Subject: Lathe Headstock Bearings

From: [email-masked] (Tom Herbert)
Date: Tue, 17 Sep 1996 15:49:50 GMT

I have an Atlas/Craftsman 12" lathe of about 1960's vintage.  After
tightening every nut, bolt and belt on the machine, I was still
getting a strange set of toolmarks on each turned piece.  They are
diagonal hills and valleys that cross the regular toolmarks at about
30 degrees.

After doing everything else that I and all of my machinery-inclined
friends could think of to do, I finally took the headstock apart, and
cleaned the bearings.  Then I noticed that the front bearing (closest
to the chuck) had evidently overheated at some point in the past;
both the inner and outer races had heat discoloration rings, and there
was baked-on oil on the ends of the rollers.  There was also paint
chips in both of the bearings from the restoration that was done to
the lathe before I bought it.

After reassembly, the lathe runs much more quietly than it did before,
but still makes these strange toolmarks--although admittedly not as
pronounced as before.

I would like to replace the bearings on the spindle, but there are two
classes of bearings available, standard and class 3.  The standard
bearings are about $98.00 for the four pieces (2 cones and 2 outer
races), and the class 3 are about $280.00.

Does anyone know what type of bearings (what class) are generally in a
lathe headstock?  I would obviously prefer to spend less money if the
class 3 bearings will not add anything to the lathe.

Thanks for any help in advance.

Tom Herbert
[email-masked]

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From: [email-masked] (Jonathan M. Elson)
Date: 17 Sep 1996 18:25:37 GMT

Tom Herbert ([email-masked]) wrote:
: I have an Atlas/Craftsman 12" lathe of about 1960's vintage.  After
: tightening every nut, bolt and belt on the machine, I was still
: getting a strange set of toolmarks on each turned piece.  They are
: diagonal hills and valleys that cross the regular toolmarks at about
: 30 degrees.

: After doing everything else that I and all of my machinery-inclined
: friends could think of to do, I finally took the headstock apart, and
: cleaned the bearings.  Then I noticed that the front bearing (closest
: to the chuck) had evidently overheated at some point in the past;
: both the inner and outer races had heat discoloration rings, and there
: was baked-on oil on the ends of the rollers.  There was also paint
: chips in both of the bearings from the restoration that was done to
: the lathe before I bought it.

: After reassembly, the lathe runs much more quietly than it did before,
: but still makes these strange toolmarks--although admittedly not as
: pronounced as before.

: I would like to replace the bearings on the spindle, but there are two
: classes of bearings available, standard and class 3.  The standard
: bearings are about $98.00 for the four pieces (2 cones and 2 outer
: races), and the class 3 are about $280.00.

I replaced the bearings in my 10" Atlas when I got a used roller bearing
headstock to replace the absolutely shot babbit journal headstock it
came with.  After I found out the bearings were only about $30-$38 each
(both pieces) it just seemed the best policy to replace them before all
the reassembly and aligning.  You should check with the local bearing
distributor, ie. IBT, Bearings, Inc. or one of the similar outfits.
They may have the standard bearings at a better price than you can get
it for from Clausing.

Now, the class 3 bearings may be ground to a better TIR tolerance, but
I don't think there is a big difference otherwise.  If you re-grind
your chuck jaws on the machine, then the error caused by the cheaper
bearings may not show up at all.  I waited to regrind my jaws until
the new headstock was i place.  (By the way, I got replacements of the
bearings by exact part number match, but I don't know whether you can get
different accuracy classes in the same part number.)

I have gotten excellent results with the new bearings I got from IBT.
Total cost was something like $72 including taxes, for 2 inner races
with rollers and 2 outer races!

Just one final note - if the races and rollers appear smooth, your surface
finish problem may be inadequate preload, rather than shot bearings.
On the 10", you are supposed to run the lathe for 2-8 hours at 'moderately
high speed' to get the spindle warmed up (it expands .004" or so) and
then tighten the compression nut on the end of the spindle until 'slight
drag' is felt, and then tighten one gear tooth further.  With the spindle
cold, this causes the headstock housing to be under load, pulling outward
on each outer bearing race, and keeping the bearing rollers loaded on the
races.  If the preload is not set right, the spindle will have the loosenenss
to do exactly what you describe.  The preload procedure for the 12" may
be slightly different in the specifics, but is probably similar.
Anyway, it doesn't sound too critical, as they depend on such precise
measurements as 'moderately high speed' and 'slight drag'!

When setting preload on a differential pinon, I've seen specs for using a
torque wrench (in-oz range) to tell when the 'slight drag' is just right.
But they don't get so specific in my Atlas book.

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From: [email-masked] (Steve Rayner)
Date: Thu, 19 Sep 1996 08:33:55 GMT

Probably the expensive ones are best.  You are paying for a close fit, 
and accuracy.

In a previous article, [email-masked] (Tom Herbert) says:

>comm.net!usenet
>From: [email-masked] (Tom Herbert)
>Newsgroups: rec.crafts.metalworking
>Subject: Lathe Headstock Bearings
>Date: Tue, 17 Sep 1996 15:49:50 GMT
>Organization: Access Communications, Inc. ( Houston, TX ) 
>Lines: 33
>Message-ID: <[email-masked]>
>NNTP-Posting-Host: 206.97.162.100
>X-Newsreader: Forte Free Agent 1.0.82
>

-- 
Steve.

**************  BE ALERT, THE WORLD NEEDS MORE LERTS ************************

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From: "John Nicol" <[email-masked]>
Date: 19 Sep 1996 00:59:24 GMT

Tom Herbert <[email-masked]> wrote in article
<[email-masked]>...
> diagonal hills and valleys that cross the regular toolmarks at about
I have the same lathe (although 1950's vintage) and the same problem.  My
lathe was in like new almost unused condition when I bought it.  I have
tried adjusting everything to perfection but still get marks about 1 cm
apart when turning.  It doesn't seem to matter what feed I use the marks
still apear around 1 cm apart.  I am inclined to believe it is common to
this lathe and has something to do with the way the carriage follows the
bed ways.  Perhaps they ways are not finished correctly?

I have noticed that it is difficult to get good accuracy out of this
machine regardless of how well it is adjusted.  Have you had similar
problems?

John Nicol			[email-masked]

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From: "Randolph Lee" <[email-masked]>
Date: 19 Sep 96 11:49:41 -0500

>> diagonal hills and valleys that cross the regular toolmarks at about
John Nicol <[email-masked]> typed
>I have the same lathe (although 1950's vintage) and the same problem. 
>My lathe was in like new almost unused condition when I bought it.  I have
>still apear around 1 cm apart. 

I had this on my Atlas until i replaced the leadscrew/nuts... it was pure
leadscrew wear on my machine...  that took care of 90% of it.... the rest
was fixed by resetting the spindel preload... but I know of other cases
where it was a problem with the leadscrew safety cluch... sort of a slip
stick problem caused by alignment and wear problems...