# Tailstock Alignment



## P.K. (Mar 31, 2015)

Hi all

Is this a good way to align the tailstock?
I'm going to test for taper as soon as I can get my hands on some suitable aluminum round stock.


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## seasicksteve (Mar 31, 2015)

Sure that will work. You could read directly off the inside of the tailstock quill as well, it would eliminate adding another variable. Many time the tailstock will be a little high but you can still center it up side to side. Dial it in and make some test cuts as you planned


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## atunguyd (Mar 31, 2015)

Not sure about doing it that way. Your three jaw is not going to be aligned with the bore of your lathe so you will just align the tail stock with the three jaws axis not your lathes axis.


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## P.K. (Mar 31, 2015)

atunguyd said:


> Not sure about doing it that way. Your three jaw is not going to be aligned with the bore of your lathe so you will just align the tail stock with the three jaws axis not your lathes axis.



Yea, I guess you're right, but at least it will be a good starting point after having had the tailstock apart.


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## RJSakowski (Mar 31, 2015)

It does not matter if the chuck jaws are concentric  with the spindle axis.  The indicator is off center anyway.  As the chuck (and indicator) rotate, the contact point will follow an arc concentric with the spindle axis.  Any non uniform deflection caused by the tailstock center  not being aligned with the  spindle axis will be indicated as runout.  The only downside that I can see is the difficulty in reading the indicator when the dial is facing down or to the back.  An inspection mirror should solve that one.


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## kd4gij (Mar 31, 2015)

I aagree with most of what rj said. But the op is using a coaxial indicator. the dial stays put and the insides move.


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## geryuri2 (Apr 1, 2015)

This is not the best way to align a tailstock.  At best, you are extending the headstock spindle axis to the end of you dial indicator.  So if your headstock is (angularly) off a bit, this will magnify that error.  You could dial this in "dead" and still turn tapered parts between centers.  Turning straight parts using the tailstock center, and drilling are the two main times you want your tailstock aligned.
  The best ways are: ground parallel test bar with accurate centers and dial from tool post between centers; or better, turn a test piece and mic for parallel.  The ability to turn a perfectly parallel test piece is more difficult than you might guess, because the amount the tailstock is off doubles on the diameter of the work piece.  If your tailstock is off .0005" then the taper is .001"  Even if you have your tailstock alignment close, you will discover that where the tailstock is on the bed plays a role, depending on how accurate your bed is.
Gerald


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## randyc (Apr 2, 2015)

Gerald is right but if your resources are limited (and the lathe ways are relatively unworn) your setup might be the best one for you.  Don't use the live center as a reference, sweep the tailstock *taper* with your DTI.  Probably want to run the tailstock ram out about half-way and lock it when you do this.


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## 18w (Apr 2, 2015)

Two things, Dial indicators and the coax indicator are affected by gravity. When a dti is held in a horizontal position  and you sweep your tailstock the top and side readings will be correct. The reading on the bottom can be several tenths off do to gravity pulling on the probe. Richard King always suggested chucking up a piece and turning to the exact dia. of your tail stock spindle.Do not support it with a center, just turn about a 6" long area.  You then put your dti on the top of the turned piece and then move the saddle towards the tailstock and traverse the top of the tailstock and do the same on the side. This give you your readings for height, side to side and parallelism of the tailstock. This is of course, after assuring that your lathe bed and headstock are aligned first. The above posters are correct though in that your coax may get you close enough. Depends on your requirements. 

Darrell


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## chips&more (Apr 9, 2015)

18w said:


> Two things, Dial indicators and the coax indicator are affected by gravity. When a dti is held in a horizontal position  and you sweep your tailstock the top and side readings will be correct. The reading on the bottom can be several tenths off do to gravity pulling on the probe. Richard King always suggested chucking up a piece and turning to the exact dia. of your tail stock spindle.Do not support it with a center, just turn about a 6" long area.  You then put your dti on the top of the turned piece and then move the saddle towards the tailstock and traverse the top of the tailstock and do the same on the side. This give you your readings for height, side to side and parallelism of the tailstock. This is of course, after assuring that your lathe bed and headstock are aligned first. The above posters are correct though in that your coax may get you close enough. Depends on your requirements.
> 
> Darrell


Sorry, but no I don’t think so, at least not my test indicators. Yes, gravity can effect an indicator if you drop it on the floor! But to have the reading change because gravity pulls on the stylus/probe??? If there was any change in the reading, then IMHO it’s probably due to lack in rigidity somewhere  in the total indicator set-up and not gravity pulling on the stylus. However, when using a test indicator you can get readings that are not quantitative. 1) Using the stylus at an angle other than from its true origin (straight out) will cause cosine error in the readings. 2) Using a stylus with a different length other than the calibrated length. If you are using the test indicator just for comparison readings, as in this authors example, then the above 2 concerns do not apply. And the top and bottom readings do not apply as well…Good Luck, Dave.


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## 18w (Apr 9, 2015)

chips&more said:


> Sorry, but no I don’t think so, at least not my test indicators. Yes, gravity can effect an indicator if you drop it on the floor! But to have the reading change because gravity pulls on the stylus/probe??? If there was any change in the reading, then IMHO it’s probably due to lack in rigidity somewhere  in the total indicator set-up and not gravity pulling on the stylus. However, when using a test indicator you can get readings that are not quantitative. 1) Using the stylus at an angle other than from its true origin (straight out) will cause cosine error in the readings. 2) Using a stylus with a different length other than the calibrated length. If you are using the test indicator just for comparison readings, as in this authors example, then the above 2 concerns do not apply. And the top and bottom readings do not apply as well…Good Luck, Dave.



I stand by my original statement however poorly described. Gravity indeed is pulling pressure away from the stylus or probe. I should have said gravity can affect the reading on the indicator because gravity has a effect on the indicator holder and indicator, which however small, can cause a sag which effects the indicated reading.   This is a separate issue from cosine error.  http://www.practicalmachinist.com/vb/general/headstock-bed-tailstock-alignment-257375/index2.html  Thanks for pointing out my poorly worded description.

Darrell


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## randyc (Apr 9, 2015)

I presumed Darrell's initial statement to be set-up related (Dave pointed out the same thing).  Nice to get a clarification, however.

Regarding the link that Darrell posted:  I'm a Richard King and Forrest Addy fan.  When those two guys make the same/similar statements, I'm inclined to treat it as carved in stone, LOL.


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## stupoty (Apr 9, 2015)

To get an initial rough alignment i use a dead centre in both ends and a mandril with centre holes.

Stuart


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## Dawner (Apr 9, 2015)

18w said:


> Two things, Dial indicators and the coax indicator are affected by gravity. When a dti is held in a horizontal position  and you sweep your tailstock the top and side readings will be correct. The reading on the bottom can be several tenths off do to gravity pulling on the probe. Richard King always suggested chucking up a piece and turning to the exact dia. of your tail stock spindle.Do not support it with a center, just turn about a 6" long area.  You then put your dti on the top of the turned piece and then move the saddle towards the tailstock and traverse the top of the tailstock and do the same on the side. This give you your readings for height, side to side and parallelism of the tailstock. This is of course, after assuring that your lathe bed and headstock are aligned first. The above posters are correct though in that your coax may get you close enough. Depends on your requirements.
> 
> Darrell


I disagree with every thing you said... except for your last statement   "Depends on your requirements"  However if your working for NASA or lives depend on it and your getting payed large sums of dollars to do it ... I totally agree with everything you said plus ten.  ( its a hobby )  Just saying Dawner


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## randyc (Apr 10, 2015)

Ha-ha, that's a good one, Dawner


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