Choosing styli for scanning
Choose the right stylus for your application
The choice of scanning styli will be dependent on the scanning application and the type of scanning probe used. Use a stylus which has the same diameter as the finished cutting tool used to produce the part.
Keep the stylus as short as possible to prevent excessive bending, but ensure the stylus is long enough to prevent scanning on the shank.
With point measurements, the ball only comes into contact with the component's surface for a very short time. Scanning is different as the ball slides along the surface of the work piece. Because the contact is continuous, there is a prolonged sliding contact between the ball stylus and the surface of the workpiece.
Renishaw has run an extensive research programme to examine the interaction between ball materials and work piece surfaces. All the tests with ball materials have shown that materials are deposited on ball surfaces. Between inspections, it is recommended that the balls are cleaned with a dry, lint free cloth so that no residue is left.
Abrasive wear (scanning abrasive materials)
If, for example, components made from cast iron are being measured, both the ball stylus and the surface of the work piece can suffer wear from abrasion. Minute particles of residue can cause fine scratches on the ball stylus and the surface of the work piece. We recommend zirconia ball styli for this type of application to minimise this effect.
Adhesive wear (scanning aluminium parts)
When a ruby ball is used to scan an aluminium surface, the two materials attract one another. The material is usually passed from the softer surface to the harder surface. This means that aluminium is deposited on the surface of the ball and the coating of aluminium can be seen clearly after only 100 m of continuous measurement using a single contact patch on the stylus ball. We recommend ball styli made from silicon nitride for this type of application. This material repels aluminium, so the deposit effect rarely occurs.