On 2007-12-12, spaco wrote:
From time to time I have had real trouble sharpening SOME drill bits on
my Darex Drill Doctor. I thought I understood it pretty well.

[ ... ]

After he left, I tried to figure out why I couldn't seem to get the
Chinese bit to sharpen correctly. Finally, I realized that the back
of the "land" had less material in it than the USA bit. These Chinese
bits even feel funny when held in the hand. They feel "skinnier" in
back of the actual cutting land.
This causes the grinding angle to be off a LOT when you transfer the
bit from the locating port to the grinding port. I tried to rotate the
locating collar CCW, but I gave up after several tries and just hand-
sharpened it.

I checked several bits and see the same sort of problem, at least with
the smaller bits, but in no way do I have enough data to tell how
extensive the problem might be.

I put an image of a drill bit on my website to try to show this problem.

Go to:
http://www.spaco.org/BadDrillBits.jpg
The RED areas show where, IMO, metal is missing from the back side of
the land area.

I'd be interested to hear from others who have had similar experiences
or could shed light on the problem.

Hmm ... I do know that the settings on the tool assume a
standard helix on the drill bit. A fast spiral or a slow spiral will
not be properly aligned. And even worse, the straight flute bits which
used to come with the Yankee pump screwdrivers and drills.

The drawing of the end of the bit looks like you have a straight
flute bit, but it could simply be that it is a strangely shaped groove
in the flutes.

Good Luck,
DoN.

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