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CH9: SURFACE FINISH
Mechanical Engineering Department
MECHANICAL DRAWING
1
MECHANICAL DRAWINGMECHANICAL DRAWING
Chapter 9:Chapter 9:SURFACE FINISH SURFACE FINISH
MECHANICAL DRAWINGMECHANICAL DRAWING
Chapter 9:Chapter 9:SURFACE FINISH SURFACE FINISH
CH9: SURFACE FINISH
Mechanical Engineering Department
MECHANICAL DRAWING
INTRODUCTIONINTRODUCTION
The modern demands of the automobile, the airplane, and other modern machines (heavier loads, higher speeds with less friction)
need for accurate control of surface.
Not all surfaces can be finished because of cost constrains. Few surfaces requires special surface finish and should indicate on
drawing by using surface finish symbol.
The ideal surface finish is the roughest that will do the job satisfactorily.
ANSI/ASME recommended a system of surface texture symbols.
CH9: SURFACE FINISH
Mechanical Engineering Department
MECHANICAL DRAWING
3
Objectives of Machining Symbols (Finish Marks)Objectives of Machining Symbols (Finish Marks)
1. Define the surface to be machines or finished.
For die-maker a finish mark means that allowance of extra metal in the rough
workpiece must be provided for the machining.
2. Specify a particular surface finish
3. Determine the manufacturing process
Old finish marks symbol
CH9: SURFACE FINISH
Mechanical Engineering Department
MECHANICAL DRAWING
SURFACE ROUGHNESS SURFACE ROUGHNESS
Surface roughness symbols:
Surface texture symbols are used to define surface texture, roughness and lay.
Surface may be produced by any
method
Material removal by machining is required to
produce the surface
Material removal prohibited
3.5Material removal allowance. 3.5 is the amount of stock to
be removed
More surface characteristics are specified in these
spaces.
CH9: SURFACE FINISH
Mechanical Engineering Department
MECHANICAL DRAWING
SURFACE ROUGHNESS SURFACE ROUGHNESS
Application of surface roughness symbol on drawing: Normal to the surface. The point of the symbol should be directed inward toward the body metal,
not upside down. Could be vertical or horizontal as the surface, but not at any angle. Could be provided as a general note.
Symbol
00 0000
Approx. 3X
1.5X
3X
60°
Letter height = X
CH9: SURFACE FINISH
Mechanical Engineering Department
MECHANICAL DRAWING
SURFACE ROUGHNESSSURFACE ROUGHNESS
Definitions: Surface texture: includes roughness, waviness, lay and flaws. Profile: is the contour (shape) of a surface in a plane perpendicular to the
surface. Micrometer [μ] : 1*10-6 m = 1/1000000 m Roughness: small peaks and valleys found in the surface (fine irregularities) Roughness height: arithmetical average deviation [μ].
Roughness
Roughness Roughness
CH9: SURFACE FINISH
Mechanical Engineering Department
MECHANICAL DRAWING
Roughness
Roughness Roughness
SURFACE ROUGHNESSSURFACE ROUGHNESS
Definitions: Roughness width: distance between two peaks that make the roughness Waviness: larger deviation from the nominal surface on which the roughness
is superimposed Waviness height: distance from peak to valley Waviness width: distance between successive wave peaks or successive
wave valleys. Lay: directions of tool marks, or grains of surface Flaw: surface defects.
CH9: SURFACE FINISH
Mechanical Engineering Department
MECHANICAL DRAWING
SURFACE ROUGHNESSSURFACE ROUGHNESS
Location of surface specifications on surface finish symbol: Maximum values are specified
Roughness
CH9: SURFACE FINISH
Mechanical Engineering Department
MECHANICAL DRAWING
SURFACE ROUGHNESSSURFACE ROUGHNESS
Lay symbols:If it is necessary to specify the direction of the tool marks, it must be applied to the surface texture symbol:
CH9: SURFACE FINISH
Mechanical Engineering Department
MECHANICAL DRAWING
SURFACE SPECIFICATIONSSURFACE SPECIFICATIONS
Surface finish symbol (machining symbol) can be used to specify the surface finish and machining/manufacturing process.
1) Surface finish:
-is usually specified as a roughness value in micrometers printed above the finish symbol.
-The roughness value is related to the machining process. See Table.
-For more exact machining the upper and lower limits of roughness are specified.
2) Specifying process:
Could be directly specified on the finish symbol.
CH9: SURFACE FINISH
Mechanical Engineering Department
MECHANICAL DRAWING
EXAMPLES:EXAMPLES:
Application of surface texture values to symbol
CH9: SURFACE FINISH
Mechanical Engineering Department
MECHANICAL DRAWING
ADDITIONAL INFORMATIONADDITIONAL INFORMATION
Usually all information are not required. Only roughness height and machine allowance is important. In this case basic symbol is used.
Roughness height in [μm] or in [μ inch]. All other in mm or inch.
CH9: SURFACE FINISH
Mechanical Engineering Department
MECHANICAL DRAWING
EXAMPLE EXAMPLE
CH9: SURFACE FINISH
Mechanical Engineering Department
MECHANICAL DRAWING
RECOMMENDED ROUGHNESS AND WAVINESS VALUESRECOMMENDED ROUGHNESS AND WAVINESS VALUES
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