rk vs turning the
l to the center
same benefit from
On my old lathe the drill bit obviously tries to center itself but
can't always overcome the handicaps of age and infirmity (the
machine's). Before reaming I run a boring bar in and usually can hear
some eccentricity and taper in the cut.
I've found combinations of chuck and tailstock position that drill
straighter than others. The best is a Collis center drill holder with
the tailstock almost fully retracted.
If your tailstock has a keying slot maybe you could pop the chuck off
the adapter and see if you can find a new position for it that
counteracts other arbor and tailstock spindle errors like droop or not
being exactly at headstock spindle height.
partially right Wes, but if the reamer is off center, it has outward
pressure on the hole as it enters and so it makes a slightly funneled hole,
plus (this is a hobby, remember) it annoys the BEEEP out of me. There may
be some additional wear on the jaws of this unit - the error is angular, not
centering - a center drill held in the chuck drills in the center of the
work, but a reamer that extends out from the chuck does not.
Jim W - there may be some combo of rearranging the chuck (which is the
biggest of the Jacob's ball bearing chucks, the one that holds 3/4 inch) on
it's JT to MT adapter that would make it better, but I doubt it. My
conclusion is "don't bother trying to fix it, get the right tool" - I'm just
trying to figure out what the right tool actually is - maybe a holder with
the rubberflex collets?
[ ... ]
As someone else posted yesterday, the chucking reamers have a
long fairly skinny shank, so even if the chuck is introducing errors,
the shank will allow the cutting forces to re-center the reamer -- as
long as you don't shorten the shank for convenience. :-)
You can probably get away without the floating holder given the
flexibility of the long shanks.
Not sure what an automotive shank is on a reamer. Perhaps
something for reaming bearings (such as ones for a camshaft) in line?
Keep asking questions and maybe we can outnumber the political
1. "automotive shank" applies to the holder, not to the reamer - it is
apparently some kind of shank used on special tools used for automotive
engine work - it is an acme thread of several diameters, one of them being 1
1/16" - for example, this one
2. so, your recommendation is to just ignore the offset and let the flex in
the reamer shaft take it up - that's what I've been doing - but it annoys
me - for those cases where I use a drill bit held in the chuck (as opposed
to a drill bit with an MT taper shank), this same offset comes into play,
and of course the larger bits (and the larger reamers) are pretty stiff.
I'd like to fix this somehow because, if nothing else, it's unaesthetic -
but I don't' want to end up with another drawer full of tooling.
I guess I don't understand those flex collets with the rubber - is the point
of the rubber to give a wide holding range or to allow some degree of
floating of the tool being held?
what about these things - I have some ER series collets and a holder for my
mill so maybe a matching holder with an MT-3 shank instead of a 40 taper
would be right?
Rubberflex collets have thin tapered metal jaws like the ones in a
Darex Drill Doctor chuck, but embedded in rubber.
The Jacobs #36 is the least accurate of my tailstock chucks because it
droops. A 3/4" drill bit in it jumps up about 1/16" when it enters a
center-drilled starting hole.
[ ... ]
O.K. A strange tool holder, with what appears to be a socket
for Morse taper holders. Whether it has a self-centering feature is
something which I can't tell just from photos. I would need it in my
That is exactly what the Jacobs Rubberflex collets are for.
Nothing to do with allowing a reamer to self-align with the hole in the
workpiece. Just an earlier idea for the same purpose as the ER collets
(and with an even wider range). They happen to be a royal PITA when
trying to chuck up something really short, BTW.
> what about these things - I have some ER series collets and a holder for my
> mill so maybe a matching holder with an MT-3 shank instead of a 40 taper
> would be right?
thanks - today, I was rearranging tooling and low and behold I have a self
centering (floating) collet chuck thingie - it is for taps - it has a tap
collet (with the square bottom) and a 3/4 inch shank - But, I don't see a
convenient way to use it to hold anything except taps, and I only have the
one collet (1/4) for it - it doesn't look like it could hold anything much
larger. So, I moved it from its previous hiding place to a new hiding
place near the taps, so at least if I need it, I have some small chance of
next step is to figure out which size ER collets I have - maybe tomorrow....
Meanwhile, I am learning something from this thread - perhaps some others
[ ... ]
Which kind of tap collet? The one used on TapMatic tapping heads
uses a small version of the RubberFlex collet -- two sizes cover all the
taps which fit that size.
Or is this the kind where you have a Morse Taper 0 adaptor to
hold a tap by the square and the shank OD?
Measure the maximum outside diameter -- in millimeters -- to get
the ER-?? number (or close to it. :-)
Hmm ... I would expect that adaptor to consume a lot of the
space between the spindle and the table. Assuming that you mean the
spindle is NMTB 40 and the colle you wish to hold is R8.
Probably a better grip than the R8 collets. They have a
reputation for letting the endmill walk down into the workpiece (and
sometimes the table) under heavy cutting loads.
The floating holder I have is W.M Zeigler Tool Co, Detroit, no numbers or
model info, 3/4 inch shank is 1.65 long, - the collet is unlike others I've
seen, steel, vaguely like a double angle collet, but with a square base so
it won't turn, and inside, it has a square section to grab the tap. I think
what I have is an early version of the 0-SA variant in the catalog that is
see page 27 for a good view of the collet - I guess I'll have to be on the
lookout for more collets too
O.K. Once I turned on enough things so it would let me *see*
to see it.
First -- this seems to be overkill for your work, and looks as
though it is for powered spindles, not non-rotating tailstock spindles.
Second -- it corrects for lateral offset, but not for angular
errors such as your drooping tailstock ram. (Assuming that it *is
If it *is* drooping, it is wear in the bore in which the ram
moves, and it will droop more the more it is extended.
However, another likely problem is wear on the carriage, so the
whole ram is below center -- whether extended or not.
The fix for the second problem (which can be verified by a Blake
centering indicator or other ways which are less convenient) is to
determine how low it is, and to add shim stock between the tailstock and
the carriage along the parting line which allows for lateral offset.
Most serious lathe makers make the tailstock just a little
*above* center, so as it wears through its life, it will get better
before it starts getting worse.
The Blake is also convenient for tuning the tailstock back on
center horizontally, too.
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. 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
[ ... ]
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
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
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.
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. :-)
Kennametal makes a double angle fully floating straight shanks holder 3/4
to 1 3/4 on the shank sizes. They use a DA180 collet to hold the reamer
shank.You can contact us at firstname.lastname@example.org or call
1-800-835-3668 for more information on these holders.
Kennametal Application Support
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