The cylindricity is the point on the outline of the cylindrical surface on the part, and the axis is kept equidistant.
Cylindricity is an indicator that limits the amount of variation of the actual cylinder against the ideal cylindrical surface. Its tolerance band is the area between two coaxial cylindrical faces with a tolerance value of t as the radius difference. It controls the shape tolerances of the cylindrical cross-section and the axial section, such as roundness, straightness of the axis, straightness of the prime line, etc. Generally speaking, It no need to mark the roundness and straightness while indicating the cylindricity. If the roundness and straightness must be marked separately, the tolerance must be less than the cylindricity tolerance, this is to indicate that the design has further requirements for radial or axial shape tolerances.
Usually, the cylindricity error is detected by a roundness meter or a computer-equipped coordinate measuring device. If without this device, Better use parallelism of the circularity and the cylindrical surface line instead of using cylindricity.
When you use roundness and parallelism instead of cylindricity, the roundness tolerance value and parallelism tolerance value should be determined according to the aspect ratio of the cylinder.
• When the cylinder length is greater than its diameter, the linear parallelism tolerance value must be greater than its roundness tolerance value. • When the length of the cylinder is equal to its diameter, the parallelism tolerance value of the prime line and its roundness tolerance value should also be equal too. • When the length of the cylinder is less than its diameter, the tolerance of the parallelism of the plain line must be less than the roundness tolerance value.