Sandvik Coromant Threading - Manual (Page 42)

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2. Applications – Thread milling
Machining with several infeed passes
Separating the thread milling operation into several infeed
passes achieves larger thread pitches and improves security
against tool breakage in diffi cult materials.
Thread milling with several infeed passes also improves
thread tolerance, due to reduced tool defl ection. This gives
greater security in long overhangs and unstable conditions.
Always calculate the correct feed required by
machine software
The feed value always depends on the h
ex
value which corresponds
with the peripheral feed rate, however many machines require a tool
centre feed (v
f
).
In internal applications, the tool path of the periphery is faster than
the movement of the tool centre line. Feed rate programming on
most milling machines is based on the centre line of the spindle
and this must be included in thread milling calculations to maxi-
mize tool life and avoid vibration/tool breakdown.
For more formulas see chapter 5, Technical reference (page 117).
Feed per tooth
To avoid feed marks on the component surface, feed per tooth
should not exceed 0.15 mm/tooth (.006 inch/tooth), therefore a
small h
ex
value is needed.