Possible spindle problems on a Sharp 2280 lathe..? (20,000+ hours on machine) [cutting tapers into the face of plates].

[Bill Good]

I was recently using a 30-year-old Sharp 2280 lathe on a chuck adapter plate project at work. The other day I made a couple of large adapter plates on the machine which wound up having a .003" - .004" taper across the face of the plate. My usual machine was being serviced. The plates were finished on a fixture which typically eliminates the possibility of this type of taper. (The fixture is an aluminum plate that is cut fresh each time before mounting the adapter plate to it that is to be finished, the adapter plate is then bolted to the fixture and finished ensuring flatness & parallelism). I've done this plenty of times on a different machine without an issue, but for some reason on this machine both plates I finished are not parallel and have a taper across the face.

Any ideas? I know the lathe probable has 20,000+ hours on it and is 30 years old...

My thought is that it might be the spindle bearings.

 

[Finegrain]

I don't see how bad spindle bearings causes this.

Headstock badly misaligned?
Crossfeed ways all jacked up?

 

[ClappedOutBport]

I don't see how bad spindle bearings causes this.

Headstock badly misaligned?
Crossfeed ways all jacked up?

Agreed. If Bill can set a boring bar or some other tool to be able to cut on the backside of the part and the taper flips, I would say the headstock is out of alignment. With full length cross-slides, I would be surprised at that level of damage.

 

[Bill Good]

I don't see how bad spindle bearings causes this.

Headstock badly misaligned?
Crossfeed ways all jacked up?

I remember being told by a HAAS tech during a class (years ago) that a badly worn spindle bearing can have the effect of rotating with the face out of alignment, particularly with an unbalanced load, which will pull towards the heavy side when rotating due to the combination of axial and radial run out caused by a worn bearing or other badly worn part...)

 

[Bill Good]

I remember being told by a HAAS tech during a class (years ago) that a badly worn spindle bearing can have the effect of rotating with the face out of alignment, particularly with an unbalanced load, which will pull towards the heavy side when rotating due to the combination of axial and radial run out caused by a worn bearing or other badly worn part...)

Rotating with the spindle out of alignment and pinned to one side due to balance would have the effect of cutting a taper across the face. I'm curious if anyone has ever seen the same thing, and if so, what was the age of the machine.

 

[swarfless]

'Taper across the face' pretty ambiguous. Which was? convex or concave? If concave it could be well within spec of the lathe. You don't tell us the OD of the part either .. so 0.003/4" in how many inches ? Nor do you say if the fixture machined in situ is similarly 'tapered'. If the part is convex it could indicate wear in the cross-slide.

 

[farmersamm]

Instead of all the speculation............put an indicator on it(shrug)

Do a facing cut to load the cross slide, and watch what the indicator is doing.

 

[Limy Sami]

Back to basics, are you locking the carriage for the facing cuts

 

[Booze Daily]

SFM changes drastically across a large face. Could be the insert is cutting poorly towards center and gets better as diameter increases.

 

[Doozer]

If you have bad spindle bearings, you will hear it
and cuts will always chatter, unless you use tailstock
center support. Probably not bearings if it is only a
geometry problem.

-Doozer

 

[Dan from Oakland]

Seems a quick OD pass on a piece of bar stock held in a chuck would tell a lot about how much the headstock is out of alignment if any. As a start anyway................