Rz Mean roughness depth Rz

Mean roughness depth Rz · Estado superficial · ISO 1101 + ASME Y14.5

Example in plan

Rz6.3onsealingface

How to interpret it

Rz limits the mean height of the most pronounced irregularities of the profile, not just the average: it is more sensitive to isolated peaks than Ra.

What controls

Mean of the maximum profile heights over a sampling length; more sensitive to peaks than Ra.

How to verify

Roughness tester with the Rz parameter and cut-off length per the cited standard.

Workshop guideline values

General: Rz on the order of 16 to 25 µm on ordinary machined surfaces.
Accuracy: Rz on the order of 4 to 10 µm on static sealing faces and close-fitting bearing surfaces.
High precision: Rz below 2 µm on fine grinding and demanding sealing surfaces.

Guidance only: the drawing's value always wins.

Common mistakes when interpreting it

Converting Ra to Rz with a fixed factor: the relationship depends on the process and the profile, and the drawing governs.
Reading Rz as the height of the single highest peak on the whole surface: it is obtained by averaging over several sampling lengths.
Looking for the cause of a high Rz in the general cutting parameters when it is usually an isolated local defect.

How to get it in the workshop / if it comes out of tolerance

If the drawing calls for Rz instead of Ra, use a roughness tester set to Rz (ISO 4287). Do not convert Ra↔Rz without a table on the drawing.

Rz penalizes isolated peaks that Ra can average out and hide: if Rz fails but Ra looks reasonable, look for a localized mark (dragged chip, tool dwell mark at the end of a pass, or a burr from an insert change) rather than a general finish problem. The same corrections as for Ra (lower feed, higher speed, larger nose radius, sharp edge) reduce Rz, but here it is also important to avoid stops or retracts mid-pass: any restart mark drives up the maximum peak that Rz measures.

Other symbols in Surface texture

√Rugosidad superficial ≡Machining direction (lay)√—Superficie a mecanizar ○ √No machining allowed =Lay paralelo ⊥Lay perpendicular XLay cruzado CLay circular RLay radial MLay multidireccional RaRoughness Ra (arithmetic mean)RqRugosidad Rq (RMS)

See the full symbol library

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