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spindle run out

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Ian MILLARD28/09/2010 22:21:27
18 forum posts
HI I have just measured the run out on my raglan five lathe. With a dti on the machined shoulder where the chuck locates there is a difference of 2 thou as the spindle rotates, the end of the spindle is about 3 thou. Is this normal or do i have a problem. Thanks  IAN
John Olsen29/09/2010 02:34:28
1223 forum posts
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1 articles
Sounds a bit much to me. Is the spindle itself out of true, or do the bearings need adjusting? If it is the bearings you will be able to change the reading by pulling the spindle back and forth or up and down. I just found recently that I had to adjust my ML7, and that was at least part of why I had started having trouble with parting off. Mind you, I think that might have been the first time since it left the factory some time around 1953 or so.
 
regards
John
KWIL29/09/2010 09:32:15
3477 forum posts
66 photos
Quoting Tubal Cain from ME 4 Oct 1996 Centre Lathe Inspection Limits
 
Chuck Seating Register  Schlesinger Limit  true TIR for 3.5" Model Engineer's lathe Allowance 0.0005" ACTUAL 0.00005"
 
I think you have a problem to solve.
Dinosaur Engineer29/09/2010 16:51:25
147 forum posts
4 photos
It would be difficult to do accurate work with spindle run-out this large .
Jeff Dayman29/09/2010 22:06:01
2199 forum posts
45 photos
As John Olsen said above - the spindle bearing clearance should be checked here first. .002 to .003" spindle runout is a lot, but if the bearing clearance is OK, even a running - out chuck will be able to turn good accurate parts as new work if the job is done in one setup and not removed and re-chucked. Work between centres will also be possible but the cut diameters will not be concentric to the centre drilling. If the spindle is bent, mounting drills or other tools in the spindle will result in a flailing drill / tool and ovesize holes (if the drill stays in the spindle at all.)
 
Check the spindle bearing clearance, then address the runout later. If everything else on the lathe including bearings is OK, it might be worth making or buying a new straight spindle.
 
good luck JD
Andrew Johnston29/09/2010 22:40:11
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6405 forum posts
682 photos
My gut feel is that 2 thou runout is quite a lot. If I understand it correctly from www.lathes.co.uk the Raglan 'Five' has taper roller bearings. Just out of interest I've been out in the workshop to measure the runout on my lathe nose spindle. It's a D1-4 fitting, and the spindle runs in opposed taper roller bearings.
 
Measurements were made using a Mitutoyo 0.01mm DTI. Measurements are:
 
Inner MT5 taper: 0.005mm
 
Short Outer Camlock Taper: 0.007mm
 
Outer Diameter (plays no part in locating the chucks): 0.01mm
 
Front Face of Spindle: 0.01mm
 
These measurements are from a 30 year old lathe.
 
However, before we panic and start stripping the spindle it might be worthwhile discussing the measurement technique, so as to be sure that the runout you are seeing is genuine. For instance did the needle move smoothly as the spindle was rotated, or did it move in jumps? If the needle jumped is there any corrosion or pitting on the spindle. Were the readings repeatable from one rotation to the next?
 
Regards,
 
Andrew
John Olsen29/09/2010 23:15:27
1223 forum posts
92 photos
1 articles
Since I had just adjusted my ML7 recently, I just put the indicator on it to see what I can see. (couldn't remember what my checks at the time said, except it had about 4 thou of play in the front bearing beforehand.)  With the indicator reading off the register, I see a total indicator runout when I rotate the lathe by pulling on the motor belt of less than 0.005 mm. That is interpolating, since the devisions on the dial are 0.01 each and would be about 1and a half mm wide on the dial.
When I put a shaft into the taper and pull, I can get about 0.02mm of total movement either up and down or front and back. But these are plain white metal bearings and there has to be some clearance for oil. When I adjusted it I took one too many shims off and it was too tight to turn. So I think I have it about right now, it is certainly parting better than it was for a bit there.
 
The dead centre could be trued in place. It would then have to be marked so it can be replaced in the same position. If the chuck backing plates were turned with the spindle off centre they will work OK too. (If they are the type with backing plates.) But I would not care to work like that...if the spindle is actually bent I would want to get it sorted. The more accurately you can work, the easier the later operations down the track are.
 
regards
John
 
 
Nicholas Farr30/09/2010 10:14:14
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3148 forum posts
1434 photos
Hi Andrew, when you say your tapered roller bearings are opposed, I assume that there are two single row bearings at each end of the spindle in a back to back arrangement which is normal for a headstock. Back to back arrangement is when the cups of the bearings are towards each other, whereas a face to face arrangement is when the cones are towards each other. The differance will be the adjustment needed. With the back to back arrangement there will be zero or negative clearance (axial preload) as opposed to face to face arrangement there will be a positive clearance. Having a positive clearance in the lathe spindle which results into end float is not desirable in our lathe spindle. I'm sure you understand this, I've posted this for those who do not realise the differance.
Regards Nick.
Ian MILLARD30/09/2010 17:43:27
18 forum posts
Thanks for the info. I hadnt tightened the spindle bearings up enough, with these tightened further and a centre in the spindle taper the runout is below a thou, however when i fit the faceplate and run the lathe the whole lathe rocks back and forth is this just because the faceplate needs a balance weight attached.
Andrew Johnston30/09/2010 19:51:18
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6405 forum posts
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Ian,
 
Definitely doesn't sound right. The faceplate, by itself, should be reasonably well balanced, certainly up to hundreds of  rpm. What speed were you running at?
 
Nick,
 
Yes, didn't explain myself very well. My lathe spindle has two 'Super Precision' Gamat bearings, one at each end of the spindle. It's not clear from the manual, but I presume that the bearings are arranged such that, as the spindle warms up and expands, the axial load on the bearings increases. The manual has a section on how to test the torque necessary to turn the spindle once it is warm, and how to adjust the preload in small steps. It also contains dire warnings about doing so, with strict instructions to contact the factory beforehand. Unless I have an unforeseen problem I have no intention of touching the bearings.
 
Regards,
 
Andrew
Ian MILLARD30/09/2010 20:08:45
18 forum posts
Andrew
I am running the lathe at its slowest speed in normal range ie not back gear. ian
Nicholas Farr30/09/2010 21:48:18
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3148 forum posts
1434 photos
Hi Andrew, it is little long winded to expland but, in a good design the preload will remand the same at whatever temperature the headstock is, within the makers specs for duty cycles ect. as the radial and thermal expansions cancel each other out when in back to back arrangement. It's all to do with choosing the right bearings for given loads and distance between bearings ect. ect. If one is not familar with adjusting taper bearings it is best to heed makers warnings, because too much or too little preload will shorten bearing life as well as too much lubricant.
Regards Nick.
Andrew Johnston30/09/2010 23:10:56
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6405 forum posts
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Ian,
 
That definitely isn't right. I assume that low speed without backgear is about 150-200rpm. At those sorts of speeds the faceplate must be wildly out of balance to be rocking the lathe. Or there is another, as yet undetected, fault with the spindle. Does the lathe do the same with a normal 3 or 4 jaw chuck, or just the faceplate?
 
Nick,
 
Thanks for the information. I hadn't thought about the axial and radial expansions cancelling out. The headstock itself gets mildy warm (about 30°C) after a few hours of running at 1200rpm plus. So I assume that tends to counter the expansion of the spindle too. I've made the assumption that the Harrison design engineers knew what they were doing and I'm going to leave well alone. I have never had any issues with accuracy or vibration that could be attributed to the spindle, so no need to fiddle. Not the real engineers' way I know, but I believe that if it ain't bust don't bugger about with it!
 
Regards,
 
Andrew
Nicholas Farr30/09/2010 23:36:59
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3148 forum posts
1434 photos
Hi Andrew, believe me, but in industry even some "real engineers" have the same policy especially if routine maintenace cost a lot ££'s or needs a lot of down time.
Regards Nick.
Ian MILLARD01/10/2010 13:42:30
18 forum posts
Andrew
I think i have a dud faceplate that came with the lathe. the centre fixing hole is a couple of mm off centre, its no problem the whole thing was bucking about. Thanks for the help  IAN
KWIL01/10/2010 15:08:42
3477 forum posts
66 photos
Super Gamet bearings on the Harrison.
 
Sorry Nick, you have it the wrong way around. Back to Back is where the outer raceway Cups are facing outwards with the inner raceway Cones facing inwards, so tha axial preload works inwards. Check SKF website if you disagree.  That is the arrangement on the Harrison which of course are not SKF bearings!!
Nicholas Farr01/10/2010 16:00:08
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3148 forum posts
1434 photos
Hi Kwil, I havn't got it wrong, We are saying the same thing, it's our termanolegy that is different, mine was probaly not clear enough. When I said towards each other, I mean the other bearings elements are not inbetween. Here is a simple sketch to clarify what I mean for back to back arrangements, more commanly found in lathe headstocks than face to face.

 
Regards Nick.

Edited By Nicholas Farr on 01/10/2010 16:30:17

Andrew Johnston03/10/2010 09:55:43
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6405 forum posts
682 photos
Nick,
 
Thanks for the sketch. That's just how I imagined the bearings in my lathe would be orientated. It always amazes me that the lathe spindle and bearings are subjected to all sorts of cutting forces, yet retain an accuracy measured in tenths.
 
Regards,
 
Andrew
KWIL03/10/2010 10:11:20
3477 forum posts
66 photos
Nick,
 
We are in agreement!   Good quick sketch for the uninitiated. I used SKF terminology.
ady03/10/2010 10:17:22
612 forum posts
50 photos
If you can run the faceplate at low speed and it fits the spindle nose well you can skim it until it runs true.

Some faceplates have a "middle bit"(spindle adaptor) and are not a single one piece casting, if this is the case the middle bit probbly needs adjusting.
 
Suss it out before you start any cutting.

Edited By ady on 03/10/2010 10:18:32

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