Subject: Lathe roller bearing adjustment

From: [email-masked] (Richard W. Klopp)
Date: 1 May 1996 20:37:31 GMT

The bearings on my 12" Jet lathe heat up a lot with continuous use on the
higher speeds. The spindle is also stiff to start turning after sitting. I
have a hunch that the previous owner set the bearings too tight when he
installed a Royal lever collet closer attachment. Can someone tell me the
proper way to adjust the bearings? Do I go for a certain preload (measured
how?), a certain starting torque, or a certain fraction of a turn of the
nut after finger tight? I'm worried that if I keep running as is, I will
toast something.

-- 
Rich Klopp
[email-masked]

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From: [email-masked] (Jonathan M. Elson)
Date: 3 May 1996 19:10:26 GMT

Richard W. Klopp ([email-masked]) wrote:
: The bearings on my 12" Jet lathe heat up a lot with continuous use on the
: higher speeds. The spindle is also stiff to start turning after sitting. I
: have a hunch that the previous owner set the bearings too tight when he
: installed a Royal lever collet closer attachment. Can someone tell me the
: proper way to adjust the bearings? Do I go for a certain preload (measured
: how?), a certain starting torque, or a certain fraction of a turn of the
: nut after finger tight? I'm worried that if I keep running as is, I will
: toast something.

FIRST, what are you lubricating the bearings with?  Precision machine tool
spindle bearings are usually lubricated with a light oil.  My Atlas 10"
specifies SAE #10 oil.  My Bridgeport specifies something obscure, but I
think it is a similar weight.  If you are using grease, that is definitely
your problem!

On my Atlas, the preload procedure calls for heating the spindle by running
at a medium-high speed (sounds like 1000 RPM, maybe) for a half hour.  You
might have to loosen the bearing preload first.  This expands the spindle,
reducing preload on this arrangement.  Then, tighten the preload nut until
'slight drag' is felt.  (Ah, now that's a precision measurement.)  Then
tighten the preload nut two gear teeth further.  (on this lathe, the preload
nut is right next to the gear that drives the leadscrew gears.)

Now, that preload setting is obviously specific to that particular lathe,
but you get the general idea.

I still have a strong suspicion there is grease packing in your bearings!

				Jon