Gary May inquired:

>I've been puzzled for years on how (and why) they do that
>solid-center auger. I have several sets of vintage Irwins and some solid-center
>bits in large diameters made recently with bitstocks *designed* to be sawn off
>if desired (revealing a hex shank)  but I still don't get the concept.  The
>drawn-out and twisted rod seems perfectly adequate and super-simple.

I know enough about how things are made to be aware of my ignorance and avoid
making wild guesses. As to the why, I am not similarly encumbered. SO, my
thoughts on the why:


1) chip clearance (single flute types)- The solid center I have are all single
flute (On those with a second cutting edge, the second ends after one turn or
so). I know there are other types, but these clear chips very well.

b) The core adds stiffness. It any point along a twisted bit, the thin way is
very thin, and the bits do flex a fair bit. I would guess that the solid core
are also more resistant to wind-up due to the additional axial strength. With a
brace, the flex in use can be annoying, and with a modern powered drive (I don't
have one at home, but at an old job we powered the larger machines with flat
belts), the wind-up can be significant. When they wind-up enough, twisted bits
tend to do the 'phone cord' thing and knot up.


Yup. 
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