Page 195 - Threading_Handbook

At the same time, a larger endmill diameter usually causes bending stiffness and this
enables a more stable machining process such as: thread milling with high overhang, better
resistance to vibrations, etc. A large tool diameter can significantly improve productivity as it
allows machining with hard cutting conditions.

Accordingly, to improve the thread milling process it is necessary to increase the diameter of THREAD MILLING
the tool while taking into consideration the restrictions of the thread profile accuracy.

d < D
Δyd > ΔyD
y y y y
L L F F
L L F F
d d x x D D x x

∆y
∆y D D
∆y
∆y d d

L- Tool overhang
F-Bending force
D;d=Tool diameters
Δy=max. deflection in bending

Based on the analysis performed of selecting initial outer diameter of the endmill, the
following conclusions can be assumed:

• For internal thread milling, in most cases the initial endmill diameter is recommended to be
up to 70% of the thread major diameter.

• For external thread milling, in most cases the initial endmill diameter can be over 70% of the
thread major diameter.

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