SURFACE FINISH


Ra and Rz Values and Surface Finish Symbols


Surface finish can be indicated by measuring the surface roughness. Specifications will either be a range or a maximum average indicating the vertical deviations from the ideal surface form. A large deviation indicates a rough surface while a smooth surface will be indicated by a small deviation.

Surface roughness can be measured by the following:

Roughness Average (Ra):

Centre Line Average (CLA) is the term used by ISo for the Roughness Average of the surface finish. The Ra value measures, in micrometers or microinches, the average of all peaks and valleys indicating deviations from the mean line throughout the entire surface of a sample length. Higher values indicates a rough surface, while lower numbers indicates a smooth surface.

Ten-Point Height Measurement (Rz):

The vertical distances of the five highest peaks and five lowest valleys taken from five sampling lengths. These distances are then averaged to indicate the Rz value, measured in micrometers or microinches.

Symbols


Method.png

Any method can be used to produce the surface.


RemovalRequired.png

Removal of material is required.


RemovalProhibited.png

Removal of material is prohibited.


SurfaceTexture.png

Symbol for basic surface texture.


RaValues.png

Ra Values: microinches or micrometers


RaMinMax.png

Ra Values: maximum and minimum in microinches or micrometers


WavinessHeight.png

Waviness height rating (B): maximum in inches or millimeters.


WavinessSpacing.png

Waviness spacing rating (C): maximum in inches or millimeters.


SymbolE.png

Symbol for lay (E).


CutoffRating.png

Cutoff rating (D) or roughness sampling length in inch or millimeters.


MachiningAllowance.png

Allowance for machining (F), inches or millimeters.