M Lay multidirectional
Lay multidirectional · Estado superficial · ISO 1101 + ASME Y14.5
Example in plan
How to interpret it
On the drawing, “Ra 0.2 M on polished surface” states a lay multidirectional requirement.
What controls
Lay symbol indicating that the surface has no predominant direction of marks: the pattern is roughly the same in every direction. It is the result of processes such as polishing, shot peening, blasting, vibratory finishing or EDM. Functionally it means the surface behaves in a similar way in any direction of sliding or leakage, which is usually what is wanted on bearing surfaces, decorative finishes and wherever a preferential path is undesirable.
How to verify
Roughness is measured in several directions spread over the surface and the worst value is taken: since there is no clear perpendicular to the lay, this is the only correct way to evaluate it. If the values vary a lot with direction, the surface is not truly multidirectional and the requirement is not met. The pattern is checked visually under grazing light or with a magnifier.
Common mistakes when interpreting it
- Reading it as the absence of a lay requirement rather than as a specific lay: no predominant direction.
- Measuring in a single direction and treating the value as representative.
- Accepting the pattern on a surface milled in two directions, which is a crossed lay, not a multidirectional one.
How to get it in the workshop / if it comes out of tolerance
It is not a callout meaning 'any finish will do': it is a specific lay, and it requires a process that produces it. A milled surface with visible marks does not meet this requirement even if the roughness value is correct. Keep in mind that processes such as shot peening or blasting, besides changing the texture, introduce stresses and can affect tight dimensions.
If the measurements show clear differences between directions, a dominant direction from the previous process remains: the finishing operation must be extended or intensified. If shot peening or blasting leaves the surface out of tolerance or distorted, review the sequence of operations and the intensity. And if the surface also has a fine roughness requirement, check that the chosen process can achieve it, because not all isotropic finishes are fine.
Related symbols
Other symbols in Surface texture
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