On 2008-10-27, haryt wrote:
I have a selection of large MT2-3 HSS drill bits that I would like to
shorten (to remove the MT) and turn down to approx 13mm diameter to
fit in my lathe tailstock chuck. Is this feesable? How easy will the
material be to turn on my lathe?

Before you consider this -- I have a question:

What is the taper of your tailstock ram?

If it is MT-3, then you use the larger bits directly in it, and
use the smaller ones in a MT-2 to MT-3 adaptor sleeve. This will give
you less projection (which eats distance between headstock and
tailstock) than the modified bits in a chuck large enough to hold them.

If it is MT-2 -- use the smaller ones directly in the tailstock,
and use a step-up sleeve to fit the MT-3 drills in the MT-2 tailstock
ram. This *will* eat distance -- but will still be better.

Large drill bits with reduced shanks tend to slip in chucks.
You can buy them in sets -- called "Silver & Demming" bits. (I'm not
sure of the spelling of the second word.)

If your tailstock does not have a Morse taper at all, I guess
that you will have to do this, but plan on setting up in a milling
machine with a dividing head and milling three flats on the reduced
diameter shank at 120 degree intervals to help control the slip -- at
last in the drill chuck's jaws -- though it may still slip at the Jacobs
taper fit from the arbor to the drill chuck.

And while the working end of drill bits tends to be hard tool
steel of some form or other, the shanks are usually a much softer steel.
Just look at the shanks of bits which have slipped in drill chucks --
they will be grooved and there will be parts projecting up which have
been wiped. And if this happens in the smaller bits, just think how
likely it is in the larger bits.

Good Luck,
DoN.

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