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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