Helix Angles—What Role Do They Play?
Standard end mills are offered with helix angles as low as 15° to as high as 60° angles. General-purpose end mills are generally around 30°. Any increase in the helix angle increases the effective shearing action thus reducing cutting forces and the amount of heat generated during the milling process. Chip ejection is also improved. Lower helix angle end mills are used on more difficult to machine materials where maximum edge strength and rigidity are important.
With straight flutes the load builds up almost instantaneously, making the end mills prone to self excited chatter. With helix angles, chip load is applied to the entire flute length in a progressive siding action similar to that of a snowplow with its blade angled off to one side. This makes the cutting forces much more constant with less chance for chatter. End mills with a higher helix also tend to produce much better work piece finishes. The 50° and higher helix angles significantly reduce side loading on the mill making it possible to periphery mill thin wall sections with much less deflection.
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