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View Details. What Our Students Are Saying. Mechanical Designer. We use this characteristic for features such as the face of a part. The symbol for flatness is a parallelogram tilted to the right. The difference between the highest and lowest point of a flat surface is its flatness. The flatness symbol does not require any datums, as it only shows a tolerance range within which the whole surface of a part must conform to in 3 dimensions.
A height gauge is used for checking the results. It touches upon different areas of the surface to determine that all the points are inside the tolerance zone.
It uses 2 concentric circles on a plane perpendicular to the part axis to define the suitable tolerance range in 2D. Each point of the final measurements has to fall between the circles.
Cylindricity is basically circularity in 3D, meaning that it runs along the whole length of the part. This feature also describes other cylindrical characteristics such as its taper, straightness, and roundness. This is why this feature is also expensive to inspect. We use profile controls to control the 3D tolerance zone around the feature.
This feature helps us to give tolerance limits to advanced curves and shapes. A feature that is good for advanced curves must naturally work well with simpler curves as well. This makes profile controls extremely versatile. This is why some designers recommend abandoning all other controls and working only with profile controls. These controls form a tolerance limit around the advanced curve by mimicking it on both sides.
It then prevents any point on the feature curve from going outside the tolerance limit. Profile controls are of two types. Line profile establishes a tolerance zone around varying 2D cross-sections of the part. It controls individual line elements of a part feature. The line profile control traces the ideal curve at the tolerance limits on both sides. Surface profile control is more popular compared to line control. Instead of a two-dimensional tolerance zone, the surface profile control creates a 3D zone around a surface.
Orientation tolerance controls the orientation of a feature with respect to a defined datum. The angularity control keeps the angle of a feature with respect to the datum in check.
We can use it to control a 2D line, but it is more popular with keeping surfaces 3D under control. This kind of tight control keeps the angle and the surface flatness in check and is recommended for part features that mate with other parts through the angled surface. It is important to note that the angularity feature controls the angle indirectly, not being essentially the same as an angular tolerance e.
Rather, the necessary angle is a result of keeping to the dimensional requirements laid out by this control. Parallelism is a refined form of angularity.
There are 2 types of parallelism: surface parallelism and axis parallelism. We can choose an axis or a surface as a reference. This becomes our datum and we reference it in the 3rd block of the feature control frame as the datum for the feature.
Similarly to angularity, it does not control the actual angle but rather secures it by laying out the requirements in the form of a tolerance zone. It is a tricky control since it can mean two very different types of requirements. Surface perpendicularity specifies that a surface or line needs to be perpendicular to a datum surface or line much like angularity.
Axis perpendicularity specifies how perpendicular an axis needs to be to the mentioned datum. This is done by erecting a virtual cylinder around the target axis on a surface exactly parallel to the datum surface. There are four main types of location controls.
Concentricity, also known as coaxiality even though not exactly the same thing , control maintains the concentricity of circular as well as cylindrical features. It fixes the axis of a part to the axis of a referenced feature datum axis.
The axes of both parts are determined to be at the median points of the parts. This control can lead to some confusion because the axes derive from outside measurements, rather than their actual placement. The symmetry callout establishes a central plane around which the two parts of the feature are placed at equal distance. The midpoint of the two points on either side must lie within the tolerance zone set around the central plane. The symmetry callout is not very common. It has very limited uses and is also difficult to inspect.
We need a CMM to inspect the final symmetry. Position defines how much the actual position of a feature can vary from its intended position. The definition includes the datum plane which the measurement relates to.
We use the runout controls to measure the deviation of a part feature from its assigned position with respect to an established datum. This control is used for circular features. It essentially measures its wobble by rotating the feature about the fixed datum. Circular runout works in two dimensions to control the form, location, and orientation of various part features.
This 2D callout needs us to assign it a datum axis to check these features. Runout measures the deviation in the surface elements by rotation. Meaning that the shaft, for example, is rotated by its datum axis and the featured element is measured for tolerance. In essence, it limits the vibration of a working shaft to ensure a longer lifetime for connected parts like bearings.
Total runout is the 3D counterpart of circular runout. It controls form, location, and orientation as well. But instead of checking individual cross-sections as in circular runout , it checks the entire surface.
In all industries, the failure of the manufacturing process to meet design specifications can be problematic. This eliminates a lot of obstacles. Due to this disparity, the inspection of each characteristic requires a specific method, tool, and skill. The topics discussed in the course include Basis of Profile, Position Tolerance, Advanced concepts of profile tolerance, Patterns, Inclined Datum, Auxiliary datum, Refinement of the profile, Position controls, Simultaneous requirements, Composition position control, Composite Profile control, Slot control, Multiple Datum, Zero position tolerance, Datum targets, and Projected tolerance zone.
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