To all,

Finally got the lathe in the shop and started tuning it yesterday.

Everything seems to be adjusting good. After I leveled the machine and made a test bar, I used it to dial in the tail stock with the headstock. This went very well as the tailstock quickly came into roughly 0.00015" horizontal alignment with the headstock. Plenty close enough for gunsmithing.

I next measured the height of the tailstock compared to the headstock and found it to be 0.005" higher then the headstock.

What effect will this difference have on accuracy?

Luckily, all I will need to do is mill off the proper amount to bring them into alignment but my mill is in the shop but not quite tooled up yet.

Will this 0.005" variation in tailstock elevation prevent me from putting out quality work until I get my mill up an running to correct the problem?

Your experience would be great!!

Thank you for your time!

Good Shooting!!!

50

Tell me how you determined that your tailstock was .005 higher than the headstock. I might be able to offer some advice, (been there, done that).

Rancher,

I cut a test bar by taking an 18" length of 4140 and faced and center drilled both ends. Then with the bar between centers I turned one end for 1.5 inches to a diameter of .950" just to make sure of the concentricity of the surface.

I then mounted a dial indicator compound rest and with the bar between centers and the turned end at the headstock, I preloaded the dial indicator and zeroed the dial. The measurement was taken at 12 o'clock.

Then the bar was reversed and installed between centers again with the turned section at the tail stock. The dial indicator rod was lifted off the bar and I traversed the carriage to the tail stock and lowered the dial indicator to the turned section and got a reading 0.005" higher then was given at the head stock.

To confirm this, I rezeroed the indicator and reversed the bar again. THe measurement was the same, the headstock was 0.005" lower then the tail stock.

The lathe is a Jet GH-1440ZX.

Hope this was enough information.

Thanks for your time!!!

50

I've been told that it's fairly common for the tailstock to be a bit higher.. But I don't care for that and took measures to correct it. The way I determined that my t/s was higher was to mount a test indicator on the spindle nose with a magnetic holder. Then I postitioned the t/s about where it would be during chamber reaming since that was the operation I was most concerned about. Put your indicator inside the t/s quill and bring it to bear. Then turn your spindle by hand and take notice of indicator movement. If your t/s is indeed .005 high remember to mill only .0025 off the base of the t/s.. If you take the whole .005 your will then be .005 LOW. A word from the wise!
However, if you do go to far you can get shim stock and bring the t/s back to .000 .. Ah, the lessons we learn..

This is not at all uncommon. It seems like new machines are frequently a bit high. Will it cause a problem? Not a great deal of error in turning a shaft for instance but it could cause a problem if you are trying to drill or ream something held in the headstock with the tool centered on the tailstock.
Perhaps an easier way to check co-axial alignment of head and tailstock is to mount an indicator on the chuck and simply sweep the tailstock center. This way you are checking only this alignment and not introducing any possible error which might exist in the ways.
The cure is to disassemble the tailstock, clean it up well and reassemble and retest. At the same time check to see that the tailstock quill is parallel to the axis of the machine. If the tailstock is still high then it can be scraped a to lower it's height. If the quill runs uphill, again the tailstock has to be cut down to realign it.
On one old worn lathe, on which the tailstock sat way low, I drilled and tapped the top part of the tailstock at each corner and installed setscrews which would allow me to adjust the height and attitude of the tailstock housing in relation to the base of the tailstock..
As I said, the amount of error you describe would have little effect when turning between centers (as in turning a shaft for instance)so it would be possible to thread a barrel that way if you wished and you would have no problems. If you wished to chamber in the heads stock you must use a method of holding the reamer which does not hold the reamer to the tailstock center axis. Otherwise you might be better of to chamber in the steady since then you can set the barrel at the same height as the tailstock center. With use your tailstock will wear down to a lower position while your headstock will not change so the problem may be self correcting over time.
It is often a good idea to turn a test piece in the chuck just to check that the headstock is properly aligned with the ways. It is not impossible that the headstock is not level with the axis of the ways or is misaligned laterally. To do this simply chuck a piece of easy turning material ( I like cast iron since it is relatively inert and machines well with light cuts) about 2-2 1/2 inches in diameter and let it extend about 5 or 6 inches. This should be rigid enough that deflection won't be a real problem. Turn it and measure for taper. If it is tapered, move the headstock to align it and recheck. You have to be quite fussy when measuring this. I figure .0002 of error in 6 inches is acceptable. Once you have achieved this you can mount a dial on the carriage and indicate the bottom of the testpiece and determine whether or not the headstock is level with the ways. Or you can set your precision level on the test piece and compare it with the ways.
In the end, some machines are perfect but it is probably rare. We got a 70,000 dollar Cinncinati CNC lathe in the shop with the tailstock .006" high as delivered so it can happen to anyone! One thing's for sure, after you've check everything out you will certainly know your lathe better! Regards, Bill.

I just worked on my lathe two weeks ago for having a tailstock ~.015" lower than the headstock.

One problem is the the left side of the tailstock is lower than the right side. So I extend the ram of the tailstock and measure the heigth with a dial indicator on a ponit on a took in the ram. That way I can calculate how much tilt the tailstock has.

I then took the tailstock appart and shimed the left side more than the right side and put it back on the lathe to see if centers matched and the ram extended horizonally. It took some iteration and when I cut the steel shims, I got a burr. When I ground off the burr, the shims turned into knife blades sticking out of the tailstock.

[image]http://www.benchrest.com/forums/attachment.php?s=&postid=34702 [/image]

Fiftydriver

First off let it be understood that I'm no machinist. Usually when I put something in a mill or lathe I brake it.(the part not the machine).
But shouldn't a floating reamer holder more than make up for your .005 deviation?

God Bless and Good Luck
Shawn

Thank you for all the information, gives a starting machinist new view points which are invaluable to say the least.

The first step I will do to correct this problem is to remove the tailstock and clean it totally. Then relube and remeasure.

If that does not fix the problem or at least get it very close, I will take 1/2 the difference off the head stock or perhaps 1/2 minus 0.0005 to 0.001" to allow some wear before shiming starts to be a problem.

Again thanks for all the experience you have had with your machines, it all helps greatly!!

Good Shooting!!!

50

In speakingwith one of our machinery suppliers today I heard an explanation for the common high tailstock. He claimed the tailstock were deliberately set high so that as the headstock warmed up from operation they would equalize. This may be a salesman's tale but it made as much sense as anything else! I'm going to let one of the lathes run for a half hour then recheck just to see what change there is. Regards, Bill.

Fifty:
What Bill said.
The tail stock is high at cold temps intentionally. Let it warm up and re inspect. The mass of material in the head stock determines the amount of variation. I would venture to guess that after your new machine is warm you will find the tail to be still .001 to .002 high. THe tail will wear in fast that amount after you use it for a couple hundred hours.

Alan