8-7: Surface Texture
Designers must accurately describe
the required finish to the people
actually making the parts.
Two principal reasons for surface finish
control:
• To reduce friction
• To reduce wear
Surface Texture Characteristics
• Microinch: μin is one-millionth of an inch
(.000 001 inch)
• Micrometer: μm
• Roughness: consists of the finer irregularities
in the surface texture, usually including those
that result from the inherent action of the
production process.
• Roughness-Height Value, roughness spacing,
roughness width cutoff, waviness, lay, flaws
Surface Texture Symbol
• Roughness, waviness, and lay may be controlled by applying the desired
value to the surface texture symbol, in a general note, or both.
• The point of the symbol should be located on the line indicating the
surface, on an extension line from the surface, or on a leader pointing to
the surface or extension line.
• When numerical values accompany the symbol, the symbol should upright
and readable from the bottom
• When no numerical values accompany the symbol, the symbol can be
positioned to be readable from the right side.
• For plain surfaces, the surface texture symbol refers to the completed
surface
• For plated or coated surfaces the designer must indicate if the surface
texture value applies before, after, or both the plating or coating
Surface Texture Ratings
1. Indicated to the left of the long leg of the
symbol
– One rating gives maximum value
– Two ratings indicates maximum and minimum
values
2. Waviness-height rating is located above the
horizontal extension of the symbol
3. Waviness-spacing is separated from the
waviness-height rating by a dash
4. Lay symbol located to right of long leg of
symbol.
Machined Surfaces
• Cast, molded, or forged parts need symbols to
indicate machining or finishing.
• FINISH ALL OVER may be used as a general note.
• √ is the symbol for surfaces produced by machining
operations
• Material removal allowance (amount of material to
be removed) is shown in inches or mm to the left of
the symbol
• Material removal prohibited is shown by a special
symbol