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Differences in Tolerances Among Different CNC Machining Methods

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    We deal with CNC machining every day. Do you know the precision tolerance levels that turning, milling, grinding, drilling, can achieve respectively?

    Tolerances For CNC Turning

    Turning is a cutting process where the workpiece rotates, and the cutting tool moves in a straight or curved line within the plane. Turning is commonly performed on a lathe and is used to machine the inner and outer cylindrical surfaces, end faces, conical surfaces, shaping surfaces, and threads of the workpiece.

    The machining accuracy of turning is generally within IT8 to IT7, with surface roughness ranging from 1.6 to 0.8 micrometers.

    1. Rough turning aims to improve turning efficiency by using large cutting depths and feed rates without reducing cutting speeds. However, the machining accuracy is limited to IT11, with surface roughness ranging from Ra20 to Ra10 micrometers.
    2. Semi-finishing and finishing turning prefer high speeds and smaller feed rates and cutting depths. Machining accuracy can reach IT10 to IT7, with surface roughness ranging from Ra10 to Ra0.16 micrometers.
    3. On high-precision lathes, high-speed precision turning of non-ferrous metal parts with finely ground diamond tools can achieve machining accuracy ranging from IT7 to IT5, with surface roughness ranging from Ra0.04 to Ra0.01 micrometers. This type of turning is known as “mirror turning.”

    Tolerances For CNC Milling

    Milling refers to the process of cutting the workpiece using rotating multi-edge tools, making it an efficient machining method. It is suitable for machining planes, grooves, various shaping surfaces (such as splines, gears, and threads), and special surfaces of molds, among others. According to whether the main motion speed direction during milling is the same as or opposite to the feed direction of the workpiece, milling is further divided into climb milling and conventional milling.

    The machining accuracy of milling generally ranges from IT8 to IT7, with surface roughness ranging from 6.3 to 1.6 micrometers.

    1. During rough milling, the machining accuracy ranges from IT11 to IT13, with surface roughness ranging from 5 to 20 micrometers.
    2. In semi-finish milling, the machining accuracy ranges from IT8 to IT11, with surface roughness ranging from 2.5 to 10 micrometers.
    3. In finish milling, the machining accuracy ranges from IT16 to IT8, with surface roughness ranging from 0.63 to 5 micrometers.

    Tolerances For CNC Grinding

    Grinding is a machining method in which excess material on the workpiece is removed using abrasive grains and grinding tools, making it widely applied in precision machining in the mechanical manufacturing industry.

    Grinding is typically used for semi-finish and finish machining, with precision reaching up to IT8 to IT5 or even higher. The surface roughness in grinding generally ranges from 1.25 to 0.16 micrometers.

    1. Surface roughness in precision grinding ranges from 0.16 to 0.04 micrometers.
    2. Surface roughness in ultra-precision grinding ranges from 0.04 to 0.01 micrometers.
    3. Surface roughness in mirror grinding can reach below 0.01 micrometers.

    Tolerances For CNC Drilling

    Drilling is a fundamental method for hole machining, often carried out on drilling machines and lathes, and can also be performed on boring or milling machines.

    The machining accuracy of drilling is relatively low, typically reaching only up to IT10, with surface roughness generally ranging from 12.5 to 6.3 micrometers. Semi-finish and finish machining are commonly achieved through reaming and countersinking after drilling.

    At Ultirapid, we specialize in CNC Machining, Injection Molding, Sheet Metal Fabrication, and 3D Printing.

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