# My lathe is turning a taper



## Pcmaker (Nov 3, 2019)

I have a PM-1127 lathe and my current project is making a replacement drawbar for my mill. It's 14 inches long, the longest thing I've ever had to turn on the lathe. 

The difference is around .015 from end to end. That's a big difference. I have the work piece supported with a live center. 

How do I narrow down what could be causing the taper? I lined up the tailstock with the headstock not so long ago. The ways is pretty level when I checked it a month or so ago. The difference between the ends of the workpiece is so large, that I don't think it's unlevel ways. 

I"m thinking maybe my center drill hole isn't dead center? How do I find out? I wanted to stick out the round bar without the live center support and indicate it, but I"m worried that it sticks out long enough that the round bar will not be straight.


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## MontanaLon (Nov 3, 2019)

How did you line up the head and tailstock? 

I have found that sometimes the tailstock alignment is best set by using an alignment bar or by turning and tuning on the current project and once it is right turning to the final dimension before moving anything.


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## Latinrascalrg1 (Nov 3, 2019)

Is the tailstock side larger or smaller then the headstock side?  Depending on which side is bigger determines which direction to adjust the tailstock, forward if its larger and to the rear if smaller ..... If im not mistaken  your lathes tailstock has an adjustment screw on the bottom rt side (standing in front on the lathe).


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## ttabbal (Nov 3, 2019)

I haven't done it with steel, but aluminum deflects enough over that length that I got all sorts of weird on a long cut like that. It makes sense, it's pretty easy to bend 10 thou in the middle of thinner aluminum bar. Put an indicator in the middle and push on the bar. It's easy to deflect it that much. 

The good news is your lathe came with a tool for that. The follow rest. 

The bad news is that it takes practice to get it to work right. I took a few long cuts before I got the hang of it. 

The question becomes, do you need it to be that accurate over the whole length? For a drawbar, I would say that you don't. I mean, it's a nut on one end and a inch or two of threads on the other, right? Perhaps I'm missing a reason why, if so, I hope to learn. I made one for the lathe spindle that is just a piece of all-thread from a box store, and a couple nuts and washers with a bushing I made to center it.


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## JimDawson (Nov 3, 2019)

Yup, sounds like your tail stock needs to be adjusted, front to back.  The other thing that can cause taper is the tailstock height is not on the spindle center line.  But you can compensate to some degree by adjusting front to back.

Getting a little deeper into the weeds here, is your head stock aligned to the ways?  Probably is, but doesn't hurt to check.


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## MrWhoopee (Nov 3, 2019)

Off-center center drill will not cause taper.


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## Pcmaker (Nov 4, 2019)

MontanaLon said:


> How did you line up the head and tailstock?
> 
> I have found that sometimes the tailstock alignment is best set by using an alignment bar or by turning and tuning on the current project and once it is right turning to the final dimension before moving anything.



I took off the chuck, put a dead center in and live center on the tailstock, aligned the tips by eye



Latinrascalrg1 said:


> Is the tailstock side larger or smaller then the headstock side?  Depending on which side is bigger determines which direction to adjust the tailstock, forward if its larger and to the rear if smaller ..... If im not mistaken  your lathes tailstock has an adjustment screw on the bottom rt side (standing in front on the lathe).



the tailstock side is smaller, and gets larger as I get closer to the headstock.

Also, could a live center cause it by not being ridgid enough? I got a cheap live center from eBay for $35

I'll align the headstock to the tailstock again later, maybe it's shifted from the last time I did it.

The taper doesn't matter much to the project I'm doing, but it's annoying when the taper can be noticeable visually.


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## Cadillac (Nov 4, 2019)

You said that you aligned the tailstock by pulling the tailstock to the chuck end and aligned center points. You should check alignment where the tailstock will be at 14” away. From what it sounds your tailstock is closer to the operator. 
 Have you tried doing it in steps. Stick out 5” from the chuck cut your OD, then pull out another 5” and repeat till you get your length.


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## Pcmaker (Nov 4, 2019)

Cadillac said:


> You said that you aligned the tailstock by pulling the tailstock to the chuck end and aligned center points. You should check alignment where the tailstock will be at 14” away. From what it sounds your tailstock is closer to the operator.
> Have you tried doing it in steps. Stick out 5” from the chuck cut your OD, then pull out another 5” and repeat till you get your length.



That's what I was thinking of doing. I'll work on lining up the tailstock first, though. I was thinking of putting an indicator to the tailstock and move it away from me about .0075


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## Pcmaker (Nov 4, 2019)

I wonder if I can use a round bar with center drillend both ends, hold it with dead center and live center and indicate along the length of it. I don't have anything more precise than 1018 CR round stock


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## T Bredehoft (Nov 4, 2019)

Pcmaker said:


> center drilled both ends, hold it with dead center and live center



That     certainly will get you a lot closer than you are now. Go for it.


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## Winegrower (Nov 4, 2019)

I just went through this with the Takisawa.   I found that aligning centers in headstock and tailstock was just not accurate enough.   I made a test bar, and that got me down to a few 001’s.   I happened, by accident, to obtain a 15” precision test bar, cut a headstock center in place to get as exactly centered as possible, and using that I could see that vertically the tailstock/headstock were right on.   With the test bar, I could just run an indicator along the (stationary) bar and precisely move the tailstock down to less than a half thou.

I would have fussed for a long time without the test bar.


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## RJSakowski (Nov 4, 2019)

.0075 would be hard to determine by aligning centers by eye.  For aligning the tailstock, I use a modification of the RDM method.  

If you mount a round bar between centers and measure runout with a test indicator or dial indicator, you can precisely align the tailstock.  You measure the maximum and minimum reading  at the headstock and take the average.  Then, without changing the indicator, compound, or cross feed, you move the carriage to the tailstock and do the same at the tailstock.  If the two averages are equal, the tailstock  is aligned.  If not, the difference is half the taper.

The only requirement is that the bar be truly round and of equal diameter at either end.  The diameters can be different but that adds a correction for the difference in diameters to the mix.  Note that this will also take into account and correct for any misalignment of the ways.


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## RJSakowski (Nov 4, 2019)

One issue that I have with the above method is that the alignment is only valid at the test position for the tailstock and the particular extension of the tailstock quill.  If the bed is twisted so that the lathe turns a taper on an unsupported bar, moving the tailstock will change the alignment.  Similarly, if the tailstock quill axis is not parallel with the spindle axis, moving the quill in or out will change the alignment.

Mr. Pete did a You Tube video where he made a test tool for the Morse taper in the tailstock where the end of the adapter was turned to a cylinder.  Using a suitable sleeve for the headstock and a test indicator, the indicator was zeroed on the surface of the cylindrical portion.  Then the adapter was moved to the tailstock, the carriage moved,  and the measurement repeated.  Any difference would be half the amount of taper at tha position for the tailstock and quill extension.  

This is essentially the same as above described method, the difference being that the procedure no longer is limited by a fixed length test bar and the tailstock and quill can be set at, or approximately at, the position used in turning the work.  A potential source of error would be if the cylinder were not perfectly concentric with the Morse taper but this can easily be checked.  If there was an eccentricity, the process could still be used by placing a mark on the adapter and measuring at the mark in either position. The tool can easily be made by drilling a socket for press fit cylindrical plug in aN MT center or starting with an MT to JT adapter and turning a cylinder to true concentricity.


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## MrWhoopee (Nov 4, 2019)

Pcmaker said:


> I took off the chuck, put a dead center in and live center on the tailstock, aligned the tips by eye
> 
> 
> 
> ...



A cheap live center will  give you chatter, might give taper that is larger at the tailstock end, but not smaller.
Aligning centers point to point by eye is not nearly close enough and does not give any indication of alignment when the tailstock is further down the ways.

I used the two collar method, here's shaft that I used. I made if from what I had lying around.




I got lucky. To my amazement, my Heavy 10L was within .0003 over 14 inches as received. I put my tools away and went out to buy a lottery ticket.

Don't fool around with this,  get it right. It may not be critical now, but it will  be.


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## Cadillac (Nov 4, 2019)

One thing to think about is even if you get the tailstock aligned it’s gonna be challenging to cut a 1/2or 5/8 rod 14” long between centers without deflection of the part. Using a followrest would help a lot.


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## Winegrower (Nov 4, 2019)

I would think the first step in all of this would be to ensure the headstock alignment with the ways is good, or else all efforts will fail.    I used the longest straightest bar I could find and ran it through the spindle with a 4 jaw chuck, centered it at the left end of the spindle and zeroed runout at the chuck.   Then, fortunately, running an indicator in the toolpost along the length of the rod (not supported by the tailstock, of course), I could see that the headstock was aligned parallel to the ways to few tenths.    

It seems to me if you have leveled the lathe to eliminate twist, aligned the headstock with the ways, adjusted the tailstock offset and height appropriately, and are still cutting tapers, a new lathe is the next step.


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## projectnut (Nov 4, 2019)

Here are a couple YouTube videos by Tubalcain (mrpete222).  The first is on how to make a test bar and the second is the completion of the bar and how to use it.


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## WarrenP (Nov 4, 2019)

Aligning the tailstock center with the spindle center will only show if it is close at that point. Plus its pretty hard to "see" a few thousands off by eye. You also need to align the them further out from the spindle to see if it is still lined up further out. A test bar seems to be the best way to find out.


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## Pcmaker (Nov 5, 2019)

I got it to within .0005 within 15" or so using regular 1 3/16" 1018 cold rolled, 20" in length. I faced and center drilled both ends, held it between 2 dead centers.

I indicated along 15" of it, occasionally turning the round bar to make sure it's somewhat concentric. I ran the indicator back and forth, moving the tailstock until I had less than .0005 of runout. It may not be a perfect set up to align the lathe, but I bet it's a heck of a lot better than what it was before.

It's always confusing when you're moving the tailstock to the direction you THINK would lessen the difference between both ends, but it goes the opposite way... until you get to the point where the needle goes the way you want it to go. I've never figured out how it does this. It also happens when I'm squaring up the mill vise.


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## Pcmaker (Nov 5, 2019)

Bah that didn't work. Now it's off by .020 going the other way, tailstock side being larger. I'm going to have to do this via cutting a section on both ends and measuring the difference, adjusting the tailstock as needed.

I sure hope my headstock is lined up with the ways, otherwise, I wouldn't know how to fix that


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## Cadillac (Nov 5, 2019)

The way I found it easiest to precisely move the tailstock was put a indicator on the tailstock so you can see the movement. Leave the piece that you just cut in the machine,adjust the tailstock .010 in the other direction and do a cut. You might be sacrificing the piece but after done your machine should be spot on, or at least at that position. I had the lock bolt that locks the two pieces together mess me up forgetting to tighten then get measurement.


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## Pcmaker (Nov 5, 2019)

I think the work piece was just flexing while I was turning, and that the indicating I did before that was correct. I'll have to mess with it some more. The work piece was around .430 at 15"... why didn't I think it wouldn't flex... that was dumb of me.


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## MrWhoopee (Nov 5, 2019)

A piece that size will end up smaller at both ends and fat in the middle due to deflection.  That's when a follower rest comes into play. We all have to learn these lessons.


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## cascao (Nov 8, 2019)

Take a look at this video
If headstock is out of alignment with bed ways, aligning tailstock will not help


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## mikey (Nov 8, 2019)

Just curious - what kind of tool are you using? If its a carbide insert then what is the nose radius? I ask because a large nose radius will cause the work to deflect more. In this instance, a follow rest is the best option.


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## Pcmaker (Nov 8, 2019)

I was using HSS with large nose radius.


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## mikey (Nov 8, 2019)

Okay, my experience with large nose radii is that they cause more deflection than smaller radii. If your tool geometry is good and the edges are sharp, a small nose radius will cut with much lower cutting forces and will therefore deflect less. If you prefer not to modify your tool then, again, use a follow rest and it will cut with a lot less taper.


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## graham-xrf (Nov 9, 2019)

This is something I will ultimately have to do when I have put my lathe together. I see there are many YouTube videos on exactly how to do this, including how to interpret the test bar measurements to then adjust the difference out in (almost) one step. The MrPete (Tubalcain) videos mentioned earlier look like all we need.

The quite sensitive test for whether the headstock and tailstock centres meet up exactly is to put a steel rule in between their points, and move the tailstock up to touch them together. If they are even the slightest amount misaligned, the rule will tilt. If the steel rule can be held between the points approximately 90° to them, all is well. If not, you can immediately tell which direction the (tiny) offset is.

However you fashion the test bar, even if it is a from a old pipe with end bungs, a key point is that the final cut on the dumbell-like ends, done between each adjustment, is a very minimal depth finishing cut deliberately to minimize the forces.


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## Pcmaker (Nov 9, 2019)

I got it to .001 in about an 8" length, which I'm happy with.

so far, doing it with the test bar I made didn't give me any success

What I did was I used about a 14" length of 1" diameter 1018 cold rolled bar. I turned a 1" length close to the head stock and a 1" length close to the tailstock. The difference was around .006

I then put an indicator on the tailstock and moved it .003 towards me.

Then I turned on the same 1" lengths, took off .010 on both sides. That got me .001 difference and I'll just leave it at that.


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## Cadillac (Nov 9, 2019)

You might be able to get that better by tightening the right screw just alittle tighter. Good job on the progress though.


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## graham-xrf (Nov 10, 2019)

Pcmaker said:


> Then I turned on the same 1" lengths, took off .010 on both sides. That got me .001 difference and I'll just leave it at that.


Great that you got it to something like good!
You did not specifically mention it, and I guess it seems obvious, but I am assuming you first cut away the bar a little deeper between the measure regions near the ends, so that during the final measure cuts, you could move the carriage from from one end to the other without needing to back out the cross slide, and then set it back.


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## Pcmaker (Nov 10, 2019)

graham-xrf said:


> Great that you got it to something like good!
> You did not specifically mention it, and I guess it seems obvious, but I am assuming you first cut away the bar a little deeper between the measure regions near the ends, so that during the final measure cuts, you could move the carriage from from one end to the other without needing to back out the cross slide, and then set it back.



I didn't cut between, but that's because I have a DRO. I zeroed the scratch passes each time on my DRO


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## graham-xrf (Nov 10, 2019)

Pcmaker said:


> I didn't cut between, but that's because I have a DRO. I zeroed the scratch passes each time on my DRO


OK to have cool stuff like that. So long as the measurements of the ends came close, you got there!
 I have to admit a retro-fit DRO is one of my ambitions, but getting my whole kit together comes first.

It occurs to me that if the DRO cut depth measures relative to the saddle, this experience also works to provide a "proof in passing" that it was all about the tailstock, and that the ways alignment was always OK.

Had there been a "ways twist" or some headstock misalignment with the ways, it might have driven you mad!


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## Pcmaker (Nov 10, 2019)

I'm going to check it again when I get home. I have OCD when it comes to things like this.

Also, I had Precision Matthews install my DRO when I bought my lathe from them. I learned this the hard way when I bought my mill and decided to get the DRO later on. It works, but you can tell it's been zombified, self tapping screws and all.


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