Lapping FAQ: the questions buyers ask

Lapping is a fine finishing process where the part is rubbed against a lap with a loose abrasive slurry. It is used for achieving extreme flatness and a very fine finish on sealing and gauging faces. This entry explains what it is, what the numbers on a data sheet mean, and what to put on a drawing.

It is written from the point of view of the buyer and the drawing office: the values that are realistic in production, the ones that cost money, and the way the result is verified. Where an industry sets the requirement, automotive is used as the example: a fixed takt, because a late delivery stops the line.

The questions buyers ask

What is Lapping used for?

It is used for achieving extreme flatness and a very fine finish on sealing and gauging faces. A fine finishing process where the part is rubbed against a lap with a loose abrasive slurry.

What tolerance can be held?

±0.002 mm with flatness to 0.001 mm is typical, held on the features that carry the function and confirmed by optical flat with a monochromatic light source.

Which material should be specified?

316L stainless steel is the usual choice; the certificate requirement is in-house approval with dimensional reports.

What finish comes as standard?

Ra 0.05 µm achievable. A finer finish is a separate operation and is quoted as one.

How long does it take?

A realistic cycle is 30 to 120 minutes for a set of faces, and the cost driver is skill and inspection time, because it cannot be hurried.

What information is needed for a quotation?

A STEP or IGES model and a PDF drawing with tolerances, material and finish called out, plus the quantity and the expected repeat frequency.

Can the same result be guaranteed on a repeat order?

Yes, because the fixtures, tool lists and verified programmes are retained for the life of the part number.

What is the most common mistake on the drawing?

A lap that has lost its flatness, which transfers an error onto every part.

Applications

Lapping is used for achieving extreme flatness and a very fine finish on sealing and gauging faces, and in practice it appears most often in seal faces, gauge blocks, valve plates, optical mounts.

How it fits into a machining route

The route is fixed before the first part is cut, and it is the route rather than the individual setting that holds the result: skill and inspection time, because it cannot be hurried. Where a drawing calls for something the route cannot hold economically, that is raised at quotation rather than after the parts are made.

Standards, documentation and what is issued

The documentation requirement is in-house approval with dimensional reports. Material is supplied against a certificate where the application calls for it, inspection results are recorded with the job, and the records are kept so that a repeat order can be compared with the first instead of being measured from scratch.

Optical flat with a monochromatic light source is the verification step. Where a customer format or a standard report is required, it is agreed before the batch starts, because a report written after the event is a report nobody can use.

Frequently asked questions

What tolerance should be specified for Lapping?

±0.002 mm with flatness to 0.001 mm is realistic in production. Tightening it beyond the functional requirement increases cost without improving the part.

Which material is usually used?

316L stainless steel is the usual choice, supplied against in-house approval with dimensional reports.

How is the result verified?

Optical flat with a monochromatic light source, with the results recorded so a repeat order can be compared with the first.

What is the most common mistake?

Embedded abrasive left in a soft material, which later scores the mating face.

How long does it take and what does it cost?

A realistic cycle is 30 to 120 minutes for a set of faces, and the cost driver is skill and inspection time, because it cannot be hurried.

Related capability

If you are specifying Lapping on a drawing and want a second opinion on the route, send the model and the quantity. The first response is a manufacturability review with the likely risk points and a quotation, so the decision can be made on facts rather than on a price alone.

Machining, inspection and documentation are handled in one place, which is why the dimensional report and the material certificate arrive with the parts rather than after them.

Related entries

These entries sit next to Lapping in the encyclopedia: High Speed Machining, Thread Milling, 7075-T6 Aluminium. Reading them together gives a fuller picture of how the process, the material and the measurement affect each other.