On 2010-05-09, Bill Noble wrote:


However, another likely problem is wear on the carriage, so the
whole ram is below center -- whether extended or not.

[ ... ]

Thanks Don - In my case, I know that it is the drill chuck, not the
tailstock - an MT drill or reamer put into the quill directly aligns
accurately (well, within a few thousandths), a drill blank held in a collet
aligns accurately also, as does a live center - but a drill rod or a reamer
held in the Jacob's chuck is misaligned.

Hmm ... does the tailstock ram engage the tang, or can you
rotate the arbor (and the chuck with it) to any possible position?

You might see what the drill rod does with the Morse taper arbor
rotated 180 degrees.

Second -- it is possible (especially if you have an old chuck
and arbor) that the arbor has been bent by crash. When I get chucks
via eBay, even if the come on the right sized arbor, I buy a new arbor
from MSC -- either Jacobs brand, or Albrecht -- so I don't have to deal
with a bent or poorly made arbor.

Hmm ... also -- do you have a Morse taper gauge for that taper?
If so -- blue the arbor and trial fit it into the gauge to see whether
it is making full contact. It might have a ding which is causing it to
fit off center, and you can simply stone off the ding until you get full
contact around the arbor (except where you have stoned too deep, of
course. :-)

Usually, drill chucks are a lot better than the specs say,
especially the high end Jacobs and the Albrecht ones. Those specs say
that it won't be *worse* than this -- not that every one will be this
bad. :-)

Hmm ... also, how good are the jaws in the chuck? A drill
spinning in the chuck (e.g. trying to use a Silver & Demming 1" drill
bit without shank flats in a 1/2" chuck) can damage the jaws of the
chuck as well as the shank of the bit.

You can get rebuild kits from Jacobs (if a genuine Jacobs
chuck), and you can find instructions on the Jacobs web site if you have
never taken a chuck apart before. Before you start, you will need to
make two sleeves on your lathe -- one for pressing the chuck apart, and
the other for pressing it back together. Aluminum works fine for this,
and you need a different set for each size of chuck. You also need an
arbor press of some sort.

The reason I went down the path of
getting one of these floating holders in the first place was that I couldn't
see a practical way to hold a range of chucking reamers without a chuck, and
if chucks aren't accurate, then I need the float - did I go off track with
this reasoning?

I think that it is overkill in this case. Your consideration of
the ER collet chuck in the tailstock should work quite well --
especially since your other collets and such have tested good. You
don't need a standard drill chuck to hold a chucking reamer -- but you
*can* use one if that is what you have -- and the chuck and arbor are in
good condition. It is called "chucking" to distinguish it from the ones
with flats on the end for a tap wrench. :-)

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---