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Tolerance of shape and position in machine processing

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Tolerance of shape and position in machine processing

Definition of shape and position tolerances

The geometric characteristic of a part refers to the deviation between the actual element of the part and its geometric ideal element. It includes the deviation of size, the deviation of the shape, direction or position of the geometric elements of the part, surface roughness, surface waviness, etc.

Shape and position tolerance, also known as geometric tolerance, is used to control the deviation of the actual shape, direction and mutual position of each element on the part from the ideal shape, direction and mutual position. In order to ensure the geometric accuracy of the shape and position of the part. The geometric accuracy achieved by the control of the various indicators of the form and position tolerances ensures and improves the working performance, working accuracy, life, reliability, and economy of manufacturing costs of parts and products.

1. Straightness
Straightness, which is commonly referred to as the degree of flat, indicates that the actual shape of the linear elements on the part maintains an ideal condition of straight line. Straightness tolerance is the maximum amount of variation allowed by the actual line to the ideal straight line.
2. Flatness
Flatness, which is commonly referred to as the degree of flatness, represents the actual shape of the plane elements of the part, and maintains the ideal plane condition. Flatness tolerance is the maximum amount of variation allowed by the actual surface to the ideal plane.
3. Roundness
Roundness, which is commonly referred to as the degree of roundness, indicates that the actual shape of the element of the circle on the part is kept equidistant from its center. The roundness tolerance is the maximum variation allowed by the actual circle to the ideal circle on the same section.

4. Cylindricity
Cylindricity means each point on the contour of the cylindrical surface of the part, and the axis is kept equidistant. Cylindricity tolerance is the maximum amount of variation allowed by the actual cylindrical surface to the ideal cylindrical surface.
5. Line Profile
Line profile refers to the condition of maintaining the ideal shape of the curve of any shape on a given plane of the part. Line profile tolerance refers to the allowable variation of the actual contour of a noncircular curve.  
6.Surface Profile
The surface profile is the condition that the curved surface of any shape on the part maintains its ideal shape. The face profile tolerance refers to the actual contour line of the non-circular curved surface, and the allowable amount of change to the ideal contour surface.
7. Parallelism
Parallelism, which is commonly referred to as the degree of parallelism, indicates that the actual elements on the part are kept equidistant from the reference. Parallelism tolerance is the maximum amount of variation allowed between the actual direction of the measured element and the ideal direction parallel to the reference.
8. Perpendicularity
Perpendicularity, that is, the degree of orthogonality between the two elements that is commonly referred to, indicates that the measured element on the part maintains the correct 90° angle with respect to the reference element. Perpendicularity tolerance is the maximum variation allowed between the actual direction of the measured element and the ideal direction perpendicular to the reference.
9. Inclination
Inclination is the correct condition that the relative direction of two elements on the part maintains any given angle. The inclination tolerance is the maximum variation allowed between the actual direction of the measured element and the ideal direction at any given angle to the datum.
10. Position degree
The position degree indicates the accuracy of points, lines, areas and other elements on the part relative to their ideal positions. The position tolerance is the maximum allowable variation of the actual position of the measured element relative to the ideal position.
11. Concentricity
Coaxiality, which is commonly referred to as the degree of coaxiality, represents the condition that the measured axis of the part remains on the same straight line with respect to the reference axis. Coaxiality tolerance is the allowable variation of the measured actual axis relative to the reference axis.
12. Symmetry Control
Symmetry control refers to the state that the two symmetrical central elements on the part remain in the same central plane. Symmetry control tolerance is the allowable variation of the symmetry center plane (or center line, axis) of the actual element to the ideal symmetry plane.
13. Circular Runout
Circular runout means that the revolving surface on the part maintains a fixed position relative to the reference axis within a defined measurement plane. The circle runout tolerance is the maximum amount of variation allowed within the limited measurement range when the actual element to be measured rotates a full circle around the reference axis without axial movement.
14. Total Runout
Total runout refers to the amount of runout along the entire measured surface when the part rotates continuously around the reference axis. The total runout tolerance is the maximum runout allowed when the measured actual element rotates continuously around the reference axis while the indicator moves relative to its ideal contour.


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