I am going to be taking the spindle out of my Sheldon for some repair
work and want to make sure I set the bearings back up properly. The
procedure I have always used when setting preload on tapered spindle
bearings is to rotate the spindle by hand wile tightening the bearing
collar and then when it just slightly drags back off the collar by
1/4- 1/6th of a turn so the bearings can expand when thay heat up and
do not gall and remove the end play from the spindle.
The manual is vague but just state to remove all end play in the
spindle when reassembling. This sounds like it could cause problems. I
believe that you need at least a small amount of end play for oil
circulcation and as I stated earlier for heat related bearing
expansion. With both of these combined, oil circulation around the
bearing and thermal expansion end play should be removed after the
bearings warms up. Is this a true assumptuion? Thanks, Steve
Hummm good question. What I would do..and its worth exactly as much as
you paid for it..would be to hand snug it. then run it for 30 minutes
at mid speed. Then put a dial test indicator on your carraige, and
indicate the nose in the Z axis (parallel with the bedway)..then get
somone to really push and pull on the spindle, and tighten or loosen
until you have less than .001 to .0005 backlash. This should do it
as you are checking it when its warm and the bearings are expanded.
Id be curious as to what the backlash will be after the lathe has
cooled to ambient.
That rifle hanging on the wall of the working-class flat or labourer's
cottage is the symbol of democracy. It is our job to see that it stays
- George Orwell
you can get bearing standards from the bearing manufacturers
when we rebuild equipment at the shop we measure the total clearance between
the roller and race at the top of the bearing and use a bearing manufacturer
supplied chart to determine how much to tighten , usually a percentage of
Sounds like a good plan to me, but I'd adjust for zero
clearance either at temp or cold, and stick with the
tighter setting. Then run for another hour keeping a close
watch on temperature. Prying on the spindle with a 2x4
should work as well as applying an axial force - unlike a
ball bearing, there's a direct relationship between axial
and radial play in a tapered roller bearing.
The spindle will be hotter than the head casting when
things warm up. Whether the preload is higher hot or cold
will depend on whether the bearings are mounted cups in and
cones out, or vice versa.
I just went back and reread the OP. I first assumed that
the lathe has roller bearings, but that's not clear to me
now. Gunner's advice is probably better if we're talking a
tapered plain bearing.
The CTE difference between the spindle and head casting is very small,
the distance between the bearings relatively small, and the temperature
change is relatively small. Set for ZERO clearance, run it for several
minutes at high speed, check for excessive heating.
Most lathes are set up so the preload DECREASES when the spindle
heats up. The spindle is going to get hotter than the headstock
casting, and there is often quite a length between the two bearings.
Since you mention tapered roller bearings, they sound like they are
at opposite ends of the spindle, is that correct? Is this a
geared-head or belt-drive lathe? If it is a geared-head or
otherwise an oil-filled headstock, it won't heat much at all.
This was posted in the Yahoo group on 9 x 20 lathes in the files
section: (sorta long but worth reading)
Called Emco in Austria about 3am (my time one night) and got
connected with an english speaking engineer who told me how to check
tension on ALL gearhead Emcos of the era. The method (he said) they
use in the factory; "With the machine in neutral, disengaged from
lead or hex screw (if applicable), and either the 3 or 4 jaw chuck
installed, spin the chuck by gripping one of the opened jaws on top
of the chuck and spin strongly. One revolution of the chuck is
perfect. Less is too tight or bad bearings and more than 1.5
revolution is too loose. I've used it ever since and it's an
excellent yardstick that hasn't failed me yet. My new S11CD spins
1/2"-3/4" past one revolution and that old one would only spin about
3/4 of a turn until I re-adjusted it. Apparently a "little" too tight
is a LOT too tight.
Due to the number of emails I've gotten last night and this morning I
thought I'd clarify this procedure.
First, it's done on a cold machine rather than one thats up to
operating temp. When Emco checks theirs they are not fully assembled
or at a place where power can be introduced to the machine and so
they do the pre-load cold.
When spinning the chuck I locate (or make) a mark on the chuck near
one of the jaws or note the number of the jaw I'm using to spin the
chuck. I rotate the chuck so that the jaw I'm going to use is at the
2 o'clock position when viewed from the tailstock end of the lathe.
When spinning the chuck by hand you'll notice that this releases the
jaw from the spinning finger at approx the 8 o'clock position,
sending the chuck on around. What you want is that jaw to end up, on
it's own inertial free-spin back at the 8 o'clock position or close.
A little over-rotation is preferrable to being short of the mark. If
you can't get it past 1/2-3/4 turn with lots of effort it's
definately too tight and if it spins more than 1.5-2 revolutions you
could probably use a a little snugging up.
In my original post I said give it a "strong" spin and should've said
a comfortable, firm spin. As in one that you can easily duplicate
several, or even many times without causing pain or discomfort on the
spinning finger. Just a comfortably firm, easily repeatable spinning
action that you could repeat all day long if you had to.
And while I originally got this advise from Emco on a lathe using a
4" chuck I've used it on lathes up to and including 6" chucks. I have
no idea if due to inertial loads it's applicable to 3" chucks or 8"
but I would assume so tho it would take a correspondingly
lighter/heavier spin to achieve the desired result.
I think the most important thing to determine a safe, proper pre-load
is that the chuck/spindle assembly isn't binding or dragging and that
it's not completely free-spinning either. If it's too tight it's
fairly obvious very quickly. If it's too loose you can probably
measure a little end play at the chuck by pulling/pushing on it. For
reference my chuck indicates .0000" end play cold, when
pushing/pulling by hand against a test indicator.
An additional point of reference is if I spin my S11CD chuck as hard
as I can with a rag beneath my finger on the spinning jaw to cushion
it my chuck will spin right at 2.25 revolutions. But in normal
comfortably firm checking it only spins a hair past one revolution.
Hope this helps to define the ambiguity of terms like "comfortable or
Sorry to all the people I kept up last night or caused to get up
early this morning to go out, start spinning their chucks. Tho
admittedly I'm a little amused by the visual.
Your visual may be accurate. I was spinning my chuck this morning
before anyone else awoke and before the dog got fed. This maximat 7
(the yellow one in photos) spins like a perpetual motion machine. I
have much chatter on heavy cuts and have tried everything (gibs,
cutter overhang, locked compound, etc.). The spindle preload was
going to be next and your post gave me the incentive to go and try
it. I didn't realize just how bad it was. FYI, I had measured end
play and it bearly moved a 0.0005" indicator.
Mance just gave me a new lathe with his suggestions for testing
preload of the spindle bearings and acceptable limits. My maximat 7,
while giving a pretty good finish, could not take deep cuts without
serious chatter of the entire lathe and base no matter what else I
The spindle would give many revolutions after a quick spin by hand as
Mance suggested. I tightened the preload until only about one
revolution was produced. I was then able to take 0.150" depth of cut
on 1" CRS, and as hard as I could feed by hand (brazed carbide tool,
positive rake). The chips looked like an ad for Iscar.
Tapered roller bearings in general are more tolerant of zero
clearance, or even true preload, conditions. I think the OP's
approach of measuring spindle drag is pretty good, that's how
the manufacturer does it.
Another way would be to do that same thing a bit more
scientifically by measureing breakway torque on the spindle.
Wrap a string around the chuck, and connect the end to
a spring scale.
Then measure how much tangential force is required to
force the chuck to spin. The more the preload, the larger
the force. This will be a bit more repeatable than the
"one turn spin" method.
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
It has been years since I read about bearings, but as I remember
preload means the amount of additional tightening of the bearing AFTER
ALL SLOP HAS BEEN REMOVED. Without checking a book on bearings, I
would remove all clearance, run it to get it warm, and then adjust to
remove all clearance and tighten it a 1/16 th to 1/8 th of a turn
more. Then run it some more and see if it gets hot.
I have always used when setting preload on tapered spindle
Is this a true assumptuion? Thanks, Steve
The procedure from the factory for replacing the tapered bearings in
one of my CNC lathe headstocks involves a preliminary tightening of
the adjustment nuts until you get a certain amount of Z axis endplay
with a certain amount of end force on the spindle.
Then run the spindle at a low rpm for an hour or so. Check
Adjust nut for less endplay. Run again at higher rpm while watching
Repeat the above steps until you get a situation where there's only
.0002" endplay with a certain end force on the spindle and the machine
will run continuously at 4000rpm without overheating the spindle.
To follow their exact procedure will take at least a full day or more.
Technically this is correct. In common use however you will
see folks talking about "preload" where they really mean
'get the clearance down below some certain level' even
though there is still some positive number that represents
the clearance. It's not zero, and it's not negative. But
they still say 'preload' where that term really should
be used to describe the case where the clearance number
has gone below zero.
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
As others have replied, at least in a rigid setup - massive cast
headstock - you need to deal with the temperature expansion
coefficient and make sure the preload isn't too high when cold or hot.
Presumably cold for a typical lathe.
That said, I experimented with the spindle bearing preload on a
Grizzly 12" gear head lathe I used to own. While the headstock was
cast iron, it was just a lightweight square box, with fairly thin end
walls that supported the taper roller bearings at each end of the
What I learned is that the headstock casting was so flexible, you
could tighten the bearing far beyond where it took up the free play,
and it just pulled in the outboard wall of the headstock, without
increasing the drag on the spindle by much at all.
So I figure for this class of machinery, maybe there is a different
approach - take up the preload entirely and let the casting function
as a large spring, that maintains fairly contstant tension on the
bearing with no free play over the full temperature range. If you
Sheldon is like this, I have no idea. Perhaps not.
I'd like to know if this is a deliberate aspect of the design of a
machine with a lightweight casting like this one.
As far as I can tell, the spindle on my 13" Sheldon has never been
messed with. It has a surprisingly high breakaway torque. In fact,
it's a PITA when dialing in something in the 4-jaw.
When I installed new bearings in my 11" Sheldon I stopped short of
preloading them that much. For all practical purposes I have zero
runout on the spindle no matter whether the machine is idle and cold
or in use and warmed up.
IIRC, I tightened the 11" bearings until I could feel a drag on the
spindle, then backed off just a smidgen. I don't know if it's the
correct way to do it, or not, but it seems to be working well.
BTW, I've gotten into the habit of *always* checking the level in my
Sheldons' oil cups before starting the machine each day. The castings
are porous enough to allow the oil to slowly seep out.
I had noticed that one of the engineers at work has a book on
bearings, so I borrowed it and read up on preload. I also googled a
bit and found some stuff by Timken and another bearing manufacturer (
I think it was SKF ). Anyway all the data I have says that a slight
preload ( tightening after all the clearance is removed ) will give
the longest bearing life more than with zero clearance or some slop.
It will also greatly increase the rigidity of the spindle.
Preload does two things. One on roller bearings is change the contact
from a point to a line contact. Second it causes all the rollers to
contact the cups, not just the ones on one side. Now when you put a
radial load on the bearing, the load on the other side decreases while
the load on the other side increases.
So you have at least twice the spring constant of the case where you
have just zero clearance.
But do not over do the preload. A little more preload causes the
tempertures to rise and the life to drop rapidly.