Reply with QuoteDoes the out of round get worse as you get further from the headstock?
Out Of Round Lathe Parts
I have a lathe that consistently cut 6 tenths out of round, we just replaced the spindle bearings and the problem did not go away or get better. I suspect that the spindle tube is bent but I'm having a hard time convincing the boss. Can a bent spindle cause an out of round condition?
Similar Threads:
Does the out of round get worse as you get further from the headstock?
i replied to this in the other thread, but this new thread is a better idea - what does out of round mean? it's cutting an ellipse?? have you indicated the spindle and what were the results? have there been any crashes on the machine that you know of?
Why do I get the feeling that "defective bearings" just MAY have been uttered somewhere's after this problem reared its ugly head???
Did you measure for high point of eccentricity of spindles and/or bearings prior to R&R' them? Or did you just throw them on, sorry, merely install new bearings and bolt it back together???
If you just R&R'd the bearings, did you then grind the chuck mouting surface square in-place after replacing the bearings??? If not, WHY???? This is a mandatory part of a precision spindle rebuild if you want perfectly concentric/round cuts.
I echo the comments about "out of round" by Mcgyver. Many spindle problems are often misdiagnosed/misdescribed and out-of-round is one of them.
This very problem was discussed in a recent Bridgeport spindle bearing replacment thread that took place on the zone. Same church, different pew.
Find it, point you boss to it, and let him read for himself. If he still feels that the bearing replacement procedure may not be the true source of your woe's, there ain't much you can do about it - I strongly suspect that a improperly executed procedure is the source of your problems.
Sure would have been nice to check the spindle tube while you had it out of the machine.
However, if you have not yet touched the front face of the spindle, an indicator reading there should be dead steady.
What kind of turning are you doing? Chuck only or chuck and tailstock? Long parts?
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)
Yes it is cutting an ellipse, length from tailstock = more elipse, and it was just bolted back together with the new bearings. The goon that did the work took a die grinder and a stone to the chuck mounting seat of the spindle (I have no idea why!). After the "repair" I made a cut that measured six tenths out of round. When I placed an indicator on the cut I just made, the TIR was six tenths. An indicator on the bore of the spindle only runs out 1/4 tenth. It seems to me that if it were the spindle, then you would see the same six tenths in the rotation of the spindle. Can a chuck that is not mounted perfectly true cause an out of round condition to occur?
This is total speculation but the only way I can think of to get a lathe to cut an oval is to have some damage to the bearing seat on the spindle so that the inner race is distorted into an oval shape. Perhaps when the original bearings were installed something galled up so a high spot was created. Simply taking the original bearings off and replacing them with new bearings would just distort the replacement bearings in the same manner as the originals. I would take everything apart and check all the bearing seats on the spindle for concentricity.
Thats what I think! But try explaining that to a guy with too much experience to learn anything new!
Face to face I would be quite happy to do that; I completed my apprenticeship in 1964 and I don't accept that many people have more experience than me. But I sympathize with your situation having been faced with s****d o** ****s in the past.Originally Posted by chipslinger
No mention made so far as to why bearings were changed in the first place.
If you go back thru the "process" SOMETHING should become indicative (intuitively obvious is an oxymoron) as to what is contributing to the condition.
Like in "if something is high here it should cut LOW there" sort of thinking. Even the most obstinate, hard core doofus even starts to "see the light" after a while. Or they simply say "fix the G/D thing" at some point as opposed to admitting they don't know what's going on and that's as close as they can come to admitting the haven't a clue.
When I was visiting the machine tool bearing plant in Japan for machine tool bearing training, an interesting observation occurred: there were NO hammers and NO abrasive media of any kind in the bearing assembly areas. They wouldn't even let you mark the spindle with a magic marker!!! Didn't see any such primitive "repair" devices while at the Hardinge spindle shop either. Strange, isn't it???
Simply put, I'd be inclined to show the DOOR to any "service technician" who got near my spindle with a hammar or a grinder of ANY kind.
If you can't fix/dress it with Scotchbrite or paper towels either it ain't broken or it needs to be PRECISION REPAIRED (as in ground undersized, hard chromed and then reground RECISELY to size).
Are you measuring the 6 tenths out of round on the parts while they are still in the chuck without unclamping them? I see out of round or ovality in parts due to high clamping pressue and chucks distorting the parts. Check the part after cutting and before you unclamp the part.
Try this... Cut a part then stop. Indicate where the cutter cut the part with an indicator then indicate the other side of the part. If you have .0006" 180 degrees away from the cutting point and zero at the point of cutting, I would suspect a bent spindle. Or at least something pushing it around. Bad bearings would cause double runout and the .0006" would be 180 degrees from point of cut and the point of cut location would be more like .0003".
I would be tempted to disassemble and this time look at everything for straightness, squareness, roundness or any other ness you can think of. I might even look at the spindle housing for out of round condition and or misalignment of the front bearing mounting compaired to the rear bearing mount. Oops that aint a ness but you know what I mean.
Regards Walt..
PS NCCams, Some spindles need grinding, some don't. I don't think this spindle needed ground. Straightened more likely....
Same here
I have the same problem with an old lathe. It turns in oval shape. I had the suspection that the chaulk was the cause because the spindle bearings are in cone shape.
Did u find any solution to the problem?
Hi, one thing is for sure, if you've got ANY problems with ball or roller bearings, they aint gonna last, and if they're in a high precision machine they definately will not last. Old lathes with bronze bearings always ran smooth till one day they just couldn't be adjusted any more. All that changed with the onset of high speed steel and carbides.
If the person responsible for your machine maintenance wasn't up to it, how did he get the job in the first place? In the firm I last worked for we had Nakamura nc's and we always flew a guy in from Japan at a humunguous rate of dollars to fix any crash ups. You only get what you pay for, and a poor man always pays twice. Who's been saving money then?
Might I add to that speculation wherein the bearings/races may not be perpendicular to the centerline that contributes to this condition? A slight bend, burr, contamination or bolt torque distortion of the bearing seat areas could contribute to this. Chuck mounting surfaces won't. If the bearings spin the spindle true, whatever is turned in the chuck may have runout, but the cut would return true to the axis it is spun on.
How about improperly set bearing preload? Is the elipse shape consistant along the length of the cut or does is rotate?
DC
Now I'm curious, It would be difficult in my mind to cut a part oval in a lathe, but it would be easy to cut the center line off from what you expect or want. If you were cutting the part in precision bored soft collets, and using a trammed in t-stock and the part still measured oval then its time to tear the machine head stock down and find out why. is this oval being seen by a od mic or an indicator, a mic will not lie to you, but an indicator measuring an off center condition will look oval. More than likely a bent spindle, mest up face, or bad bearings would only show a pee poor finish, lots of out of place tool paths. I've cut parts on some old beat-up lathes and had some poor finishes i couldn't do anything with but sand them in, but they were round !
Don
IH v-3 early model owner
Hi all, it is the easiest thing in the world to cut a part that measures oval.
In addition to this it is also just as easy to cut a part that has a raised spiral pattern round it axially. Herein lies the clue. What parts actually touch the spindle of a lathe?
The answer will be given in ten minutes while I pop off to make a cup of hot chokkie.
Ian.
Hi, 20 years ago I rebuilt a 10" swing Colchester Bantam centre lathe from the ground up, recutting all the Vees and flat slides by hand.
Some time later while doing a job I noticed a raised pattern like a coarse spiral thread running round the job.
It appeared as if the spindle had gone slack in the bronze bearings , but this was not the case. After a number of cuts the pattern dissapeared and all was well.
Two days later while turning another job a new pattern appeared. This time it was a straight raised hump that went along the axis of the job. MOST peculiar Ollie.
Was this a "pattern maker's " lathe. No such luck. This last pattern got less and less and finally settled down to a small hump that ran along the job. I won't bore you with the hair tearing,teeth gnashing new swear word inventing that occured, but needless to say it peed me off a bit.
I would go as far to say that all centre lathes have a gear at the end of the spindle that mates with another gear and so on till it connects to the feed gearbox and leadscrew.
All have extra gears to allow for those odd threads not covered by the feed gearbox.
"Most" lathes have a cover at the end of the lathe that is swung out to gain access to the gear train. The lathe spindle sticks through the cover when it is closed and here the ghost is laid.
The reason it sticks through the cover is to allow swarf that migrates down the hollow spindle from drilling and boring to fall to the floor.
What had happened was, a chip of steel had wedged into a gear tooth bottom, the second one that meshed with the spindle gear and as it was the same number of teeth as the spindle gear, it always came round at the same place and exerted an upward pressure to the spindle.
The spindle, running in bronze bearings, just got a nudge each revolution, which was enough to make the tool mark the job in a most peculiar way.
The wavy pattern was caused by a similar occurance but in another gear of different ratio so causing a cyclic pattern.
Now this lathe is a veteran of some years, 1920 to be exact, and it doesn't have a cover for the gear train so all the bits of swarf fell into the gear train and that was it.
Solution, till I make a cover is to bung the spindle hole up with a wad of paper.
With this experiance fresh in my mind I would examine any lathe to see if the gearing or anything connected to the spindle was in any way influencing it.
Sometimes the gear train that connect to the leadscrew is meshed too tight and also causes a staggered pattern.
Ian.
Hi all,
Handwanker has valid point(me thinks).Am in process of replacing bearings in am M5 Yamazaki,the finish ,weather face, od, id or back face,was increasingly wavy(without tailstock). my first thought was head stock bearings,$$$$! during teardown ,bad input splineshaft & sheavecoupler,
no way to tighten,adjust,so(rebuild or new part)$$$$.so think thats the problem,but must clean everything while shaft is out.inspecting ,cleaning,find metal pieces that should not be i here! bearings in "hi" drive clutch pack are laying at the bottom of the race,(cage remaings from earlier ?) long story reaching end,a lot of bearings out or going out. Will make for strange finish patterns(unaccapetble(I wouldnt buy it)).
Bear
To cut an over, you need to REPETITIVELY inject a force so as to cut deeper in that same area.
A malfunctioning bearing tends to make a repetitive defect BUT at a much higher frequency than at a rate of once per rev as an oval part would require.
Depending if the bearing defect is a damaged ball (one or more) or raceway (inner or outer, single or multiple defects), you will first see a finish defect (chatter or the like0 which then gets worse and worse.
But a pure and simple oval. I"d contend that far too much coincidence would have to repetively occur for a bearing to create such a perfectly repetitive defect.
Wanker's suggestion of debris in a geartrain is a logical and viable explanation as any and more logical than a chuck defect or a bogus bearing. Sure would be a head scratcher until the "DUH, now I see it, it is clearly obvious" moment that we all have.
Posting Permissions
