More Questions About Tailstock Alignment

[Luminast]

could it be possible that the tailstock was not a mate to that particular serial number? I know on screw machines all the drill saddles are bored and stamped with a machine serial number.

Thanks, I'll check. All of these comments also cause me to doubt my measurement. I will re-check it with another method.

 

[janvanruth]

I recently embarked on a project to fine tune the alignment of my lathe in preparation for my most ambitious project to date, WRT to accuracy. Previously, I've only been working to "farmer-repair" accuracy levels. Now I want to turn some parts to real fine accuracy.

I have the headstock aligned now. That was a big job, but it's done, and its nearly perfect.

I've finished alignment of the tailstock. It's about as good as I can get it, with about .001" horizontal variation when I unclamp the tailstock, move it 18 or 20 inches on the ways, and bring it back, re-clamp, and re-measure. It comes back to within about .001" (horizontally) of the same spot each time relative to the spindle, and within about .001" of matching the headstock centerline.

I also find that the tailstock centerline is about 10 to 12 thousandths above the centerline of the spindle. I've read a couple of places that this is intentional on the part of the manufacturer to allow for future wear. Is that correct?

I can understand how that vertical alignment error is not of serious concern if our turning/cutting tool is set on center, but my real question is what this means for center drilling operations. If the tailstock center is 12 thou. above the spindle center, will every center drilled hole be 24 thousandths oversize? Or will a drill tend to 'hunt' and find the center of the piece? Will the geometry of the center drilled hole still be correct to fit the tailstock center?

Can someone explain? I expect that once you explain this, the answer will be obvious, but my mind is getting twisted around the geometric implications, and I don't know which way it goes, and I can't seem to find this answer in a prevous thread.

How did you measure the 12 thou?

 

[Luminast]

How did you measure the 12 thou?

I've now measured it two different ways. In preparation, I turned a pair of 4MT to 3JT adapters to remove the taper on the 3JT end, and make that end straight. They were turned carefully so that the straight section of both adapters are the same diameter. They are the same within about .0003". (This is the method that Tubalcain suggests in his Machine Shop Tips #96 video on Youtube).

For the first test, I installed one of those adapters in the tailstock, attached a dial indicator to the 4-jaw chuck, and rotated the spindle as I indicated the adapter held in the tailstock.

For the second test, I installed one of the turned adapters in the spindle, and one in the tailstock. I moved the tailstock towards the spindle to position the two adapters face to face just touching. Then, with micrometer, measure across the junction of the two adapters. The edges of the two adapters were offset about .001" on the horizontal, and offset about .010" on the vertical.

There is the third method, which I haven't yet completed. With one adaper in the spindle, and one in the tailstock, move the tailstock rearward, setup the dial indicator on the saddle, then indicate each adapter by moving the saddle.

Unfortunately, both methods indicate about the same vertical misalignment.

Thanks for asking. Do you see any mistakes that I might have made?

 

[12bolts]

Have you had the tailstock apart? Any chance you dislodged a shim, or got some crap in between the 2 pieces?

Cheers Phil

 

[Luminast]

Have you had the tailstock apart? Any chance you dislodged a shim, or got some crap in between the 2 pieces?

Cheers Phil

Yes, I had it apart earlier this week to free up the side to side adjustment. There were no shims, and the mating surfaces all looked good, but I may take it apart again just to look for anything that might be amiss that could be affecting the height.

 

[janvanruth]

I've now measured it two different ways. In preparation, I turned a pair of 4MT to 3JT adapters to remove the taper on the 3JT end, and make that end straight. They were turned carefully so that the straight section of both adapters are the same diameter. They are the same within about .0003". (This is the method that Tubalcain suggests in his Machine Shop Tips #96 video on Youtube).

For the first test, I installed one of those adapters in the tailstock, attached a dial indicator to the 4-jaw chuck, and rotated the spindle as I indicated the adapter held in the tailstock.

For the second test, I installed one of the turned adapters in the spindle, and one in the tailstock. I moved the tailstock towards the spindle to position the two adapters face to face just touching. Then, with micrometer, measure across the junction of the two adapters. The edges of the two adapters were offset about .001" on the horizontal, and offset about .010" on the vertical.

There is the third method, which I haven't yet completed. With one adaper in the spindle, and one in the tailstock, move the tailstock rearward, setup the dial indicator on the saddle, then indicate each adapter by moving the saddle.

Unfortunately, both methods indicate about the same vertical misalignment.

Thanks for asking. Do you see any mistakes that I might have made?

You did the measurements twice,first with the quil retracted and than with the quil extended?
You stated the centerline of the quill was parralel with the centerline of the spindle.
How did you measure that?

 

[Luminast]

You did the measurements twice,first with the quil retracted and than with the quil extended?
You stated the centerline of the quill was parralel with the centerline of the spindle.
How did you measure that?

The first measurements with dial indicator attached to the chuck was done with the quill retracted. The dial indicator setup just reached across the cross slide to the end of the adapter inserted in the tailstock quill.

The second measurement, measuring across the junction of the two adapters (one in the spindle, one in tailstock quill) that were face-to-face just touching, was with the quill extended to reach over the cross slide.

I did not mean to imply that I know that the centerline of the quill is parallel with the spindle. If I left that impression, then my words were not carefully chosen. I am sure that the spindle centerline is parallel to the bed because I set that very carefully myself. And I am sure that the end of the adapter inserted in the tailstock quill is on the horizontal centerline of the headstock spindle (within .001").

Only by inference, I might presume that the quill centerline is parallel to the centerline of the spindle because both the horizontal offset and the vertical offset indicate the about same with the quill retracted and with the quill extended. But I have not thought about that until you ask.

 

[JR49]

I have the headstock aligned now. That was a big job, but it's done, and its nearly perfect.

If the tailstock has no shims between the halves, and you 're sure it is the correct tailstock, then, is it possible that when you aligned the headstock, It somehow dropped down by .010 when you tightened everything down? Jr49
EDIT, Just realized this is an old post. I'm sure you got it figured by now. I sure would like to here what the fix was. Anybody Know?