Flat Lap Machines: A Buyer's Guide

What a flat lap is for

A flat lap machine turns a horizontal disc (the lap) while you hold the work against it. It is the standard way to grind and polish a flat surface: slab faces, the backs of cabochons, specimen faces, bookends and tops of geodes. The same idea sits at the heart of a faceting machine, where a precisely controlled stone is presented to a flat lap.

Rotary and vibratory laps

• Rotary laps spin one disc. Changing the disc changes the grit, so you can work from coarse to polish on one machine.
• Vibratory laps shake a flat pan rather than spinning it. They are gentler and quieter, and well suited to polishing flat pieces and lapping many pieces at once.

What to check

• Flatness and run-out: a lap that wobbles cannot produce a flat surface. Spin it and watch the edge.
• Disc fit: make sure the discs, plates or pads in the sizes you want are still easy to get for that model.
• Splash control: a good splash guard and drain make the difference between a clean bench and a wet one.
• Speed control: useful when you move from grinding to polishing.

Working with water

Run water over the lap while you work. It keeps the stone cool, carries away debris and extends the life of the disc. Never run a diamond lap dry.