Page 193 - Threading_Handbook

3.10 Climb Milling vs. Conventional Milling

There are two milling methods that also apply to thread milling: conventional milling (up
milling) and climb milling (down milling). The difference between the two methods lies in the
relationship of cutter rotational direction relative to the feeding direction. THREAD MILLING

Conventional Milling (Up Milling)
Cutter rotation direction is against feed direction. The thickness of a chip increases as the
tooth of the cutter enters the material and reaches its maximal size when the same tooth of
the cutter exits the material. This method causes heat to be generated in the cut area and
a sudden heavy load on the cutter in initial contact of the tooth with the workpiece. As a
result, wear is faster and tool life decreases significantly. Chips are carried upward by the
tooth and fall in front of the cutter creating a flawed finish and re-cutting of chips.

Convetional Milling

Rotation

Chip
started zero
thickness

Feed

Climb Milling (Down Milling)
cutter direction is the same as feed direction.
Climb milling is a recommended method for all milling applications. The thickness of the chip
starts from maximum and decreases, so heat is more likely to be transferred to the chip
and not to the cutter. As a result, wear is slower and tool life increased. Chips are removed
behind the cutter, which reduces the chance of re-cutting. In this way the machined surface
stays clean and smooth.

Climb Milling

Rotation
Chip formed
max.
thickness

Feed

When to Choose Conventional or Climb Milling?

Climb milling in most cases is the preferred way for machining threads due to a lower load
on the cutter, longer tool life, and better surface finish.
During conventional milling, the cutter can dig into the workpiece and may cause the part
to be machined out of the tolerance. However, there are cases in which conventional milling
is the preferable way and even necessary. If the machine does not counteract backlash,
then conventional milling is recommended. In addition, conventional milling is preferable for
machining cast iron or hardened materials (as the cut begins under the surface
of the material).

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