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newshound

On 13/08/2019 10:23, wrote:

Twist drills are designed for steel as a compromise between jamming risk, breakage risk & cut speed. If you steepen the angles it will cut faster but be a lot keener to jam & break. Fine on wood, but trouble on SS.

A big impediment to drilling speed is the blunt zone in the centre. If you thin that down, a twist drill drills everything a good bit faster.

NT

This is one of the "points" about high speed steel (as well as cobalt
and solid tungsten carbide). These materials retain their hardness at
red heat, at which temperature most steels have the mechanical
properties of lead. So you get frictional heating in the centre which
softens the target material here while allowing the cutting edges to do
their thing just away from the soft zone with much less local heating.