How much spindle movement is normal

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atunguyd
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How much spindle movement is normal

Post by atunguyd »

Hi can I pick the brains of the more experienced guys here.

I have a Sieig SC8 lathe, which is essentialyl an 11x35. I am busy trying to fine tune it for better performance (not that I am battling with anything I just like to tinker and try to make things better). Some of you may have seen my post a few months ago on trying to level it with a plumb bob and a digital microsocpe.

Well anyway today I put a dial indicator onto a bar mounted in the chuck and I noticed that if I put pressure on the chuck by hand (either towards me or away from me) the dial indicator measures a movement of about 0.01mm (or 4 ten thousands). Pushing on the outboard side of the spindle I can reproduce the same thing in the same direction (ie if I push the outboard away from me the chuck also moves away from me by about 4 ten thousands).

My question for you guys is if this is normal or something that I should look at addressing (maybe new spindle bearings or pre-load the bearings more?).

I dont have anything to compare to and my previous lathe as a 7x10 (and I never thought to check this either).

Thanks in advance.
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Steggy
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Re: How much spindle movement is normal

Post by Steggy »

atunguyd wrote: Sat Jan 30, 2021 4:00 pm...Well anyway today I put a dial indicator onto a bar mounted in the chuck and I noticed that if I put pressure on the chuck by hand (either towards me or away from me) the dial indicator measures a movement of about 0.01mm (or 4 ten thousands)...My question for you guys is if this is normal or something that I should look at addressing (maybe new spindle bearings or pre-load the bearings more?.
If the lathe uses tapered roller bearings to support the spindle, there should be no radial or axial movement, as the bearings are run at zero clearance. There will be a means to adjust bearing preload, which should be done after running the lathe long enough for the bearings to reach normal operating temperature. You want a very slight amount of drag when you manually rotate the spindle. Too much preload will cause the bearings to overheat at higher spindle speeds and rapidly accelerate wear.

Tapered roller bearings generally have a long life if adequately lubricated. So it's unlikely they would need replacement, unless the lathe has not been maintained or has been crashed. In the latter case, a sudden shock to the spindle can cause spalling in the right-hand headstock bearing, which will cause the bearing to become sloppy and rough-running. The only cure for that is to replace the cone and cup as a unit. As doing so means disassembly of the headstock, it would make sense to replace both bearings, not just the bad one. Needless to say, the oil should be replaced and the headstock oil cavities thoroughly cleaned to get rid of any metallic junk that may have collected.

If the lathe uses plain bearings, some clearance will be necessary to allow lubricating oil to get into the space between the spindle journals and the mating bearings. Four tenths would be acceptable in this case.
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pete
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Re: How much spindle movement is normal

Post by pete »

As BDD mentioned if it's got tapered roller bearings they should be preloaded to just about a zero clearance condition. Spindle measurement in either up/down, towards/away from you is still only half the measurement as he again pointed out. It's axial float or back and forth within the bearings also needs checking. There's also a measurable difference between checking clearances with a cold machine and one that's been run for 1/2 - 1 hr to come up to it's usual operating temperature. You'd obviously want to measure what the machines bearing clearances are after that warm up period.
atunguyd
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Re: How much spindle movement is normal

Post by atunguyd »

Thanks for the feedback, so concensus seems to be that this movement is the bearings and not spindle flex (pity I thought I may be that strong). Apparently the lathe has a tapered bearing near the chuck and a normal bearing on the outboard side so I probably need to look at how that tapered bearing gets preloaded.

Lathe was bought new and has never bee crashed - I also do not use it a lot so I doubt there is wear on it, probably just the quality control on the manufacturer's side.

Here is an extract from the user manual
Screenshot 2021-01-31 115001.jpg
Screenshot 2021-01-31 115553.jpg
252 is the spindle locknut which I assume when tightening will pull the spindle more into the roller bearings and preload them.
Will play aroudn tonight.
pete
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Re: How much spindle movement is normal

Post by pete »

That's a fairly standard bearing arrangement for lathe spindles since it allows the spindle to lengthen or shorten as it's temperature changes. Better would be two opposed tapered bearings at the front for much better load bearing of course, but it will still work. I'd be careful how tight you adjust, run it at high speed after your adjustments for at least 1/2 an hr and check for extra heat with your hand. Too hot to keep your hand on or around the front bearing area is likely a bit too tight for that lathe.There's also shouldn't be any real excess drag on the spindle when you try quickly rotating the chuck by hand. Lot's of other forum posts around with a few tips if you run a Google search for Lathe Spindle Bearing Adjustment.
atunguyd
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Re: How much spindle movement is normal

Post by atunguyd »

Tried tightening on the "spindle locknut" but it was very tight and the only way I could tightening it further was to lock the chuck with a bar through it and add a pipe to the supplied spindle spanner for more leverage.
Didn't seem to make a difference.

Perhaps I need to strip it down first to see how it all goes together before I try force anything.

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Russ Hanscom
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Re: How much spindle movement is normal

Post by Russ Hanscom »

Is there a locking screw or tab for the spindle locknut, many are so equipped.
atunguyd
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Re: How much spindle movement is normal

Post by atunguyd »

The spindle nut has two locking screws for it (both I removed before trying to tighten the spindle nut.

Spindle nut is exactly like the one in the video (totally different lathe though). You can see it at the one minute mark in the video
https://youtu.be/a3oB256L1wA

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Glenn Brooks
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Re: How much spindle movement is norma

Post by Glenn Brooks »

Iam not familiar with your model lathe, so may be completely out of line here, But,,, isn’t 4 tenths basically nothing to worry about? Unless you are doing high end aerospace work, do you really need to hold that level of precision? I am wondering if your measured runout may be within the manufacturer’s specification?

I mention this as many, (most?) of the plain bearing lathes here in the US allow up to .001” to .002” preload. Now your bearing and spindle design sounds like a higher quality machine. So maybe talking to the manufacturer might resolve whether it’s worth dissembling or not...

I’d be very curious to hear what you discover.

Cheers,
Glenn
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atunguyd
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Re: How much spindle movement is normal

Post by atunguyd »

So after pulling the entire spindle out (almost) I realised that the spindle nut does preload the taper bearing but it actually presses against that circlip in the diagram (via the radial bearing). Also that bearing is a press fit onto the spindle so it needed a fair amount of banging with a dead blow hammer to move the spindle relative to it.
This makes me believe that any adjustment puts an axial force on that bearing which I do not think it is designed to to handle.

Would probably not be so bad if the bearing was not such a tight fit on the spindle.
By tightening the nut with an abnormal amount of torque (ie used a 2 foot pipe on the spanner) I was able to preload the roller bearing enough that the deflection when I press on it halved, however after running the lathe with no load for 20 minute's the spindle was quite warm making me think I am creating premature wear.

I put it back how it was and left it at that.
As I said there is no problem (one strange thing but I will start another topic about that) so perhaps 4 ten thousandths is OK.
If I want to try this again I may start by buying new bearings.

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Bill Shields
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Re: How much spindle movement is normal

Post by Bill Shields »

I do not own a lathe that has such a small amount of 'axial float'.

I would not worry about it, and leave well enough alone...you can well make things too tight and overheat / overload the bearings if you are not careful.
Too many things going on to bother listing them.
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