CH9: SURFACE FINISH

Mechanical Engineering Department

MECHANICAL DRAWING

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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

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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

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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

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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

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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

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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

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MECHANICAL DRAWING

SURFACE ROUGHNESSSURFACE ROUGHNESS

Location of surface specifications on surface finish symbol: Maximum values are specified

Roughness

CH9: SURFACE FINISH

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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:

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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.

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EXAMPLES:EXAMPLES:

Application of surface texture values to symbol

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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.

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EXAMPLE EXAMPLE

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RECOMMENDED ROUGHNESS AND WAVINESS VALUESRECOMMENDED ROUGHNESS AND WAVINESS VALUES