A lap dresser is a tool used to true the surface of a worn or contaminated faceting lap, restoring flatness and removing high spots, glazed regions, or contamination from a previous grit. Dressing brings a lap back into service without resorting to the more drastic remedy of resurfacing on a lathe.

Forms and use

The simplest dressers are silicon-carbide or aluminium-oxide stick assemblies, mounted in a holder that allows the cutter to hold the abrasive flat against the lap as it rotates. More elaborate dressers use a diamond-impregnated nib or a tungsten-carbide cutter, drawn slowly across the lap to remove a controlled amount of metal. For solid-metal laps such as tin, copper, and lead-tin alloys, a wooden block charged with coarse abrasive will restore the working surface and then accept a finer charge for the cut grade required. For sintered or plated diamond laps, a dressing stick that exposes fresh diamond by removing the loaded swarf is the preferred tool; aggressive metal-removal dressing destroys the bonding matrix and shortens lap life.

When to dress

A faceter knows a lap needs dressing when cuts that previously ran cleanly begin to drag, when polish quality drops without other change, or when the working surface visibly glazes. A dial indicator on the lap face will quantify out-of-flat conditions exceeding the cutter's tolerance. Dressing is part of routine machine maintenance and most working cutters dress polish laps lightly between major projects rather than waiting for performance to degrade.