Replacing TOS lathe spindle bearings
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  1. #1
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    I'm involved in a job where I have to replace the spindle bearings in a TOS SN40-C engine lathe. I have worked on many lathes before but this one is a strange beast. The headstock is a two piece afair with the backend being the transmission and the front end housing the spindle. From the looks of the parts manual it looks as if there is a splined or keyed connection between the transmission and the spindle.
    I called TOS and the parts guy said that you unbolt the transmission and slide the headstock forward on the ways. From my examination of the assembly, it looks as if I have to remove the gearbox to get at the bolts holding the back of the spindle housing to the bed. That gearbox looks heavy and there is no provision for lifting bolts. This looks to be a major PITA.
    The spindle bearing set up is strange as well. On the front of the spindle is a double row roller bearing (not a Timkin tapered bearing, straight rollers here) designed to take the radial load and at the rear end of the spindle is a duplex bearing to take the axial load. I would imagine that the duplex bearings are factory preloaded and need no further adjustment. The front bearing sits on a taper and the bearings have a matching taper in the ID as well. There is a shim spacer between the bearing and the shoulder on the spindle. Giant hug nuts hold this all together. I'm thinking I may have to mess with this shim to set the radial play to some nominal amount, like maybe 0.0002 or so. Kind of like on a Deckel milling spindle.
    Has anybody done this before? Any tricks or short cuts to help out here? I love it when a manufactor comes up with a "better idea" and makes it so darn complex. I have quite a few TOS lathes in my service area and have worked on a few but never in the headstock. Thanks in advance.
    Bill

  2. #2
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    Mr B,
    Gimme a couple of hours - part way thru a job and I'll dig the book out.
    They are a bit weird, had one to bits a long while ago for bearings.
    Note you have to use the right oil, it's like piss, or it takes the bearings out.
    The SN I have at the moment is about 15 years old and never had a spanner on it yet, built like a brick shithouse and it's on it's third chuck.

    John S.

  3. #3
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    T.O.S. lathes are EXREMELY common in Canada, as well as their model 25 turret mill. When the iron curtain was still up, America didn't allow the import of them so they were incredibly cheap in Canada, and like John says they are really heavy duty machines.

  4. #4
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    You might try Omnitrade in Toronto lots of those machines up here so their service dpartment should have someone that can help. If you need the number let me know
    Bob

  5. #5
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    The taper bore anti friction bearing was an SKF idea. They were originally used with a bushing that had a tapered OD and an ID that fit a common line shaft. The bushing is split and the inner race of the bearing and the shaft OD are brought tight with each other by turning the "SKF Nut" on the small end of the bushing.

    Then someone got the idea of making SKF bearings, both spherical roller and straight roller types in precision grades and jamming the tapered bore on a solid shaft so that the inner race swells up and removes the radial clearance.

    This is tricky at best.

    In many applications there is a spacer used on the side of big end of the bearing's taper bore that fits against the shaft shoulder. This spacer's thickness is unique to the bearing that is installed. It gives the proper pre load when the bore is jammed full tight.

    One big problem is getting the taper bore bearing off from the shaft or spindle.

    Look for a 1/8" NPT pipe plug on or near the face of the spindle. This covers an oil hole that leads to the OD of the tapered part of the spindle that is within the inner race.

    Remove the plug and use a high pressure pump (porta-power) to force oil into that passage. The oil "pops" off the inner race. Hint: don't unscrew the SKF nut all the way off the threads.

    When going to assembly, expand the bearing on it's taper outside of the machine first and check the pre load. I can't give a figure, but the pre load is not great. There should not be any radial clearance.

    Sometimes there is a "stand off" dimension etched on the new bearing. This is the thickness of the spacer required to achieve the proper pe load when the taper bore is jammed tight.

  6. #6
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    Hi all,

    Does anyone know how I can align the headstok of a tos sn50?

    My lathe has a difference of 0.05 mm, and I want to align the machine.

    Has anyone done this?


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