Technical Resource

We divide casting tolerances into two parts: linear and geometric tolerances

Linear tolerances

Linear tolerances refer to the distance between two points, e.g. diameter, radius, width, depth, height, center distance, etc. Generic standards use millimeters (mm) as the basic unit for dimensions. Generally speaking, when the default unit of measurement is mm. Dongying vast can meet your casting needs according to your actual situation. If you are looking for a precision casting plant for the silicone process, please contact us to discuss specific tolerance requirements.

Geometric tolerances

Geometric tolerances include shape and position tolerances. Any part is made up of points, lines and surfaces. These points, lines and faces are called elements. After machining, the actual elements of a part always have errors relative to the ideal elements, including shape and position errors. These errors affect the function of the mechanical product and should therefore be specified in the design with the appropriate tolerances and marked on the drawing according to the specified standard symbols.
Position tolerances include orientation tolerances and positioning tolerances. The details and tolerance symbols are shown in the following diagrams.

Angle Type
Normal	±1°	±2°	±2°
Premium	±0.5°	±1°	±1°
Avoid rapid changes in the structure of the casting, use rounded corners with an inner radius ≥ R0.3

Shape tolerances

1. Straightness this symbol is a short horizontal line (-) which is an index limiting the amount of change from an actual straight line to an ideal straight line. This is required for straight lines that are not straight.
2. Flatness this symbol is a parallelogram which is an index that limits the amount of change from the actual plane to the ideal plane. This is a requirement for uneven surfaces.
3. Roundness the symbol is a circle (○) which is an index that limits the amount of change from the actual circle to the ideal circle. For parts with cylindrical surfaces (including conical and spherical surfaces) in a regular cross-section (plane perpendicular to the axis), this is a circular profile requirement.
4. The cylindricity symbol is the circle sandwiched between two diagonal lines (/○/). This index is an indicator of the amount of variation that limits the actual cylindrical body to the ideal cylindrical surface. It controls various shape errors in the cross-section and axial section of the cylinder, such as roundness, straightness, straightness of the axis, etc. Cylindricity is a comprehensive indicator of the shape error of the cylinder.
5. line contour degree the symbol is convex curve (⌒), it is an indicator that limits the amount of change between the actual curve and the ideal curve. This is a requirement for the accuracy of non-circular curve shapes.
6. Surface contour degree The symbol is a semicircle at the top and a horizontal line at the bottom. It is an indicator that limits the variation of the actual surface to the ideal surface and is a requirement for the shape accuracy of the surface

Directional tolerances

1. Parallelism (∥) 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 0°, i.e., the measured element must be equidistant from the reference.
2. Perpendicularity (⊥) 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°, i.e., the measured element must be 90° from the reference.
3. Inclination (∠) is used to control the degree to which the measured element (plane or line) on the part deviates from the reference element (plane or line) by a given angle (0° to 90°), i.e., the measured element is required to be at a certain angle (other than 90°) from the reference to a certain angle.

Positioning tolerances

1. Coaxiality (◎) is used to control the angle between the different axes of the measured and reference axes that should theoretically be coaxial.
2. The symmetry symbol is the three horizontal lines in the middle. It is usually used to control the co-planar measurement elements (centre plane, centre line or axis) and reference elements (centre plane, centre line or axis) that are theoretically required. do not overlap.
3. Position degree This symbol is a circle with two lines perpendicular to each other. It is used to control the variation of the actual element being measured with respect to its ideal position. The ideal position is determined by the reference value and the theoretically correct dimension.

Runout tolerances

1. The circular runout symbol is a diagonal line with an arrow. The circular runout is the maximum and minimum reading measured in a given direction by means of an indicator in a fixed position in a given direction, the measured value being the absence of axial movement or rotational difference during one revolution of the actual element around the reference axis.
2. The full-jump symbol is two diagonal lines with arrows. The full jump is the continuous rotation of the actual element measured around the reference axis without axial movement and the continuous movement of the indicator along the ideal origin line. The difference between the maximum and minimum reading of the indicator measured in a given direction.

Limit sizes for casting holes and slots

Items	Hole Dia.(mm)	L/D
	Φ2-Φ3	L/D≤2
	Φ4-Φ7	L/D≤5
	≥Φ8	L/D≤10
	Φ2-Φ3	L/D≤1
	Φ4-Φ7	L/D≤2.5
	≥Φ8	L/D≤3.5
Deeper, more complex holes and grooves can be cast using soluble wax cores and ceramic cores.

Tolerances for flatness, straightness and roundness

Surface roughness

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