What is The Tolerance of Castings

The general casting tolerance means that after the casting of various metal castings, the measured value of the part must be regarded as an acceptable limit value. Therefore, the precise size of a casting requires a more accurate and strict tolerance.

Standard Parameters of Casting Tolerance

Main Content of Casting Tolerance

Generally, we divide the casting tolerance into two parts: linear tolerance and geometric tolerance

Linear tolerance

Refers to the distance between two points, such as diameter, radius, width, depth, height, center distance, etc. The general standard uses millimeter (mm) as the basic unit of size. Generally speaking, when the unit of size is the default, it is mm. Baisai Casting Company can meet your investment casting needs according to your actual situation . If you are looking for a solution film casting factory, please contact us. Discuss specific tolerance requirements.

Geometric tolerance

Geometric tolerances include shape tolerances and position tolerances. Any part is made up of points, lines, and areas. These points, lines, and areas are called elements. After machining, the actual elements of the parts always have errors relative to the ideal elements, including shape errors and position errors. Such errors affect the function of mechanical products, and the corresponding tolerances should be specified in the design and marked on the drawings according to the specified standard symbols

The shape and position tolerance includes the shape tolerance and the position tolerance, and the position tolerance includes the orientation tolerance and the positioning tolerance. The specific content and the tolerance symbol are shown in the following figure:

Shape tolerance

1. Straightness The symbol is a short horizontal line (-), which is an index that limits the amount of change from the actual straight line to the ideal straight line. It is a request for straight lines that are not straight.

2. Flatness The symbol is a parallelogram, which is an index that limits the amount of change from the actual plane to the ideal plane. It is a request for uneven surface.

3. The roundness symbol is a circle (○), which is an index that limits the amount of change from the actual circle to the ideal circle. It is a circular contour requirement for a part with a cylindrical surface (including conical surface and spherical surface) in a regular section (plane perpendicular to the axis).

4. Cylindricity The symbol is a circle (/ ○ /) sandwiched between two diagonal lines, which is an index that limits the amount of variation of the actual cylinder to the ideal cylinder surface. It controls various shape errors in the cross section of the cylinder and the axial section, such as roundness, straightness of straight line, straightness of axis, etc. Cylindricity is a comprehensive indicator of the shape errors of cylinders.

5. Line profile degree The symbol is a convex curve (⌒), which is an index that limits the amount of variation of the actual curve from the ideal curve. It is a requirement for the shape accuracy of non-circular curves.

6. The surface profile degree symbol is a half circle on the top and a horizontal line on the bottom, which is an index to limit the variation of the actual curved surface to the ideal curved surface, and it is a requirement for the shape accuracy of the curved surface.

Orientation tolerance

1. Parallelism (∥) is used to control the requirement that the measured element (plane or straight line) on the part deviates from the reference element (plane or straight line) by 0 °, that is, the measured element is required to be equidistant from the reference.

2. Verticality (⊥) is used to control the requirement that the measured element (plane or line) on the part deviates from the reference element (plane or line) by 90 °, that is, the measured element is required to be 90 ° from the reference.

3. The inclination (∠) is used to control the degree that the measured element (plane or straight line) on the part deviates from a reference element (plane or straight line) by a given angle (0 ° to 90 °), that is, it is required to be The measuring element is at a certain angle (except 90 °) to the reference.

Positioning tolerance

1. Coaxiality (◎) It is used to control the degree of different axes of the measured axis and the reference axis that should be coaxial in theory.

2. The symmetry symbol is three horizontal lines in the middle. It is generally used to control the theoretically required coplanar measured elements (center plane, center line or axis) and datum elements (center plane, center line or axis). Do not coincide.

3. Position degree The symbol is a circle with two straight lines that are perpendicular to each other. It is used to control the variation of the measured actual element relative to its ideal position. The ideal position is determined by the reference and the theoretical correct size.

Runout tolerance

1. The circle runout symbol is an oblique line with an arrow. The circle runout is the maximum and minimum readings measured in a given direction by an indicator with a fixed position during one revolution of the measured actual element around the reference axis without axial movement or revolution Difference.

2. The full jump symbol is two oblique lines with arrows. The full jump is the continuous rotation of the measured actual element around the reference axis without axial movement, and the indicator continuously moves along the ideal prime line. The indicator is in the given direction The difference between the maximum and minimum readings measured.