Seal Face Flatness, Waviness and Roughness: Ra Is Not Enough
A low Ra value describes fine surface texture, not the overall shape of a seal face. It does not establish flatness, and it can leave waviness unaddressed. Treat form, waviness and fine texture as separate requirements, each with its own definition, coverage and evidence. None of the three, alone or together, proves leak performance of the assembled seal. The useful result is a face-specific coverage map that says which requirement each measurement answers.
Three scales on one surface
ASME B46.1-2019 (R2026) is concerned with the geometric irregularities of surfaces. It defines surface texture and its constituents: roughness, waviness and lay. It also defines the parameters used to specify surface texture, and its terms and ratings relate to surfaces produced by processes such as abrading, cutting, wear and erosion, among others. So B46.1 places roughness and waviness together as parts of surface texture, and it treats them as different constituents.
Overall form is a different matter. ASME describes Y14.5-2018 (R2024) as the design language for geometric dimensioning and tolerancing, and its revision places form, orientation and profile in separate sections. A flatness requirement on a sealing face is a geometric control stated on the drawing under that language. It is not a surface-texture parameter, and an Ra value does not report it.
The practical consequence is that one face can be fine in texture yet imperfect in shape. A finish measured over a short trace is silent about variation at longer scales, such as a gentle overall bow or a repeating undulation. The reverse also holds: a face can be flat and still carry a texture that does not meet its requirement.
Keep each requirement with its own evidence
Each of the three needs its own definition, its own coverage and its own operator or method, as the drawing specifies.
| Requirement | What it concerns | What the evidence must show | What it does not answer |
|---|---|---|---|
| Overall form (flatness or other geometric control) | Shape of the face as a whole | The controlled feature, the datum or reference used, and the area covered | Fine texture or waviness |
| Waviness | Longer-scale variation of the surface | The parameter specified, how waviness was separated from roughness and the trace length or area | Overall flatness or fine texture |
| Fine texture (roughness, such as Ra or Rz) | Short-scale irregularities | The parameter, filter and evaluation length stated in the report | Form and waviness |
The table is a recommended review aid, not a form required by either standard. Ra and Rz conversion and report conditions for profile parameters are covered in Ra and Rz on a part's report: read the measurement conditions. This article does not repeat that material.
Map the sealing land
Draw or list the sealing land, then record what was measured where. A single trace across one radius is evidence about that trace. It does not describe the rest of the land.
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Face and land. Identify the sealing face and the width of the land the requirement applies to.
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Form coverage. Record which area the form result covers, and whether the whole land was included.
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Waviness and texture traces. Record where traces were taken, their direction and their length, and whether several positions around the face were sampled.
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Filters and parameters. Keep the stated filter, evaluation length and parameter for each trace, without converting between them.
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Surface condition. Note whether the measured surface is the final surface or an intermediate condition.
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Local damage. Record any scratch, nick or other local defect, and whether the traces would have crossed it. A trace can miss a localized feature.
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Unmeasured zones. Name the parts of the land that no measurement covers.
If a sealing requirement exists, it comes from the drawing, the seal maker or the assembly specification, and no public description reviewed here sets a limit for a track-roller seal. Benchmarks written for other seal types, such as pump seals, should not be carried over to a roller seal.
Separate surface evidence from leak performance
Even when form, waviness and texture all meet their requirements, the result does not show that an assembled roller will keep oil in and dirt out. Assembled sealing depends on the whole sealing system, and it needs its own evidence against its own criterion. Diagnosing a leaking roller is a separate task and is not covered here.
Write the request
State the sealing face and land, then ask for each requirement as its own item: the form result with its datum and area, the waviness result with its parameter and trace coverage, and the roughness result with its parameter and filter. Ask which parts of the land were not measured. Keep any assembly-level sealing claim separate and request evidence for it only if the purchase depends on it.
For a roller from KTSU, provide the drawing, the sealing-face requirements and the report you hold when asking what documentation is available. The public track roller collection identifies the product family. It does not establish a surface-measurement capability or a seal-face finish for any part.
The map is complete when each of the three requirements is assigned its own evidence and coverage, unmeasured zones are named, and any assembled-seal claim is held apart.