up to 60 mm long
  • Star and cranked styli up to 20 mm offset

Recommended stylus limits for medium and extended force probe modules

The 6-way probe module

The recommended stylus limits for the 6-way probe module are:

  • Any stylus type up to 30 mm long
  • Star and cranked styli up to 10 mm offset

Recommended stylus limits for 6-way probe module

Comparative stylus lengths

A comparison of the minimum and maximum stylus lengths for use with each probe module is shown below:

Comparative stylus lengths for TP20 modules