Tailstock Alignment Puzzle - HELP

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Phil3

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I have been trying to make sure the tailstock is aligned on my 1946 Southbend 9A. Really puzzled here and maybe someone can point out what I might be doing wrong.

I mounted a magnetic base with dial indicator to a faceplate and then rotated it around the inside of the tailstock spindle, the outside, an inserted dead center, and an arbor/drill chuck assembly. One hopes the indicator will not move during this exercise. I was not that lucky, but you would think that any difference in readings (side to side, up and down) would be the same no matter what I measured off of Not the case. I can adjust side to side to be perfect using the spindle and then measure against the dead center, and the total side to side differential may be .010". I can not conclusively know whether the side to side adjustment is right, since it depends on what you measure. Same thing for vertical, but incredibly, the tailstock spindle (or dead center or drill chuck w/bit) all measure HIGH. Typically about .009"! Maybe someone shimmed the tailstock (far too much), or given the other results on side to side, maybe I just can't measure properly, or something is wrong with my indicator setup.

I installed a dead center in the head stock and another in the tailstock. I put them nose to nose. They are as dead on as I can see. I pinched a metal rule between the two to see if the ruler deflected from the points being off center. No deflection at all. How can this be if my measurements show at least a .009" vertical misalignment? I can not see why the measurements would be wrong. The tailstock and its spindle are both locked down during measurement. I rotated the indicator without it touching anything to make sure gravity is not affecting it. It appears solid.

I am exasperated. Suggestions welcomed!

Thanks.

- Phil
 
I just put dead centers in each set it side to side and if its low I use Shim Stock. If-n I did what your doing I throw it out the door.

Have you turned a part to check alignment? If it is Larger on the tail stock end move the tail stocl towards you. If it is smaller move it the other way. This is the only way I do it and it works for me!

Paul
 
Might just be indicator sag. If it is worn, it will be low, not high.
 
Phil3 said:
I have been trying to make sure the tailstock is aligned on my 1946 Southbend 9A. Really puzzled here and maybe someone can point out what I might be doing wrong.

I mounted a magnetic base with dial indicator to a faceplate and then rotated it around the inside of the tailstock spindle, the outside, an inserted dead center, and an arbor/drill chuck assembly. One hopes the indicator will not move during this exercise. I was not that lucky, but you would think that any difference in readings (side to side, up and down) would be the same no matter what I measured off of Not the case. I can adjust side to side to be perfect using the spindle and then measure against the dead center, and the total side to side differential may be .010". I can not conclusively know whether the side to side adjustment is right, since it depends on what you measure. Same thing for vertical, but incredibly, the tailstock spindle (or dead center or drill chuck w/bit) all measure HIGH. Typically about .009"! Maybe someone shimmed the tailstock (far too much), or given the other results on side to side, maybe I just can't measure properly, or something is wrong with my indicator setup.

I installed a dead center in the head stock and another in the tailstock. I put them nose to nose. They are as dead on as I can see. I pinched a metal rule between the two to see if the ruler deflected from the points being off center. No deflection at all. How can this be if my measurements show at least a .009" vertical misalignment? I can not see why the measurements would be wrong. The tailstock and its spindle are both locked down during measurement. I rotated the indicator without it touching anything to make sure gravity is not affecting it. It appears solid.

I am exasperated. Suggestions welcomed!

Thanks.

- Phil
Click to expand...

Can you lose the magnetic base and chuck up a DTI using a dovetail to shank adapter and indiocate the tailstock spindle bore? I used to set-up that way until I got a coaxial indicator that can go into my homemade collet closer. Enlightening to say the least. That method showed how easy it is to get junk under the tailstock.

John
 
I did put a dead center in the tailstock and one in the headstock and they look lined up perfectly. I pinched a steel ruler between the two and the ruler stayed staight, no matter how I oriented it. I then put a 9" long piece of aluminum bar that is about .690" in diameter. Only about .375 in diameter for about 2.5" at one end. I put the bar between centers with the small diameter end at the tailstock. I made a very light cut and then went over it again twice at the same cutting depth to eliminate as much possible bowing of the work piece. This was evident, as additional passes took more metal off in the middle of the piece than at the chuck end. After two additional passes, very little metal was coming off. Mostly fuzz. I measured the diameter of the bar about 1.25" from the tip of the dead center in the chuck and then about 3.5" out from that, or just about mid way on the bar. I was shocked. After repeated measurements, which were always very close to being the same, the difference in diameter between both points on the bar is about .0003". Not .003, but .0003". I need to do this again with a solid piece of steel to validate my findings. But, if those readings are true, then my measuring with the dial indicator leaves much to be desired, although I do not know why. I am especially amazed because the tailstock spindle has some noticeable slop in it.

- Phil
 
Sounds like it's aligned pretty well, Phil. I don't think I would try to adjust it after that test. Most turning tests use a dumb-bell shape, with a relief in the middle so that tool wear won't be a factor. Turn one, then without moving the cross slide move over and cut the other. Measure the difference.
 
Is it possible that the outside diameter of the dead center is out of round or out of center. I wouldn't assume that the outside of the dead center is true. Your other tests sound more conclusive. Seems like you've got a good setup.

If you want to check the dead center, place a mark on it with a felt pen, at the top when mounted in the TS. Run your indicator test. Then remount it with the mark turned 90*. Repeat the indicator test. Do this at all four quadrants. If it's out of true, you will see four very different results.
 
Hi Phil,
I would say your high reading was from indicator sag and gravity, as it will give you a high reading doing it that way.
The best way I think is to machine a piece of steel or aluminum in your chuck the same diameter as you tailstock quill and leave it their. Then bring the tailstock quill up to it and run the indicator on top of one onto the other. This way eliminates any sag or gravity errors.

As for aligning it side ways perfectly, just make up a bar with 2 collars on it what ever length you want (say 300-400mm long) after setting you tailstock as true as you can, grip one end with the chuck out 10mm and the other end onto a live/dead centre. You then machine the tailstock end collar and without touching any dials move the carriage along and take a cut off the headstock end collar. Measure both collars and adjust the tailstock as necessary, then repeat the test until they are both the same size.
It can also be done between centres using a lathe dog, but it's less mucking around and quicker using the chuck.

To save time and waist, you can weld, press fit, etc the 2 collars onto a piece of bar. I would recommend around a 20mm bar and the collars around 30-50mm round. This should last you many times of setting the tailstock exactly over the years to come.

Some guys have the different length 2 collar test bars on hand so they can use them to set up the tailstock perfectly the different length jobs. If the tailstock is set up with a test bar and not moved, it will make the job turn out spot on.

There are many different ideas and ways to set up a tailstock, but I think this is one of the more accurate ones. It is called the 2 collar test and if you Google it you will see a lot of references to it.

Dave
 
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