≡ Surface lay
Surface lay · Estado superficial · ISO 1101 + ASME Y14.5
Example in plan
How to interpret it
On the drawing, “Parallel lay symbol = in the direction of the view” states a surface lay requirement.
What controls
An indication of the predominant direction of the marks left on the surface by machining, expressed by a symbol placed in a fixed position on the surface texture symbol and always referred to the view in which the indication appears. It is a functional requirement, not a cosmetic one: the lay direction determines how lubricant is distributed, in which direction a seal leaks and how the surface behaves in fatigue and wear. It also determines how roughness has to be measured, because the value changes a lot depending on the direction of travel.
How to verify
The profilometer stylus must travel perpendicular to the lay, which is where the maximum value is obtained and the one compared with the drawing; measuring along the marks gives artificially good values. The direction itself is checked visually with grazing light or a magnifier, comparing against the drawing view where the symbol appears. On surfaces with crossed lay or no clear direction, measure in several directions and take the worst case.
Common mistakes when interpreting it
- Measuring roughness along the lay and getting better values than the real ones.
- Treating it as a cosmetic preference and changing the machining strategy freely.
- Interpreting the symbol relative to the part instead of relative to the drawing view in which it is drawn.
How to get it in the workshop / if it comes out of tolerance
If the drawing specifies the lay direction, changing the machining strategy is not negotiable: switching from milling in one direction to a crosshatch pattern changes the result even if the Ra comes out the same. Think about the function: on surfaces that seal by contact, continuous marks running in the direction of the leak path act as a channel; on sliding surfaces, the direction of the marks decides whether they retain oil or push it out.
If the lay obtained is not the one required, the change is in the machining strategy, not the parameters: direction of the passes, type of tool or operation (for example, grinding instead of milling). If the surface seals poorly despite meeting the roughness, check the direction of the marks before the value. And if the measurement gives very different results depending on where the profilometer is placed, you are probably measuring in different directions.
Related symbols
Other symbols in Surface texture
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