Helical milling video courtesy Makino
A machining center able to maintain precise control at high feed rates makes it practical to machine holes through helical milling as an alternative to drilling.
The same speed permits faster drilling, too, so helical milling won’t necessarily be the best approach. Here are applications where helical milling is likely to make sense:
For chip ejection problems
Compared to drilling, helical milling makes it easier for chips to clear the hole.
Various hole sizes
Where there are different-sized holes in one part, helical milling can save on tool change time by letting one tool mill multiple diameters.
Holes initially formed through casting can be rounded and straightened through milling more easily than through drilling.
Compared to tapping, helical milling can place threads more accurately, and it can thread a shallow hole more easily. Certain combination tools can also machine threads in the course of machining the hole itself, thereby eliminating a tool change.