# Tailstock Setover Adjustment (was Alignment)



## cdhknives (Jul 6, 2013)

I just reviewed the machined bar alignment test and realize I forgot to relieve the center...but tell me if this looks like a reasonable measurement?  Should I go cut the center and re-machine the ends to recheck?


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## Ray C (Jul 6, 2013)

*Re: Alignment*

You're 3 thou off end-to-end which is pretty good...  There's a little problem though...  You're holding with a jawed chuck and supporting with the TS.  Under normal circumstances, you'd want to move your TS 1.5 thou away from you.  The problem is, the shaft is being held firmly by the jaws.  You could try to loosen the jaws a bit to allow the shaft to move a little but, I can all but guarantee, you're going to chase your tail as things will settle into different positions each time.   If you don't loosen the jaws and try to strong-arm the TS over by 1.5 thou, a thin bar like that will bend (ever so slightly) as it rotates and you'll end-up with an inverted barrel profile.  As is, what you're kinda doing, is a TS alignment test.  To do that "by the book" you should spin between centers.

To do the 2-collar test (which is what I think you're after), you'll want to use a piece of stock at least 1-2" diameter -preferrably aluminum -and you'll want to relieve the center.  Also, don't support the end in the TS.  Take an extremely light cut as not to put a lot of force on the shaft.

Make sense?


Ray




cdhknives said:


> I just reviewed the machined bar alignment test and realize I forgot to relieve the center...but tell me if this looks like a reasonable measurement?  Should I go cut the center and re-machine the ends to recheck?
> 
> View attachment 56690


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## Richard King (Jul 6, 2013)

*Re: Alignment*



cdhknives said:


> I just reviewed the machined bar alignment test and realize I forgot to relieve the center...but tell me if this looks like a reasonable measurement?  Should I go cut the center and re-machine the ends to recheck?
> 
> View attachment 56690



I tell folks to relieve the middle when checking the head-stock alignment with the bed. You could undercut the test bar you have but I would leave it the way you would be using it when cutting a shaft.  It looks like the tail-stock needs to be adjusted over .0015 as it is now closer to the tool bit.  I would mount a mag base on the bed with the shaft as straight or even with the center point as you can, mount the indicator on the bar and zero it  Then loosen the tail-stock nut, but keep it snug and adjust the TS over, re-tighten the nut and see what the indicator reads.  When you have it as close to .0015, take another cut.  When the ends read the same measure the bar every inch or so and see what the readings are.  This will show you if the bed is worn if the size changes.  I am assuming you have the quill locked during the cuts, right?


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## Ray C (Jul 7, 2013)

*Re: Alignment*

BTW:  If you're not familiar with the term "spin between centers", it mean you use a point at both the chuck and tailstock end and you drive the shaft with a "dog" which is an object that bolts to the end of the shaft and has a protrusion which comes in contact with a faceplate that is driven by the spindle.  It's possible to mount a pointy piece in the jaws of a normal chuck and drive the protrusion off the face of the chuck.  This is a little kludgy as it can scratch-up your chuck.  Enclosed is a picture of a type of "dog" that I make which is very non-traditional but, it has an advantage of being somewhat balanced (unlike normal dogs) and is universally adjustable for different diameter shafts (unlike normal dogs).  What's being shown is a MT3 center installed in the spindle and my special dog is bolted to a face plate.  The dog also has adjustable beams that close-in on the shaft and some bolts in those beams transmit rotation to the shaft.  Feel free to make one of your own...  The idea was self produced but, it falls into the category of "intuitively obvious" and is at best worth a design patent -and I don't even bother with those.

Also, if you leave your setup alone and strong-arm the TS by 1.5 thou and if it cuts straight, it probably means your spindle bearings are wiggly and taking-up the slack.






EDIT:  Here's a picture of a very traditional lathe dog being driven off a chuck face.  I don't like doing this since it beats-up the chuck...  (Picture taken from google images)


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## Richard King (Jul 7, 2013)

*Re: Alignment*

There are several ways to skin a cat as you can see many have different methods we have been taught and are trying to teach you  You need to find the method that fits you and fits your tooling.   I have turned several shafts using the loosening the tailstock as the bed is or was so worn I had to do it that way  This is why I suggested you mic the shaft in several places.  You will get push away in the middle, that is why you need to take a last clean up cut of .001".  From the looks of your shaft you had a good finish.  The last time I saw a machinist use a lathe dog on a lathe was 40 years ago in a high school.  I see them in grinding shops used more on cylindrical grinders between centers.


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## Bill Gruby (Jul 7, 2013)

*Re: Alignment*

I use the lathe dog many times. I also use the steady rest in conjunction with a cat head to keep the  hold during offset  turning crank journals. It's SOP and the easiest way to offset. This does take us a little OT, just saying that the lathe dog is used quite a bit in my shop. But then again this is as you say turning between centers, not what you are trying to accomplish here.  Just pointing out that some use them on regularly.

 "Billy G"


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## Ray C (Jul 7, 2013)

*Re: Alignment*

Bill, do you use the traditional style dogs?  I bought a set long time ago and found they are not balanced and things vibrate like crazy beyond a certain RPM.  Are there commercial ones that don't have that problem?

I'm thinking about selling the ones I have but am torn about it.  I can't bring myself to pawn-off stuff I don't like in exchange for money.


Ray




Bill Gruby said:


> I use the lathe dog many times. I also use the steady rest in conjunction with a cat head to keep the  hold during offset  turning crank journals. It's SOP and the easiest way to offset. This does take us a little OT, just saying that the lathe dog is used quite a bit in my shop. But then again this is as you say turning between centers, not what you are trying to accomplish here.  Just pointing out that some use them on regularly.
> 
> "Billy G"


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## Bill Gruby (Jul 7, 2013)

*Re: Alignment*

Yes Ray. I also have some others that I made.

 "Billy G"


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## cdhknives (Jul 7, 2013)

*Re: Alignment*

Okay, how do I tell if it is a up/down (wear) or left/right (can adjust) alignment issue?


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## itsme_Bernie (Jul 7, 2013)

*Re: Alignment*



Ray C said:


> Bill, do you use the traditional style dogs?  I bought a set long time ago and found they are not balanced and things vibrate like crazy beyond a certain RPM.  Are there commercial ones that don't have that problem?
> 
> I'm thinking about selling the ones I have but am torn about it.  I can't bring myself to pawn-off stuff I don't like in exchange for money.
> 
> ...



I use them too- but always the smallest I can use on a particular project.  But I haven't really used them at very high speed.  

I got a hood of some ridiculous size ones someplace, that won't even TURN on my 10L!  Hah hah- still thinking (for a little while longer) that I might find some use for them before selling them for the mere $5 I could probably get.

Bernie


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## Kroll (Jul 7, 2013)

*Re: Alignment*

I don't know if this will help any but trying to access,for me sometimes I can read it and still not get it,so I will read it several times when someone gives and answer to one of my questions.Either before or after I will search Youtube to see what I can find,sometimes it helps me to word my questions better.So here is what tubelcain has to say http://www.youtube.com/watch?v=WLXL3cdnbpM
-----I love this place---kroll


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## Ray C (Jul 7, 2013)

*Re: Alignment*

The TS has a bigger diameter than the HS end.  This means the TS end did not get cut as much as the HS end therefore, you need to move the TS end toward you now.  That will move the work closer to the bit to take off more material.  Obviously, the goal is to position the piece so that you don't get a taper.   Subtract the two diameters and divide the result by two.  That's how far you must move the TS toward you.  In this case 0.002".  BTW, it's not easy to make those tiny adjustments.  You will need to chase this back/forth a few times.

What this is really doing, is aligning your TS.  Theoretically, once aligned, it should be aligned at all distances from the chuck but, this is most often not the case.

FYI:  I'm building a new TS for my lathe; the reasons of which are many but one, is to include a fine adjustment of this sort.



Ray



cdhknives said:


> Okay, how do I tell if it is a up/down (wear) or left/right (can adjust) alignment issue?
> 
> View attachment 56733


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## Ray C (Jul 7, 2013)

*Re: Alignment*

Oh, I can't see in the picture how you're holding the piece... still using a jawed chuck or turning w/a dog?  How we proceed and what we can learn from the results are different depending on how the work is held.

Ray


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## Ray C (Jul 7, 2013)

*Re: Alignment*

Easy answer on this one my friend...  Just keep those ridiculously large dogs as encouragement/desire to one day get a lathe big enough to use them.


Ray



itsme_Bernie said:


> I use them too- but always the smallest I can use on a particular project.  But I haven't really used them at very high speed.
> 
> I got a hood of some ridiculous size ones someplace, that won't even TURN on my 10L!  Hah hah- still thinking (for a little while longer) that I might find some use for them before selling them for the mere $5 I could probably get.
> 
> Bernie


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## itsme_Bernie (Jul 7, 2013)

*Re: Alignment*

8)



Bernie


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## wa5cab (Jul 8, 2013)

*Re: Alignment*



cdhknives said:


> Okay, how do I tell if it is a up/down (wear) or left/right (can adjust) alignment issue?
> 
> View attachment 56733



cdhknives,

Here is a piece that I wrote on the Yahoo Atlas_Craftsman list about a year ago on the effect of tailstock height error. I still haven't gotten around to running the numbers to confirm my added comment at the bottom of the piece. But thinking about it for a while tonight, I still think it's true. In any case, the answer to your question above is that you can't without some other method of measuring.

***********
To give a feel for the actual magnitude of errors a small vertical tailstock to 
headstock error actually makes in finished diameter of parts turned between 
centers, especially compared to front-back offset error, here are some simple 
hard numbers.

Suppose the following:

Bed is straight and level in both planes and carriage travels in a
perfectly straight line parallel to lathe axis in both planes.
Cutter is perfectly on-center at headstock end of workpiece.
Workpiece diameter is 2.00000" (1.00000" radius, makes the calculator input simpler).
Workpiece length doesn't matter (this isn't a supposition, but a fact that
needed to be mentioned here somewhere).
Tailstock is perfectly on-centerline front to back (+/- 0.00000").
Tailstock is 0.01000" high or low (gross error even on a 60 year old Atlas).
Cutting pass is normal (right to left).
Cutter is advanced against workpiece at tailstock end to perfect touchup
(0.00000" cut).
Cutter is ideal (doesn't care about angles between its surfaces and
workpiece) and material is ideal (totally insensitive to depth of cut problems).
The vertical error at touchup at the TS end is 0.01000" (given).

The touchup point at TS end is 0.57297 degrees (ARC SIN 0.01000) around the
workpiece from the actual front of the workpiece.
The vertical error at the HS end is 0.00000" (given).
The cut radius at the HS end is 0.99995" (COS 0.57297) or a cut at the HS
end of 0.00005"

So the new diameter at the HS end is 1.99990" (from 2.00000"). Remember
that this is on a 2" diameter workpiece. However, as the workpiece diameter
decreases, the error increases significantly. For a 1" diameter workpiece,
the cut error is 0.0002" for a diameter error of 0.0004" and for a 1/2"
diameter workpiece the numbers are 0.0008" and 0.0016". So, for small angles,
the error quadruples as the diameter halves.
(added) For a 3/4" diameter workpiece,the cut error is 0.0004" for a diameter 
error of 0.0008". 

It seems intuitively obvious although I have not run the numbers that if the 
tailstock setover is adjusted using the "turn a test piece" method instead of 
the precision test bar method that it will compensate for 
any height error when you are turning a workpiece of the same diameter as 
you used to adjust the setover. But only partially so if the diameter is larger or smaller.

All figures rounded to five places and it is assumed that HP's small-angle
calculations are good to better than five places.

*************

Robert D.


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## Ray C (Jul 8, 2013)

*Re: Alignment*

+1 on wa5cab's words here... The up/down aspect of the tailstock has virtually no measurable impact on cutting diameter. If it's up/down by several thou, it only makes a difference when you're trying to drill a hole. None of my mics can reliably read past 4 decimal points. 


I too wrote-up a mathematical explanation in a different web site several years ago. Doubtful I can find it now.

If you distrust or cannot follow wa5cab's treatise then just consider that for many reasons, the whole compound, carriage and tool bit all jiggle up/down several thou as it travels -yet, shafts come out perfectly round all the time.


Ray




wa5cab said:


> cdhknives,
> 
> Here is a piece that I wrote on the Yahoo Atlas_Craftsman list about a year ago on the effect of tailstock height error. I still haven't gotten around to running the numbers to confirm my added comment at the bottom of the piece. But thinking about it for a while tonight, I still think it's true. In any case, the answer to your question above is that you can't without some other method of measuring.
> 
> ...


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## cdhknives (Jul 8, 2013)

*Re: Alignment*



Ray C said:


> Oh, I can't see in the picture how you're holding the piece... still using a jawed chuck or turning w/a dog?  How we proceed and what we can learn from the results are different depending on how the work is held.
> 
> Ray



Neither.  I took the chuck off and installed a dead center.  For the very light cuts needed for this operation it had sufficient grip to drive the rod without a dog.


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## Ray C (Jul 8, 2013)

*Re: Alignment*

OK...   What you're doing then, is a tailstock alignment test. As mentioned earlier it takes a few tries and sometimes, all you need to do is unlock the ram and relock it -and that will move things enough to make a change. Also, if you trust your ways and carriage (which is yet to be determined) you can mount a dial indicator to see how much of a change you're making.

The simple act of locking/unlocking the ram or overall tailstock clamp can move things a good bit. The lock-up method and way configuration are a couple of the critical aspects of lathes. You are getting into the meat of things...

Ray




cdhknives said:


> Neither. I took the chuck off and installed a dead center. For the very light cuts needed for this operation it had sufficient grip to drive the rod without a dog.


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## Richard King (Jul 8, 2013)

Now try the test on a shorter bar.   :thinking:


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