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Thread: Worn bearings

  1. #1
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    Default Worn bearings

    Hi all,

    I have noticed that my 9" Hercus displays a little tiny bit of play in the head stock such that when turning steel bars of only 5cm length, there is up to 0.10mm difference between the tailstock end of the turned bar and the head stock end which is up to 0.10mm narrower, when not supported by a dead center in the tailstock. THe steel bar is 13mm thick and at 5cmm projecting from the chuck, it doesn't seem that the bar itself is flexing but rather the whole kit n kaboodle is being forced out a tad by the force of the cutting tool, causing the far end to be turned at a slightly greater diameter than the chuck end of the bar. If I patiently do a number of very light cuts and subsequent sweeps of the tool, I can eventually get a parallel cut.

    I have tried aligning the bed thinking that perhaps there was some twist but still no difference.

    In an endeavour to eliminate play in the head stock I have removed some shim from the head stock spindle bit and tightened the screws to just before the point where the spindle binds. But still there is enough play for the turned stell not to turn parallel.

    Does it sound like a replacement bearing is necessary? If so, where do I get replacement bearings from, and how much?

    Cheers.

    Davidg

  2. #2
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    If your lathe is a Roller Bearing model not a problem you will be able to get a useable replacement.

    If it is a standard Spindle you will find that the spindle is just running in the Head Stock.

    If after you do your checks to see how much clearance you have between Spindle and Head Stock,your choices are a bit limited.

    If the Headstock is worn you could Line Bore the Head Stock bearing area and then fit Bronze Sleeves then rebore to suit spindle.

    If the Spindle is worn you could machine damaged area and shrink a sleeve on then get it ground back to diameter.

    Another allternative to sleeving the spindle would be to get it either hard chromed or metal sprayed and then machined to correct diameter.

    The last choices you have are to get a replacement Spindle,Head Stock or both.

  3. #3
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    Thanks Pipeclay. Without actually pulling it apart, is possible to tell if it is a roller-bearing or not? Here's a couple of pics attached or at this link -





    Cheers...

    '

  4. #4
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    Ausdag,
    The photo shows a plain bearing headstock.
    The side play of the bearings I have been told is .001". Measure this with gauge and a heavy rod slid into the spindle to give a bit of leverage.
    Can I ask: What oil are you using for the bearings, is there wear on the bed ways, do you get chattering with a heavy cut?
    The spindle is straight forward to strip down, a bit more tricky to assemble. But this will show if the wear is very bad.
    Generally the plain bearing headstocks last a very long time, and a second hand one would be the way to go if this one is very worn.
    Peter

  5. #5
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    Hi Peter,

    I've had the lathe only about 6 months and until find a better lubricant I have been using SAE 30 / API SF Monograde 4 stroke engine oil.

    I'm unsure about wear on the bed - I used to get a bit of chatter until I tightened up the carriage and cross-feed and chatter is no longer an issue.
    I'm not sure just how much side movement there is - I don't yet have a gauge to measure it - but I can feel and even see that sometimes as I move my tool off the tail-stock end of an unsupported piece of steel bar (as in my initial post) after making a heavy cut, the whole thing 'pops' back to centre after having been forced towards the back by the cutting tool. This is what seems to be causing the non-parallel finish.

    Quote Originally Posted by brittleheart View Post
    Generally the plain bearing headstocks last a very long time, and a second hand one would be the way to go if this one is very worn.
    Peter
    So I should try and replace the entire headstock, not just the spindle? If I wanted to replace the headstock or just spindle, where would be the best place to get one from?

    Thanks for your help.

    Cheers,

    DavidG

  6. #6
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    David,
    The oil you are using is too heavy, try an ISO 32 hydraulic grade oil. This equates to roughly a 15 SAE engine oil and doesn't have other nasty additives in it. OK, it might not be the absolute perfect type. But for our purposes, it is adequate.
    With the lighter oil, try tightening both front and rear bearings till it is tight to turn by hand. Now back the bolts off slightly till they are free.
    With a bit of trial and error, you should be able to get a good clearance. If there is considerable wear, the tolerance (or wobble) will be greater in the horizontal plane rather than the vertical plane.
    You can get a cheap indicator to check the differences.
    IF this is obvious, then consider getting another headstock.
    My suspicions lead to a loose saddle, check that the rear plate is a snug fit.
    Regards,
    Peter

  7. #7
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    Quote Originally Posted by brittleheart View Post
    David,
    The oil you are using is too heavy, try an ISO 32 hydraulic grade oil. This equates to roughly a 15 SAE engine oil and doesn't have other nasty additives in it. OK, it might not be the absolute perfect type. But for our purposes, it is adequate.
    With the lighter oil, try tightening both front and rear bearings till it is tight to turn by hand. Now back the bolts off slightly till they are free.
    With a bit of trial and error, you should be able to get a good clearance. If there is considerable wear, the tolerance (or wobble) will be greater in the horizontal plane rather than the vertical plane.
    You can get a cheap indicator to check the differences.
    IF this is obvious, then consider getting another headstock.
    My suspicions lead to a loose saddle, check that the rear plate is a snug fit.
    Regards,
    Peter
    Thanks Peter. Where can I purchase hydraulic grade oil from? I don't think I've seen it at the local bunnings or supercheap.

    The saddle I'm fairly certain is as tight as I can get it without it becoming too hard to move and I pretty certain that the wobble is in the headstock but I'll have another inspection.

    I've not seen replacement headstocks. I imagine it would be a matter of scouring the online auctions?

    Cheers,

    DavidG

  8. #8
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    For the oil try an oil supplier,I my self use a 46 hyd oil for all parts of the lathe.(you can also try construction machinery dealers or spare parts suppliers for 4 litre bottles)

    When you come to do your checks for clearance mount your dial indicator as close to vertical centre of your spindle.

    If you have the chuck on place suitable stock in the chuck and lift,see what movement you get,you can also push down but normally you want get much if any movement as the spindle would have bottomed out on the spindle bore.

    If you like you can do the same test on the chuck end of your spindle by placing a piece of hardwood under your chuck or spindle and levering it up,(there is no need to put a bar in the chuck if you wish not to do this test(if you do use a bar it will have to be one that dosent flex to much.

    With the change gear end you can do the same test with the indicator vertical but this time unless you remove the reverse gears and other gears in the train you may not be able to get anything under the spindle to act as a lever,(in this case put a piece of 3/4" bar about 300mm long into the rear of the spindle by about 75/100mm and lift up and take your reading.

    In regards to the previous post if you tighten the bolts down on the bearing cap you will have to remove the shims,if not I doubt that you will see any noticeable change unless there was allready clearance between the bearing cap and shims.

    In regards to Horizontal wear in your spindle use the steel bar and push and pull ,if you see wear or movement that way it is not good,you probably wouldnt even need the indicator to show it,you should be able to see and hear it.

    I think you mentioned that when you machine with the use of a centre in the tailstock that you parallel problem is not present.

    From my understanding if there was horizontal play in your spindle the problem would still be there.

    The material you are using is only 1/2" this in its self could be flexing even though you only have 50mm out of the chuck,is it possable to try a larger diameter piece of stock say 1"to 2" and see if the problem persists.

    If it is still no good pull the spindle apart and measure to see where the wear is in the Headstock and also on the spindle,before thinking of replacements.
    Last edited by pipeclay; 27th Jan 2010 at 01:08 AM. Reason: More Info

  9. #9
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    Thanks Peter and Pipeclay for the valuable advice. I'll start with locating a more suitable oil then have another go at the shim in the bearing cap and inspect the saddle. A gauge will be my next purchase so I'll try and nut it out and see what I find.

    Thanks again,

    DavidG

  10. #10
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    For the oil, try Pirtek - they deal in hydraulic hoses and equipment and will have the hydraulic oils.

  11. #11
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    I think with a total loss system, engine oil would be as good as any, it may be slipperier then hydraulic oil...

  12. #12
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    I think the subject of "what oil is the best" has been dealt with on numerous threads.
    The most suitable viscosity, is the grade that has been allowed for in the design of the bearing itself. Given a certain design clearance, this determines the viscosity with respect with expected rotational speed. The prime objective it to have a layer of oil between the bearing faces.
    Slow rotating plain bearings with large clearance = high viscocity oils. (gear shafts)
    High rotating plain bearings with close clearance = low viscocity oils. (headstock)
    This makes sense as the headstock needs to be accurate.
    Given that there will be some wear in these older machines, a heavier viscosity could be used, providing no adjustment to tighten the bearing is made.(If this is done, it's back to normal clearance).
    With the spindle bearings on my milling machine, which are preloaded and capable of high speed, I have to use a very low viscosity oil (about 15 ISO). Not easily obtainable, so I use a pneumatic gun lubricating oil.
    The most annoying thing about oil grades, is the number of different viscosity descriptions there are.
    See this table to get confused.
    Peter

  13. #13
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    Looking at the table, another option for light oil might be bike fork oil?

    fork oil chart

    cheers

    Kevin

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