A lap charger is a small applicator – typically a wooden block, a hardwood roller, or a proprietary tool – used to press diamond paste, oxide compound, or other loose abrasive into the surface of a metal faceting lap. Unlike sintered or electroplated diamond laps, which carry their abrasive permanently, solid metal laps such as tin, copper, lead-tin alloys, and certain ceramic substrates rely on user-applied charge that must be renewed during use.

How charging works

The cutter places a small quantity of abrasive on the running lap, then presses the charger across the surface as the lap rotates. The wood, with its slightly textured grain, drives micron-sized abrasive particles into the soft metal surface where they are partially embedded. Olive oil or a manufacturer's lubricant carries the abrasive and prevents it from being thrown off by centrifugal force. The result is a thin, even working surface that cuts or polishes at the chosen grit. As the abrasive wears out or is flushed away by coolant, the cutter reapplies. The progression from coarse cutting to fine polish requires a separate charger for each grit to avoid contamination.

Common forms

Hardwood blocks of birch, beech, or hard maple are the traditional charger material. Some faceters use Lucite or Delrin rollers, others use proprietary dressing-and-charging sticks sold by lap manufacturers. The key requirement is that the charger be slightly softer than the lap (so it does not gouge) but firm enough to drive the abrasive in. Storage is grit-segregated and labelled, since one stray particle of 600-grit on a 100000-grit polish charger can ruin an afternoon's work.