GD&T Surface Finish & Assembly Requirements 2 — Questions and Answers
Question 1: On a drawing, the surface texture symbol with a horizontal bar beneath it indicates:
- Material removal is prohibited (Correct answer)
- Material removal is required
- Any manufacturing process is acceptable
- The surface must be ground only
Correct answer: Material removal is prohibited
A horizontal bar beneath the surface texture symbol means material removal by machining is NOT permitted on that surface.
Question 2: Which Ra value represents the smoothest surface finish?
- Ra 6.3 μm
- Ra 3.2 μm
- Ra 0.8 μm (Correct answer)
- Ra 1.6 μm
Correct answer: Ra 0.8 μm
Ra 0.8 μm has the smallest average roughness value, making it the smoothest of the listed options.
Question 3: A bearing bore drawing specifies a surface finish of Ra 0.4 μm and a flatness tolerance of 0.02 mm. What is the correct interpretation?
- Only the surface finish must be met
- Only the flatness must be met
- Both the surface finish and flatness must independently be met (Correct answer)
- The tighter of the two controls the other
Correct answer: Both the surface finish and flatness must independently be met
Surface texture and geometric tolerances are independent requirements; both must be satisfied simultaneously.
Question 4: In an assembly where a gasket seals between two flanges, which surface finish parameter is MOST critical for sealing performance?
- Ra (average roughness)
- Rz (average peak-to-valley height)
- Rp (maximum peak height) (Correct answer)
- Rv (maximum valley depth)
Correct answer: Rp (maximum peak height)
Rp (maximum peak height) is critical for sealing because high peaks can puncture soft gaskets and prevent a proper seal.
Question 5: A profile of a surface tolerance applied all-around a part also controls:
- Surface finish (Ra) automatically
- Size, form, orientation, and location of that surface (Correct answer)
- Only the form of the surface
- Only orientation relative to a datum
Correct answer: Size, form, orientation, and location of that surface
Profile of a surface is a comprehensive tolerance that simultaneously controls size, form, orientation, and location when datums are referenced.
Question 6: When two mating surfaces must slide against each other under load, the designer should specify a surface finish that is:
- As rough as possible to increase friction
- Smooth enough to reduce wear but not so smooth as to cause adhesion (Correct answer)
- The same roughness on both mating surfaces always
- Determined solely by the coating applied
Correct answer: Smooth enough to reduce wear but not so smooth as to cause adhesion
Optimal tribological performance requires surfaces smooth enough to limit wear but with some texture to retain lubricant and prevent adhesive wear.
Question 7: Which symbol in ASME Y14.5 indicates that a surface must be produced by a specific manufacturing process noted in the tail of the surface texture symbol?
- A circle at the base of the check mark
- Text written in the tail/extension of the symbol (Correct answer)
- A triangle added to the symbol
- A wavy line through the symbol
Correct answer: Text written in the tail/extension of the symbol
The tail or horizontal extension of the surface texture symbol is where the manufacturing process (e.g., 'grind', 'lap') is specified.
GD&T Surface Finish & Assembly Requirements 2
On a drawing, the surface texture symbol with a horizontal bar beneath it indicates: