Out Of Round Lathe Parts

[chipslinger]

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?

[fyffe555]

Does the out of round get worse as you get further from the headstock?

[Mcgyver]

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?

[NC Cams]

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.

[HuFlungDung]

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?

[chipslinger]

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?

[Geof]

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.

[chipslinger]

Thats what I think! But try explaining that to a guy with too much experience to learn anything new!

[Geof]

Originally Posted by chipslinger 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.

[NC Cams]

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).

[Factory Guy]

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.

[Walt@SGS.Inc]

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....