eccentric headstock spindle

Any help please guys, this is driving me nuts !!
I have a Sphere centre lathe - basically an Atlas 10" with the Timken
roller bearings headstock option.
It was previously owned by a time-served engineer, sadly now passed away so I can't ask him, who I'm sure would not have tolerated an inaccurate lathe - so I must have done something.
The nosepiece mandrel on the headstock is apparently running eccentric. My DTI shows a range of 0.16mm from high to low point, at about 80mm in front of the front headstock bearing.
This eccentricity is consistent whether I fit a centre into the MT3 socket, or a faceplate or a 3 jaw chuck to the 1 1/2" x 8tpi nose thread.
I can fit and centre an independant 4 jaw to give very little drift (less than 0.02mm) - not enough patience to obtain zero, but I think it would be achievable.
Unless the spindle is distorted, I cannot work out how this could be happening and how to correct it.
I have recently replaced the belt which entailed removing the spindle from the headstock, all appeared to go by the book :-/ so hopefully that wasn't the cause.
Am considering stripping down the headstock, anybody with any experience? Why does book suggest driving spindle out through bearings rather than unbolting the tops from the split housing blocks?
Any help greatfully received
Dave
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Dave
Atlas lathes either had white metal headstock bearings with split bearing caps, or they had taper roller bearings with solid housings for the bearings which meant the taper roller bearing mandrel have to be driven out. I don't know if Sphere lathes are the same format.
Your description sounds as though the original owner converted your lathe to a taper roller headstock. It sounds as though the bearings are not adjusted properly so there is play. If you look in an Atlas lathe manual there is a section on adjusting headstock bearings.
If you haven't looked before check out Tony Griffiths' site http://www.lathes.co.uk/atlas/.
John H
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Hi John,
I have just looked at the lathes.co.uk site and it seems that the Sphere model might have been made in the UK and designed as standard to carry Timken bearings in a split housing - thank you for the link, it was most interesting and is now firmly bookmarked :-)
I have checked for play in the bearings but cannot detect, the Atlas manual suggests tightening until no play is evident and then adding 1/16 of a turn more, perhaps I need to be a little more brave?
Probably more sensible would be to strip down the headstock shaft assembly and check for problems, do you have any opinion to offer re taking the bearing caps off?
Thanks again Dave
wrote:

Dave
Atlas lathes either had white metal headstock bearings with split bearing caps, or they had taper roller bearings with solid housings for the bearings which meant the taper roller bearing mandrel have to be driven out. I don't know if Sphere lathes are the same format.
Your description sounds as though the original owner converted your lathe to a taper roller headstock. It sounds as though the bearings are not adjusted properly so there is play. If you look in an Atlas lathe manual there is a section on adjusting headstock bearings.
If you haven't looked before check out Tony Griffiths' site http://www.lathes.co.uk/atlas/.
John H
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Dave, you seem to have miseed the essential point about John's reply, which is that either your lathe has white metal bearings with split bearing caps, or it has roller bearings (as you told us) and no caps. So what have you got?
Cliff Coggin.
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I have Timken taper roller bearings with split bearing blocks, as per the Sphere section in lathes.co.uk - Sphere made the adaptation as standard to the original Atlas 10F design. Reading through the Atlas section, lathes.co.uk highlights that the Timken bearings had marks to show the "highspot" so that fine adjustment of the front/rear bearing alignment was possible, unfortunately these marks (if they were present) have worn off. I am wondering if the original alignment of these "highspots" is what I've upset when removing the spindle to change the drive belt? Additionally, checking the spec for the rear cone/cup bearing from Timken, the ID of the cone is 1.25" - the seating area on the headstock shaft is discoloured (brownish) and 1.2485" - 1.249" diam; could that be enough to cause me a problem? The front bearing as a tight fit to the shaft (requires bearing puller to remove) - should the rear bearing be the same?
Thanks again for everyones comments/suggestions
Dave

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Hi I am fascinated by this, I wonder if both the bearings are fully seating in their outers as play in one might cause this, yes you could have a bent shaft but you would know what you had done to cause that. I would have a look to make sure that the outers are properly seated and then ensure that the inners are also in the right position, remember the odd thou in play on the rear one was there before you dismantled things. Without seeing the assembly I asume that the thrust is taken by the front bearing and the rear inner is loose on the shaft and tensioned from the rear by a collar, the proper tension for this is quite tight and the bearings should be warm after 15minutes of running, is suspect that you may not have all the parts spotless and not enough tension. Peter
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Hi Peter,
that's a very good point that I'd overlooked in a rush to explain my problem - indeed the wear in the rear bearing would have been there already.
I shall carry out a scrupulous clean and reassemble.
Your description of the assembly is absolutely right, I'm not sure whether I've noticed any warmth from the bearings so I'll give that a check once I've reassembled - I guess by warm you mean comfortably touchable but noticeably warmer?
Thank you for your help
Dave
wrote:

Hi I am fascinated by this, I wonder if both the bearings are fully seating in their outers as play in one might cause this, yes you could have a bent shaft but you would know what you had done to cause that. I would have a look to make sure that the outers are properly seated and then ensure that the inners are also in the right position, remember the odd thou in play on the rear one was there before you dismantled things. Without seeing the assembly I asume that the thrust is taken by the front bearing and the rear inner is loose on the shaft and tensioned from the rear by a collar, the proper tension for this is quite tight and the bearings should be warm after 15minutes of running, is suspect that you may not have all the parts spotless and not enough tension. Peter
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Hi Dave
I've just looked at the Sphere section of the Tony Griffiths' site and have seen the photos of the headstock and mandrel assembly.
I would suggest that you pull the assembly apart, clean everything and put the caps back on the headstock with only the bearing outers in place. In this way you will be able to check if the races are being held tightly by the caps. The inner race has to be able to slide on the mandrel so that the adjustment can be made. If you think it is too slack assemble it with Loctite or similar 'bearing fit', the same remedy applying to the outer races if they are slack.
Taper roller bearings on Volkswagen wheel hubs are assembled only just pinched up, taper rollers on Velocette crankshafts have a fair amount of preload. As Atlas suggest pulling the bearing up tight and then giving the nut another 1/16 turn I would assume that the mandrel is more like the crankshaft
What I would do is assemble the clean headstock, pull the bearing up tight and then apply the extra 1/16 turn. To give a bit of leverage put a chuck or faceplate on the mandrel and see if it turns OK by hand. If not slacken the nut off a fraction and try again.
Let us know how you get on.
John H
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bromide wrote:

I had a similar problem once, and found that the main shaft was bent. No idea how it happened, it was straight before and then it wasn't.
I don't know the Sphere, but to adjust the taper roller bearings on my minilathe I tighten them up until they begin to bind, then slacken them off a bit, then tighten back to just before where they started to bind.
They don't get hot, at all, and the TIR under load is no more than a micron. I'm a bit suspicious of people saying bearings should get hot ..
The rear bearing "wear" - is it wear? I'm not clear on that point - sounds like it ought to be fixed even if it's not the cause of your present problem. Which it might well be.
What's the TIR at maybe 160mm from the front bearing?
-- Peter Fairbrother

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Peter Fairbrother wrote:

So would I be, but they didn't. Warm is the norm, hot is not.
--
Charles Lamont

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Dave, The various comments are valid, but even if the bearing outer is not properly seated it would not lead to an eccentric TIR. The spindle would be sloping, up, down or sideways, but not eccentric.
My father has a Halifax, so I am reasonably familiar with the machine. The rear bearing does sound rather loose. The brown deposit could be either dried grease or, much worse, the result of fretting to the shaft due to movement between the shaft and bearing. Probably the former, but either way a clearance will obvoiusly allow the spindle to adopt an indeterminate position which could lead to some misalignment. However, that would be half the clearance at worst so roughly 3/4 thou. This is not enough to account for the 6 thou TIR you measured especially bearing in mind that you measured 3" out from the bearing and the two bearings are probably 7" apart. The 'law of the lever' applies so for that source of the error, you would need more like 12 thou clearance in the bearing which is well into 'dick in a bucket' territory.
I would expect the reference to the 'high spot' of the bearing would adjust maybe a few tenths at most, as far as I am aware, the bearings are not deliberately eccentric to allow adjustment. If I were you, I would start by stripping the spindle again as others have suggested.
While it is stripped apart, try to arrange some centres and check the spindle for a bend. It seems improbable, but is would be a first thing to discount.
Richard
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Sorry guys, have been away for a couple of days and only just caught up with all your helpfull inputs. I stripped the spindle and set it up in my mates Harrison to check for run-out, couldn't detect any so reassembled and refitted after a good clean. Run out is now about 2 thou - an improvement anyway and one that I'll probably live with for a few months until I get more time - otherwise the lathe will hang around in pieces for ages :-( Did try rotating rear bearing seating to 4 different positions but no noticeable effect. May consider buying new bearing sets for the hell of it when I come back for another go.
Thanks again to everybody that has contributed.
Best reagards Dave
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