A Cratex wheel is a rubber-bonded abrasive tool manufactured by the Cratex Manufacturing Company, widely used in jewellery finishing, metalsmithing, and lapidary work. The wheels consist of silicon carbide or aluminium oxide abrasive particles suspended in a vulcanised rubber matrix, a construction that distinguishes them from rigid grinding wheels and gives them a characteristic resilience. That flexibility allows the working surface to conform slightly to curved or irregular forms — a property of particular value when cleaning castings, refining filigree, or pre-polishing cabochon girdles and metal settings.

Construction and Available Forms

Cratex wheels are produced in a range of grits, from coarse through medium to fine and extra-fine, and in several degrees of rubber hardness. The combination of grit and bond hardness determines the aggressiveness of the cut and the surface quality left behind. Coarser, harder wheels remove material quickly and are suited to deburring and smoothing rough castings; finer, softer wheels leave a pre-polish that requires minimal subsequent work. The product line includes full-sized bench wheels, smaller mounted points, and tapered or cylindrical shapes intended for flexible-shaft handpieces such as the Foredom, making the system adaptable to both large-scale finishing on a bench motor and detailed work under magnification.

Working Characteristics

The rubber matrix serves two functions simultaneously: it acts as the binder holding abrasive particles in place, and it provides a degree of give that rigid wheels cannot offer. When the wheel contacts a convex or recessed surface, the rubber deforms fractionally, increasing the effective contact area and producing a more even abrasion pattern. This behaviour reduces the risk of creating flat spots or witness lines on curved metalwork — a common problem with hard wheels on soft precious metals. The wheels wear slowly relative to their cutting rate, and because fresh abrasive is continuously exposed as the surface wears, cutting efficiency remains relatively consistent through the life of the wheel. They are used dry or with minimal lubrication; coolant is generally not required at the speeds typical of bench-motor finishing work.

Applications in Jewellery and Lapidary Work

In the jewellery workshop, Cratex wheels are most commonly employed at the stage between filing or grinding and final polishing. Typical tasks include:

• Removing investment residue and surface porosity from lost-wax castings
• Smoothing solder seams and file marks on gold, silver, and platinum
• Refining the girdle and base of cabochon stones before the final polishing lap
• Cleaning up prong tips and bezel edges without distorting the metal
• Deburring drilled holes in shell, bone, and softer lapidary materials

Because silicon carbide is harder than most gemstones on the Mohs scale with the exception of corundum and diamond, fine-grit Cratex wheels can also be used directly on certain stone surfaces for shaping and pre-polishing, though dedicated lapidary wheels remain the standard for serious stone work.

In the Trade

Cratex wheels have been a standard consumable in North American and European jewellery workshops for several decades and are stocked by most jewellery supply houses. Their longevity and consistent performance have made them a default recommendation in bench-skills instruction, and they appear routinely in curricula at jewellery schools and gemmological programmes that include a practical fabrication component. The brand name has, to a degree, become genericised in workshop parlance, much as certain other proprietary tool names have come to denote a category rather than a single manufacturer's product.