In the pursuit of ever-tighter tolerances, the smallest details make the biggest difference. Probing systems – from extensions and adapters to rotary and swivel joints – are built to keep measurement uncertainty as low as possible. And that uncertainty is often determined by the smallest components in the system, such as the stylus configuration. The key to maximum precision therefore lies in the detail.

Why the Ruby Ball Must Be Polished

Ruby is one of the hardest available materials, surpassed only by diamond. This hardness makes it the ideal contact element: when measuring or scanning, the ball touches the workpiece and transfers the exact point of contact to the machine, which then calculates the part’s dimensions.

For the ball to function as a precise measuring instrument – rather than an abrasive surface that alters the part being measured – it requires an outstanding surface finish. It must be both perfectly spherical and highly polished. Four factors make this surface quality indispensable:

• Minimised friction and wear. A finely polished surface reduces friction as the stylus glides across the workpiece. This prevents the ball from dragging or scratching the surface being measured.
• Reduced material buildup. When scanning soft materials such as aluminium, a rough surface can cause metal to build up on the ruby ball – an effect known as adhesive wear or material transfer. This buildup changes the ball’s effective diameter and causes immediate measurement errors.
• Prevention of measurement errors. A precise «grade 5» surface finish or better – meaning a form deviation of just 0.13 microns from the perfect sphere – ensures that the CMM records the exact point of contact. A rougher surface would introduce inconsistencies into the measurement data.
• Maximum service life. A smooth surface resists the formation of pitting and flat spots that occur when scanning abrasive, hard materials. This extends the stylus’s working life before replacement becomes necessary.

In short: it is the superior surface finish that turns a hard ball into a reliable measuring tool. Where the polish falls short, the measurement error begins.

From Diamond Slurry to Perfect Sphere

This is exactly where our core competence comes in. As a specialist in high-purity polishing slurries and nanodiamonds, we supply the materials that make such surface finishes achievable in the first place. Our polycrystalline diamond powders and ready-to-use diamond suspensions enable the controlled, uniform polishing of extremely hard materials like ruby – down to the sub-micron range and to the spherical perfection that metrology demands.

The fact that diamond is the only material harder than ruby carries a certain elegant logic: it takes the hardest substance to shape the second-hardest. Our experience in processing and stabilising diamond particles is therefore not a footnote, but the foundation for a reproducible, defect-free finish.

This places metrology within a familiar pattern: wherever surfaces determine a component’s function – in optics, semiconductor manufacturing, aerospace or medical technology – our polishing products create the conditions for the highest precision. The ruby ball on a CMM stylus is a particularly vivid example: here, at the smallest scale, the concrete meaning of surface finish becomes visible.