A lapping machine turns a flat cast-iron plate while parts held in conditioning rings rub on it with abrasive slurry. It removes only a few microns but makes faces flat to about one light band, which seals without a gasket. Single-sided machines lap one face; double-sided machines lap both faces at once and control thickness closely.
Quick facts
- Main types
- Single-sided, double-sided
- Plate size
- About 300–1,500 mm (11.81–59.06 inch) diameter
- Flatness
- About 1–2 light bands (0.3–0.6 µm)
- Abrasive
- Diamond, silicon carbide or alumina slurry
- Typical parts
- Seal faces, valve plates, gauge blocks, wafers
- Checking
- Optical flat and monochromatic light
Main parts
- Cast-iron or composite lapping plate
- Conditioning rings that hold parts and keep the plate flat
- Slurry feed system
- Pressure plates or weights
- Plate dressing tools
Single or double side?
| Single side | Double side | |
|---|---|---|
| Faces per cycle | One | Both |
| Thickness control | Indirect | Precise |
| Best for | Seal faces, valve parts | Thin parallel parts, wafers, washers |
Good to know
- The plate itself wears and must be kept flat by the rings
- Parts must be cleaned well; slurry left behind causes wear in use
- A polishing stage after lapping gives a mirror finish
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Questions
- How flat can a lapping machine make a part?
- About one light band, roughly 0.3 µm, on small parts, checked with an optical flat.
- Why are conditioning rings used?
- They hold the parts and their own rubbing keeps the plate flat, so the plate does not wear hollow.
- Lapping or surface grinding?
- Grinding removes stock fast; lapping is a final step that gives much finer flatness and finish.
The figures on this page are typical values for guidance, written by Diemeco from standard engineering practice. They are not a specification: confirm grades and properties with the relevant standard or the supplier's mill test certificate, and tolerances with your workshop. Last checked 23 October 2026.