Page 194 - Threading_Handbook

THREAD MILLING A thread milling endmill is designed with annular cutting edges without helix angles. Thread
3.11 Selecting Endmill Outer Diameter for Best Effect

milling is performed when the axis of the cutter and the axis of thread direction are parallel to
each other. An incompatibility in the direction of the cutting edges with the threading direction
causes geometrical distortions during thread machining. The geometrical distortion of the
thread profile increases as the thread pitch increases and the endmill diameter increases,
which can be explained by an increase in the contact angle of the endmill with the workpiece.
Therefore, if the endmill diameter is smaller, then the thread profile is more accurate.

Small Tool Diameter Large Tool Diameter

Geometrical
distortion Geometrical
distortion

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