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Technical Information
Thread production with thread milling cutters
and their advantages
Thread milling is like thread cutting in that it is a chip forming With thread milling, an identical tool geometry can be
production process. A major benefit of thread milling is the applied for a multitude of materials. This considerably
size of the thread to be produced, as the cost of taps in limits the multiplicity of tools required. In contrast to thread
large dimensions can question the economic efficiency of cutting, thread milling produces a complete thread which is
the production process. Furthermore, with larger diameters virtually the total length of the applied tool.
thread cutting requires more power from the machine
tool. The possibility of machining materials with a higher Comparison of tool design between taps/thread milling
tensile strength or hardness can also be a decisive factor in cutters
choosing thread milling. In contrast to a tap, which basically consists of a single
spiral shaped tooth, the series of teeth of a thread milling
With conventional thread cutting the thread is produced cutter do not form a spiral but are configured without pitch.
from the image of the tool profile, conditional on the This fundamental difference in tool design is attributed to
chamfer lead for the workpiece. In contrast, with thread the different processes which have already been described
milling the thread is produced via a series of cutting paths in an earlier chapter.
by the milling cutter, whereby the pitch is generated by the
machine. The thread mill makes numerous passes through P
the axis section of a thread during a spiral motion in axial Tap
tool-workpiece direction and thereby interpolates the The pitch P is produced by
contour of the thread. the tap/fluteless tap.
A major factor is that cutting speeds and feed rates can T
be chosen independently of each other. Chip formation
and tool loading can be considerably influenced via these Milling cutter
setting parameters. A feature of the process is the formation The pitch P is produced
of short, comma shaped chips in contrast to thread cutting. by CNC control
circular program)
Technical To detach the chips, the direction of rotation of the machine Dimensions and cutting section measurements
spindle does not need to be reversed. The tools applied Apart from the thread pitch of the tool, the design of a thread
have a thread profile without pitch. Initially, the thread milling cutter is principally very similar to that of a tap.
milling cutter is lowered along the hole axis to the required Thread milling cutters are also characterized by dimensions
thread depth. In the approach cycle the thread milling cutter and the size of the cutting section. The thread length l2 and
is plunged to the nominal diameter of the thread. the total length l1 are also part of the dimensions.
The thread is produced by a 360 circular interpolation. The different design forms incorporate milling cutters with
Finally, in the exit cycle the thread milling cutter is radially or without collar as well as with or without countersinking
returned to the hole axis and then axially withdrawn from chamfer. The cutting section sizes of a thread milling cutter
the thread. consist of the flute length l4, the flute profile, the tooth
with Zb and the relief S. As with a tap, the flute length also
A thread milling cutter can produce threads of varying incorporates the run-out of the flutes. They do not have to
diameters (or tolerances) with the same pitch. Right- or be as large as the flutes of a tap, as this machining process
left-handed threads can be produced with the one tool. As produces smaller chips.The chips do not remain in the flutes
thread milling produces only short chips, chip evacuation during the process and do therefore not restrict further chip
does not cause any problems. development.The width of the tooth is therefore larger than
with taps. The relief grinding helps to create the clearance
angle required for milling cutters.
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