Lapping

Lapping removes microns of material with a slurry and flat plate to achieve extreme flatness, tight thickness control, and ultra-low surface roughness.

Overview

Lapping is a precision abrasive finishing process that uses a charged lap (typically cast iron or composite) and abrasive slurry to remove very small amounts of material. It’s used to produce exceptional flatness/parallelism, tight thickness control, and low Ra finishes on metals, ceramics, carbides, glass, and hardened steels.

Choose lapping when function depends on sealing, bearing contact, or optical/flat reference surfaces—think wafer chucks, valve seats, gauge blocks, and mechanical seal faces. It works best on flat or simple geometries where the lap can contact the full surface.

Tradeoffs: material removal rates are slow, part-to-part consistency depends on fixturing and process control, and sharp edges can round. Deep grooves, heavy warpage, and complex 3D contours are poor fits unless you can isolate the lapped face and protect critical features from slurry contamination.

Common Materials

  • Hardened tool steel
  • Stainless steel 440C
  • Tungsten carbide
  • Aluminum oxide ceramic
  • Optical glass
  • Silicon

Tolerances

±0.0001"

Applications

  • Mechanical seal faces
  • Hydraulic valve plates and spools (lapped faces)
  • Gauge blocks and inspection masters
  • Bearing races and thrust washers
  • Semiconductor wafers and carriers
  • Optical flats and mirrors (lapping stage)

When to Choose Lapping

Choose lapping for flat faces that need controlled thickness, high parallelism, and very low Ra—typically on small to medium parts where removing only microns is acceptable. It fits low to medium volumes when performance depends on surface contact (sealing, sliding, metrology). Plan it as a final or near-final operation after heat treat and stress-relief steps that could move the part.

vs Manual Polishing

Choose lapping when you need measurable flatness/parallelism and repeatable thickness control, not just cosmetic shine. Lapping produces more uniform geometry across the whole face, with less operator-to-operator variation on critical dimensions.

vs Electropolishing

Choose lapping when you must correct geometry (flatness, thickness, parallelism) and remove waviness, not just improve surface chemistry and micro-roughness. Lapping is also the better fit when you need tight contact patterns on sealing or bearing surfaces.

vs Grinding

Choose lapping after grinding when you need the next step in flatness, lower Ra, and tighter parallelism than grinding alone can hold. Lapping also reduces grinding marks and can refine contact patterns without heavy stock removal.

vs Honing

Choose lapping for flat or planar sealing faces and thickness control; honing is primarily for bores and ID geometry. If the critical surface is not a cylinder, lapping is usually the more direct path to controlled contact and finish.

Design Considerations

  • Call out what matters: Ra/Rz, flatness, parallelism, and final thickness with inspection method where needed
  • Leave stock for lapping (often 0.0002–0.002 in per face) and specify the pre-lap condition (ground, heat treated, stress relieved)
  • Protect edges and non-lapped features; add edge breaks where rounding is acceptable and mask features that can trap slurry
  • Limit the lapped area to functional surfaces; large full-face laps increase time and cost
  • Avoid deep grooves, cross-holes, or porous features opening to the lapped face unless slurry containment/cleaning is addressed
  • Define allowable cosmetic appearance (scratch level) separately from Ra to prevent over-processing and cost creep