GD&T - Geometric Dimensioning and Tolerancing Profile Tolerancing Applications Questions and Answers — Questions and Answers
Question 1: A designer needs to control the form of a complex, curved surface on a casting, but its location and orientation relative to other features are not critical. Which of the following GD&T callouts is most appropriate?
- Profile of a surface with datum references A, B, and C.
- Profile of a surface with no datum references. (Correct answer)
- Position tolerance applied to the surface.
- Flatness tolerance applied to the surface.
Correct answer: Profile of a surface with no datum references.
When profile of a surface is used without any datum references, it controls only the form of the surface. The tolerance zone is established relative to the true profile, but it is free to translate and rotate. This application is ideal for controlling the shape of a feature independently of its location or orientation.
Question 2: On an engineering drawing, two separated, non-continuous surfaces must be treated as a single plane. Which is the best GD&T application to control this coplanarity requirement?
- Applying a separate flatness tolerance to each surface.
- Using a parallelism tolerance referencing a common datum.
- Specifying a profile of a surface tolerance across both features. (Correct answer)
- Controlling the distance between the surfaces with a size dimension.
Correct answer: Specifying a profile of a surface tolerance across both features.
Profile of a surface is the preferred method for controlling coplanarity. By applying a single profile tolerance to both surfaces (often indicated with a leader to a phantom line connecting them and a note like '2X'), it establishes a single tolerance zone that both surfaces must lie within, ensuring they are treated as one continuous plane.
Question 3: An engineer has specified both a profile of a line and a profile of a surface tolerance on the same airfoil feature. What is the typical relationship between these two controls?
- The profile of a line tolerance is typically larger than the profile of a surface tolerance.
- The two tolerances are always equal.
- The profile of a surface tolerance controls cross-sections, while the line profile controls the entire surface.
- The profile of a line tolerance is typically tighter than the profile of a surface tolerance. (Correct answer)
Correct answer: The profile of a line tolerance is typically tighter than the profile of a surface tolerance.
When used together, the profile of a line tolerance provides a tighter control on individual cross-sectional elements of the surface, while the profile of a surface tolerance provides a looser overall control for the entire feature. This ensures critical cross-sections maintain a precise shape, while allowing for more variation across the full length of the surface.
Question 4: A part has a complex contour defined by basic dimensions. A composite profile tolerance is applied. What is the primary function of the lower segment in the feature control frame?
- To control the location of the feature relative to the datums.
- To refine the orientation and/or form of the profile within the larger tolerance zone defined by the upper segment. (Correct answer)
- To apply a bonus tolerance based on the feature's size.
- To override the upper segment entirely, making it informational only.
Correct answer: To refine the orientation and/or form of the profile within the larger tolerance zone defined by the upper segment.
In a composite profile tolerance, the upper segment locates the profile tolerance zone relative to the specified datums. The lower segment establishes a smaller tolerance zone that refines the form and/or orientation of the profile. This smaller zone is free to float within the larger location zone but must maintain its orientation to the datums repeated in the lower frame.
Question 5: Which of the following is the key difference between Profile of a Line and Profile of a Surface?
- Profile of a Line applies only to flat surfaces, while Profile of a Surface applies to curved surfaces.
- Profile of a Surface is a 2D control, while Profile of a Line is a 3D control.
- Profile of a Line is a 2D tolerance controlling individual cross-sections, while Profile of a Surface is a 3D tolerance controlling the entire surface. (Correct answer)
- Profile of a Line must always reference datums, whereas Profile of a Surface does not.
Correct answer: Profile of a Line is a 2D tolerance controlling individual cross-sections, while Profile of a Surface is a 3D tolerance controlling the entire surface.
The fundamental distinction is dimensionality. Profile of a line defines a two-dimensional tolerance zone that controls the form of a line element at any cross-section of a feature. Profile of a surface defines a three-dimensional tolerance zone that controls the form, and potentially orientation and location, of the entire surface.
Question 6: Under which scenario can a profile of a surface tolerance be used to control size, form, orientation, AND location simultaneously?
- When applied to a feature of size with the MMC modifier.
- When applied to a surface with no datum references.
- When applied to a feature defined by basic dimensions and related to a datum reference frame. (Correct answer)
- When used in a composite feature control frame's lower segment.
Correct answer: When applied to a feature defined by basic dimensions and related to a datum reference frame.
Profile of a surface is a very powerful and versatile control. When it is applied to a feature whose geometry is defined by basic dimensions and is constrained by a full datum reference frame (e.g., A, B, C), it controls the size, form, orientation, and location of that feature simultaneously.
GD&T - Geometric Dimensioning and Tolerancing Profile Tolerancing Applications Questions and Answers
A designer needs to control the form of a complex, curved surface on a casting, but its location and orientation relative to other features are not critical.
Which of the following GD&T callouts is most appropriate?