Sandvik Coromant Threading - Manual (Page 39)

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2. Applications – Thread milling
Choice of cutting diameter
The cutter engagement will create a minute form error on the root
of the thread profi le. In internal applications, the relationship be-
tween threading diameter, cutting diameter and pitch will affect the
true radial depth of cut, a
e
eff, which becomes much larger than the
chosen radial depth of cut. A larger true ae will increase the devia-
tion in the root of the thread.
To minimize the profi le deviation, the cutter diameter should be no
greater than 70% of the threading diameter.
Ex M30x3
Dia 21.7 gives a profi le deviation of
0.07 mm (.0027 inch)
Dia 11.7 gives a profi le deviation of
0.01 mm (.0004 inch)