Shaft Surface and Geometry Guide｜YIXIN PRECISION MACHINERY

01

Separate surface texture from overall form

Surface roughness addresses smaller-scale profile characteristics; straightness, roundness, cylindricity and run-out address geometry or relationships. One may conform while another does not.

List size, geometrical tolerance, surface texture and appearance as separate requirements for ground or chrome-plated shafts.

02

Why an Ra number alone is incomplete

The ISO 21920 series separates drawing indication, terminology/parameters and specification operators. A reviewable requirement may also need direction, sampling, filtering/cut-off and location.

Do not assume that older and newer parameter systems are automatically equivalent. Agree the standard and edition used for the order.

03

Straightness needs a measurement boundary

For long shafts, support, gravity deflection, effective length, rotation and contact points can affect results. Tighter requirements need a clearer drawing or inspection agreement.

ISO 1101 provides the symbol language and interpretation rules, but symbols still depend on datum, scope and function.

04

A compact purchasing format

Use four lines: diameter/tolerance; function-critical geometry; surface-texture parameter and conditions; appearance, scratch protection and packing. This makes disagreement easier to trace.

STANDARDS & PRIMARY SOURCES

Trace every key concept to an official page

Links point to official ISO, ASTM or Chinese national-standard pages. Full standards remain copyrighted by their publishers.

ISO 21920-1:2021Surface texture by profile methods — drawing indication
Specifies rules for indicating profile surface texture in technical product documentation.
Open official source
ISO 21920-2:2021Surface texture by profile methods — terms, definitions and parameters
Defines terms and parameters used to determine surface texture by profile methods.
Open official source
ISO 21920-3:2021Surface texture by profile methods — specification operators
The published edition defines complete profile specification operators; a future revision is under development.
Open official source
ISO 1101:2017Geometrical tolerancing of form, orientation, location and run-out
The official ISO page lists it as current and describes the symbol language for geometrical specification.
Open official source

Questions buyers and engineers ask

01Does a brighter surface always mean a lower Ra?

No. Appearance depends on lighting, material and texture direction; acceptance requires the agreed measurement method.

02Does conforming Ra guarantee seal performance?

No. Directionality, waviness, roundness, size, materials and seal design also matter.

03Should every shaft have cylindricity specified?

No. Select characteristics from functional risk rather than adding requirements without a use case.

Apply the technical requirement to a product route

Ra, straightness and cylindricity are different shaft requirements

Separate surface texture from overall form

Why an Ra number alone is incomplete

Straightness needs a measurement boundary

A compact purchasing format

Trace every key concept to an official page

Questions buyers and engineers ask

Send the application, drawing and mandatory acceptance items.

Ra, straightness and cylindricity are different shaft requirements

Separate surface texture from overall form

Why an Ra number alone is incomplete

Straightness needs a measurement boundary

A compact purchasing format

Trace every key concept to an official page

Questions buyers and engineers ask

Apply the technical requirement to a product route

Continue with adjacent technical topics

Send the application, drawing and mandatory acceptance items.