SURFACEMETROLOGY

SURFACE FINISH

The designer specs Ra

Measure the surface finish

Analyze the data

to evaluate Ra

SPECIFICATION OF SURFACE FINISH

Milling

GEOMETRICAL IRREGULARITIES OF SURFACE

Waviness or Secondary Texture

Irregularities of considerable wavelength of periodic character resulting from mechanical disturbances in general set up.

Due to misalignment of centers, lack of straightness of guide-ways, non-linier feed motion

Macro-geometrical error

Roughness or Primary Texture

Irregularities of small wavelength caused by the direct action of the cutting element on the material or by some other disturbances friction, wear

Due to tool feed rate, tool chatter

Micro-geometrical error

GEOMETRICAL IRREGULARITIES OF SURFACE

METHODS OF MEASURING SURFACE FINISH

Surface inspection by Comparison Methods

Touch inspection

Visual inspection

Scratch inspection

Micro interferometer

Direct Instrument Measurements

Stylus Probe Instruments

Profilometer

Tomlinson Surface Meter

Taylor-Hobson Talysurf

Replica Methods

STYLUS PROBE INSTRUMENTS

-

PARAMETER OF SURFACE ROUGHNESS

Arithmetic mean value : Ra

AA (Arithmetic Average)

CLA (Center-Line Average)

,...

n

dcbaRa

PARAMETER OF SURFACE ROUGHNESS

Root Mean Square (RMS) average : Rq

....2222

n

dcbaRq

PARAMETER OF SURFACE ROUGHNESS

PARAMETER OF SURFACE ROUGHNESS

Maximum height of irregularity (Rmax)

The distance between two line parallel to the mean line and touching the profile at the highest point within the sampling length

PARAMETER OF SURFACE ROUGHNESS

Ten point height of irregularities : Rz

The average differences between the five highest peaks and the five deepest valley within the sampling length measured from a line, parallel to the mean line and not crossing the profile

,).()(

10864297531

n

RRRRRRRRRRRz

PARAMETER OF SURFACE ROUGHNESS(250 in) Clearance surfaces

Rough machine parts(16 in) Motor Shafts

Gear teeth (heavy loads) Spline shaftsO-ring grooves (static)Antifriction-bearing bores and facesCamshaft lobesCompressor-blade airfoilsJournals for elastomer lip seals

(125) Mating surfaces (static)Chased and cut threadsClutch-disk facesSurfaces for soft gaskets

(13) Engine cylinder borePistong outside diametersCrankshaft bearings

(63) Piston-pin boresBrake drumsCylinder block, topGear locating facesGear shafts and boresRatchet and pawl teethMiled threadsRolling surfacesGearbox facesPistong crownsTurbine-blade dovetails

(8) Jet engine stator bladesValve-tappet cam facesHydraulic-cylinder boresLapped antifriction bearings

(32) Broached holesBronze journal bearingsGear teethSlideways and gibsPress-fit partsPiston-rod bushing

(4) Ball-bearing races Piston pinsHydraulic piston rodsCarbon-seal mating surfaces

Antrifriction bearing seats (2) Shop-gage facesComparator anvils

Sealing surfaces for hydraulic tube fittings

(1) Bearing ballsGages and mirrorsMicrometer anvils

SURFACE ROUGHNESS OF MANUFACTURING PROCESSES

Courtesy of American Standards association