C Lay circular
Lay circular · Estado superficial · ISO 1101 + ASME Y14.5
Example in plan
How to interpret it
On the drawing, “Ra 1.6 C on turned face” states a lay circular requirement.
What controls
Lay symbol requiring the marks to follow concentric circular paths about the center of the indicated surface. It is the natural pattern of a face turned on a lathe or of a surface generated by a tool rotating about the center of the part. On bearing and sealing faces, circular marks form continuous rings, which has a very different effect on sealing than radial marks.
How to verify
Visual check under grazing light that the marks describe concentric circles about the indicated center. Roughness is measured with the stylus traversing radially, which is perpendicular to the lay in this pattern; measuring along a ring would give a meaningless value. Measure at several radii, because in facing the finish changes with diameter if cutting speed is not held constant.
Common mistakes when interpreting it
- Measuring roughness along a ring instead of radially.
- Replacing facing with milling and keeping the roughness value but not the required lay.
- Leaving the tool retract mark at the center of a sealing face without assessing whether it breaks the requirement.
How to get it in the workshop / if it comes out of tolerance
If the face is faced on a lathe, the pattern comes out circular by nature; what you have to watch is not breaking it afterward with a touch-up or a milling pass. On a flat sealing face, continuous concentric rings usually help sealing, and that is often the reason for the requirement. Watch for the tool retract mark at the center, which breaks the pattern exactly where the drawing may not allow it.
Finish getting worse toward the center on a faced surface: constant surface speed is missing; enable constant surface speed control or limit the travel. Radial marks mixed with the circular pattern: they come from a touch-up or a poorly planned tool entry. If the drawing calls for circular and the face has been milled, the lay does not comply even though the roughness value does.
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Other symbols in Surface texture
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