Solid-carbide thread mills allow CNC machines to generate 3-axis thread geometry with extreme accuracy. There are distinct advantages to thread milling versus tapping an internal thread.
Taps remove material by a spaced sequence of cutting edges, starting at the chamfer, that are continuously in cut. These cutting tools produce long chip formations that must be evacuated through mechanical function of the tap design. Taps also are manufactured to the dimensional size of the thread and are fully engaged with the work piece during the cutting process. This creates high cutting torque. For chip removal, tap design focuses on flute form and rake, while relief angles help to reduce cutting torque.
Thread mills form and evacuate chips and lower cutting torque. Circular thread milling is an interrupted cutting process in which material is removed by cutting “comma chips” (short, broken chips shaped like a pigtail). Short chips require a reduced space in the flute and evacuate from the cutting zone by spindle velocity and coolant pressure.
The cutter diameter of a thread mill is smaller than the minor diameter (drilled hole). This significantly reduces cutting torque because only a small surface area of the tool contacts the work. Having a cutter diameter smaller than the minor diameter allows for roughing passes, which reduces cutting torque.
Thread mills do not require a multi-tooth chamfer to optimize cutting performance. They produce a full thread to within one pitch of the bottom without degrading tool performance.
- A milled thread satisfies thread-acceptability standards according to ANSI B1.3M, for Level 21, 22 and 23.
- Full bottom threading is possible without modifying the tool.
- A standard thread mill can produce both internal and external threads as well as right and left hand threads.
- Pitch diameter can be controlled by CNC radius offset to eliminate using special oversize machine taps required for high-temperature applications that specify a 3BG-class tolerance.
- Thread mills produce optimum concentricity and perpendicularity to the minor diameter.
- One thread mill produces a variety of thread diameters for the same pitch without degrading tool performance and can be used for through and blind holes.
- High performance lubricants are not required.