# Tailstock alignment questions



## calgaryguy (Apr 1, 2022)

Im aligning my tailstock by machining a piece 'between centers'. MT3 dead center in the headstock and a MT2 live center in the tailstock. Drive plate and drive dog installed per the pic below.






I've eliminated any taper on the shaft by adjusting the tailstock adjustment allen screws located on each side of the base of the tailstock.

When I was done aligning, I removed the shaft/drive dog and , out of curiousity pushed the tailstock up close to the MT3 center in the headstock and tightened down the tailstock. I then extended the tailstock quill with the livecenter in it out until it was almost touching the headstock dead center. Looking down on the two centers from right above their contact area I was surprised to see the tips of the two centers out of alignment - the tailstock tip was closer to the back of the machine by about .010-.015 ('calibrated eye measurement).

I guess I just assumed that once the tailstock was aligned using the 'turning between centers' method that I'd see the tips of the centers in very close alignment when brought together.

Am I off base here?


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## Darren (Apr 1, 2022)

did you level the lathe before offsetting the tailstock?


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## PeterT (Apr 1, 2022)

- as Darren says, lathe levelling (which really should be called lathe twist) should be verified 
- you could also check your extended TS barrel. Mount an indicator on your tool post & traverse down the barrel. Hopefully it confirms aligned parallel to bed axis. Hard to imagine it would be otherwise but confirming is better than guessing
- I find comparing centers point to point (between headstock & tailstock) is a bit coarse. Its better if you can mount a dial test indicator in the spindle, rotate it 180-deg & compare measurement on either side of your tailstock. That can be a dead center or inside your MT socket, extended, retracted, locked, unlocked.... Much more indicative of what's going on.
- after that we wonder what is different near the chuck vs away from the chuck where you had TS set up


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## YYCHM (Apr 1, 2022)

Boy you got me wondering, so I pulled my chuck and installed a MT3 dead center in the headstock and ran the tailstock up with both a dead center and a live center.  In both cases the center points kissed perfectly.

How are you measuring the taper on your test piece?


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## Proxule (Apr 1, 2022)

Coaxial indicator, Fast accurate and repeatable. Gluck


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## calgaryguy (Apr 1, 2022)

Darren said:


> did you level the lathe before offsetting the tailstock?


It was suggested to me that levelling a small/short lathe like this one really isnt necessary.


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## Darren (Apr 1, 2022)

calgaryguy said:


> It was suggested to me that levelling a small/short lathe like this one really isnt necessary.


I think you might be seeing why it IS necessary.


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## calgaryguy (Apr 1, 2022)

YYCHM said:


> How are you measuring the taper on your test piece?


Make a cut. MEasure close to head stock, measure close to tailstock. Adjust the TS 'in' or 'out' via the allen screws in the base of the TS until the delta between the two measurements is as close to zero as possible.

My 'taper' is sitting at .0003-.0005 over the 10" of bar. Measured with a good/known Mitutoyo 0-1" micrometer that I check regular with a standard.


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## calgaryguy (Apr 1, 2022)

Darren said:


> I think you might be seeing why it IS necessary.


It was actually suggested to me by a well known and respected member of this board when I visited his shop. I dont want to name names as I dont want to embroil anyone in a 'holy war' kind of discussion.


PeterT said:


> - as Darren says, lathe levelling (which really should be called lathe twist) should be verified


Ahh, lathe twist. I'll dig into this. It clearly makes sense.


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## Darren (Apr 1, 2022)

for initial setup of a lathe, level it, ie take the twist out, then chuck a bar in the chuck only, don't involve tailstock yet, take 2 collar test cuts say over 4" stickout, verifying headstock to bed alignment, then bring the tailstock in, between centers, fresh cut on headstock center to take runout out of the equation, adjust tailstock setover as neccesary. Thats my Friday night, greasy hands, third beer method.


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## Darren (Apr 1, 2022)

Lathe level, as Peter says is sort of a misnomer...its all about taking the twist out. The bed could be 2" low on the tailstock end and not cut a taper if the bed is not twisted.

Each of my lathes took several weeks to level. Its not a set and forget thing. Cast iron takes time to yield to your wishes. But it will over time.


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## PeterT (Apr 1, 2022)

Another aspect is the TS barrel extends by turning a thread of some sort. If the threads are worn there could be lateral play, exaggerated by less thread contact at extension. So the test I mentioned below can check for this too. Put the DTI probe on the end of extended barrel & gently pull & push it laterally. Put the quill lock on & off. Any needle deflection?

Also, does the clamping action of TS to bed put any unwanted movement in TS assembly? Not sure about the lathe or condition but again DTI will pick this up.

_- you could also check your extended TS barrel. Mount an indicator on your tool post & traverse down the barrel. Hopefully it confirms aligned parallel to bed axis. Hard to imagine it would be otherwise but confirming is better than guessing_


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## Susquatch (Apr 2, 2022)

@calgaryguy 

I know many don't agree on what is or isn't necessary. I think a lot of those in the unnecessary camp feel that way because there is nothing you can do about certain things with certain lathes. I am in the camp that says it best to know what you have to work with even if you can't fix it. Its not worth repeating what others have already said but it's worth repeating the potential issues:

Bed twisting, Spindle to bed concentrity (this isn't just sideways but also vertically). Spindle to tailstock offset (the taper effect), tailstock Quill to Bed concentricity, tailstock clamping deformation, way linearity. 

I'm not suggesting any of these are probable but when you find what you found there must be a reason and I am firmly of the view that you need to find out what the reason is - even if it ends up that you cannot fix it. Once you know what you have to work with you can often find ways to work around it.


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## RobinHood (Apr 2, 2022)

calgaryguy said:


> It was actually suggested to me by a well known and respected member of this board when I visited his shop. I dont want to name names as I dont want to embroil anyone in a 'holy war' kind of discussion.


It was I who suggested that “level” is relative by using the analogy of a lathe operating on a ship which is pitching/rolling in the sea.

I do realize I should have been more careful in my choice of words. As others have pointed out, “levelling a lathe” really means to “remove twist” in the lathe bed. One method is to use precision levels to detect such twist. Then use the lathe’s supports to remove any of it (if possible).

And yes, none of my lathes are “level” in my shop. The floor has 1% slope towards the front and the machines just sit there. There is obviously little to no twist in the beds, as I am able to turn parallel parts without ever even attempting to install the machines “level”. I should count myself lucky I guess.

I also agree with others about ”knowing what is happening” even though you may not be able to fix it. You can do that by measuring/evaluating your lathe. You can also just start making (non) critical parts (ie enjoy the machine) and discover the intricacies of your machine that way.


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## calgaryguy (Apr 2, 2022)

I'll have to put this off for a while as my lathe isnt in its final resting place in teh shop and I need to reorg and move some gear out to friends before I can put it in its resting spot.


RobinHood said:


> It was I who suggested that “level” is relative by using the analogy of a lathe operating on a ship which is pitching/rolling in the sea.
> 
> I do realize I should have been more careful in my choice of words. As others have pointed out, “levelling a lathe” really means to “remove twist” in the lathe bed. One method is to use precision levels to detect such twist. Then use the lathe’s supports to remove any of it (if possible).
> 
> ...


Thanks R. And I do realize that once 'twist' was mentioned that 'level' and 'flat/not twisted' are potentially two very different things. As always the 'devil is in the details'. I should also mention that my shop floor was not poured well and its full of small humps and depressions. 

And all of my efforts to date have been about investigating and learning teh machine, observing, making notes, and asking questions here. Hence my disassembly threads, making an attempt to re-align my TS after cleaning and reassembly, etc etc.


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## Susquatch (Apr 2, 2022)

RobinHood said:


> It was I who suggested that “level” is relative by using the analogy of a lathe operating on a ship which is pitching/rolling in the sea.
> 
> I do realize I should have been more careful in my choice of words. As others have pointed out, “levelling a lathe” really means to “remove twist” in the lathe bed. One method is to use precision levels to detect such twist. Then use the lathe’s supports to remove any of it (if possible).
> 
> ...



Sometimes I lose sight of this. As hobby machinists, we have machines to facilitate a full and rich life of our choosing.

Never let perfection be the enemy of the good. Enjoy what we have, enjoy making things those around us cannot make, and enjoy our machines for what they are and what we can make them be.

Thanks Robin.


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## calgaryguy (Apr 2, 2022)

Susquatch said:


> Sometimes I lose sight of this. As hobby machinists, we have machines to facilitate a full and rich life of our choosing.
> 
> Never let perfection be the enemy of the good. Enjoy what we have, enjoy making things those around us cannot make, and enjoy our machines for what they are and what we can make them be.


But without knowing my limits of perfection I cant strive to be better.  

One thing that has attracted me to the machining 'space' is precision. The kind of precision that I was never able to obtain in my woodworking hobbies no mtter how much time I spent setting up my machines. My expectations are tempered however within the context of this being a 'hobby' and that my 50 year old lathe and economically priced tooling will have its own limitations.


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## Mcgyver (Apr 3, 2022)

calgaryguy said:


> One thing that has attracted me to the machining 'space' is precision.



Thing is, the closer you look, the more you realize everything is flexible to a force applied, and there is no flat, square or parallel.  That dashes the hope that with a good enough micrometer and lathe one can be "precise" and just nail everything dead on.  There isn't really even any such thing as things being exact, its more like if you are aware of all the things going on, and you hold your tongue just so, you might have a chance at getting a part with the required tolerances.

Its why people recondition machines, trying to get them performing perfectly...err...there is no perfect, get them as close to it as is possible.  Its an effort to remove a lot of the variables that make it frustrating to get perfect parts...err parts with tolerance.


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## Susquatch (Apr 3, 2022)

Mcgyver said:


> Thing is, the closer you look, the more you realize everything is flexible to a force applied, and there is no flat, square or parallel.  That dashes the hope that with a good enough micrometer and lathe one can be "precise" and just nail everything dead on.  There isn't really even any such thing as things being exact, its more like if you are aware of all the things going on, and you hold your tongue just so, you might have a chance at getting a part with the required tolerances.
> 
> Its why people recondition machines, trying to get them performing perfectly...err...there is no perfect, get them as close to it as is possible.  Its an effort to remove a lot of the variables that make it frustrating to get perfect parts.



This was beautifully said @Mcgyver. It's far superior to my version because it says so much more in a way that everyone can understand. 

My version is: Everything moves no matter how big or how strong or how light the force. It's not if, it's only how much! 

May I quote you?


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## Mcgyver (Apr 3, 2022)

Susquatch said:


> May I quote you?



You just did   

sure, and thanks for the kind remarks


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## calgaryguy (Apr 8, 2022)

Wanted to circle back to this topic.

After inspecting my MT2 dead center for my tailstock it seemed 'off' or 'not concentric'. This is the MT2 dead center that came with my lathe. I saw new Busybee MT2 dead centers were 10 bucks so last time I was at busybee I picked one up. 

Alignment now seems much better.


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## calgaryguy (Apr 8, 2022)

I'm going to redo my 'alignment bar' machining this weekend and see how much closer the alignment is.


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## calgaryguy (Apr 9, 2022)

So I spent some time working a piece of 1" round bar with about 8" of stickout from my 3 jaw chuck (no dead/live center support) and examining the taper.

Initial taper was .030 over ~7", with the chuck end being the smaller dimension.

I started adding brass shim stock under the front right pad ( when looking from front) on the bed and taking another skim pass. 2-3 hours of this rinse and repeat and my taper is somewhere around .0005 over said 7-8" of bar.

EDIT: Added pics










I lost track of how much shim stock there is under that foot. I'm going to remove it tomorrow and measure it and then source some large pieces of the right thickness  and cut them to fit the entire foot and not just the bolt boss area. I *think* I can improve on the .0005, but I suspect once I rearrange my shop and move the lathe that I'll need to redo the 'levelling' process.


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## PeterT (Apr 9, 2022)

Going in the right direction & getting closer at least. There is a limit to seeking a perfect cylinder when cutting because the material is cantilevered, which of course it has to be for this test. So there is going to be slight material deflection on right side as the tool both cutting and deflecting the material ever so slightly. Some people advocate using aluminum because cutting forces are lower, reasonably stiff, temperature stabilizes faster, possibly cheaper as you turn it into swarf. I know it works but mostly I didn't have decent steel like maybe 12L14 of diameter I wanted to beaver away at. What I think is important is to dial in the exact same, reasonable depth of cut every pass & lock the cross feed. ie whatever is happening at the cutting edge we can only control so much, but at least by repeating we aim to be consistent.

I'm working on some graphics for lathe twist discussion which I'll post at some point. There's actually a lot of interesting things that are happening behind the scenes. Might not be able to quantify things, but maybe (hopefully) have a better understanding of what we are dealing with.

ps I always have to ask this question, especially because I don't know your particular lathe. Is the headstock 'settable' to the bed in any way? We beat this topic to death in another post but I'll just ask the question.


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## calgaryguy (Apr 9, 2022)

PeterT said:


> ps I always have to ask this question, especially because I don't know your particular lathe. Is the headstock 'settable' to the bed in any way? We beat this topic to death in another post but I'll just ask the question.


I am not sure.


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## YYCHM (Apr 9, 2022)

PeterT said:


> ps I always have to ask this question, especially because I don't know your particular lathe. Is the headstock 'settable' to the bed in any way? We beat this topic to death in another post but I'll just ask the question.



No, it is not.  The headstock casting has a dovetail that matches the bed.  Not sure dovetail is the correct term?


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## calgaryguy (Apr 9, 2022)

YYCHM said:


> No, it is not.  The headstock casing has a dovetail that matches the bed.  Not sure dovetail is the correct term?


a machined v-groove?


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## PeterT (Apr 9, 2022)

OK, well that eliminates one source of misalignment & actually makes life easier. Many of the Asian lathes are assembled with headstock bolted to bed way & factory positioned with a form of set screw or shim wedge. If that gets out of whack & spindle points north or south, then it needs to be dealt with before bed twist adjustment is addressed.


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## Susquatch (Apr 9, 2022)

calgaryguy said:


> So I spent some time working a piece of 1" round bar with about 8" of stickout from my 3 jaw chuck (no dead/live center support) and examining the taper.
> 
> Initial taper was .030 over ~7", with the chuck end being the smaller dimension.
> 
> ...



I agree with what @PeterT has said. 

When I first did mine I reasoned that a steel pipe with a fatter section at each end was a better way to do it. Pipe has a better bending performance for the size AND WEIGHT than a piece of solid steel has. 

Recently, I've been looking at what I could do to improve on the original design. I got sidetracked with milling projects, but my overall thinking is that it's good to have a bit of length to improve the measuring accuracy but not so long that it bends from its own weight. It's good to evaluate the bending and factor that into your analysis of the alignment. You can simply measure the deflection by hanging a weight at the end of the pipe. That is half the weight of the pipe itself. That measured additional deflection will be roughly the same as the bending of the pipe under its own weight. 

II also think that aluminium collars on the two ends of the pipe VERY LIGHTLY cut with a very sharp HSS tool minimizes the resulting cutting pressures and side deflection. 

I also think none of this is really necessary. But it is helpful to have a good understanding of what causes what when you are assessing the alignment of your lathe.


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## RobinHood (Apr 9, 2022)

Just thinking out loud: what about using a tool post grinder (if you have one) instead of a cutting tool for the test? Might reduce cutting forces even more.


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## Susquatch (Apr 9, 2022)

I think that's a great idea. It should leave a better surface to measure on too!


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## thestelster (Apr 9, 2022)

RobinHood said:


> Just thinking out loud: what about using a tool post grinder (if you have one) instead of a cutting tool for the test? Might reduce cutting forces even more.


Yes, but then it wouldn't be replicating a real world situation of the cutting forces involved during normal turning.


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## YYCHM (Apr 9, 2022)

calgaryguy said:


> So I spent some time working a piece of 1" round bar with about 8" of stickout from my 3 jaw chuck (no dead/live center support) and examining the taper.



8" of stick out unsupported?


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## trlvn (Apr 10, 2022)

An alternative way to check for bed twist is with "Rollie's Dad's Method of Lathe Alignment" (RDM):



			http://www.neme-s.org/Rollie%27s_Dad%27s_Method.pdf
		


Briefly, this method calculates where the actual centre of rotation is in relation to the bed by simply taking a measurement on a (straight-ish)  piece of stock held in the chuck.  First one spot and then rotating the piece 180 degrees to the opposite side.  The average tells you the distance to the centre of rotation.  Do that at the near end and the far end, and the difference between the two averages tells you how much the centre of rotation has changed relative to the bed ways.

Note that you can check both the vertical alignment as well as the horizontal alignment just by re-orienting your dial indicator.

Once the bed twist is under control, you can use the normal methods to align the tailstock.

Craig


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## Susquatch (Apr 10, 2022)

thestelster said:


> Yes, but then it wouldn't be replicating a real world situation of the cutting forces involved during normal turning.



Damn you @thestelster ! Another excellent point! The question is "Which approach is better?"

I will have to give this some thought and perhaps some research.

It also begs the age old question of how much is too much.

I always like to establish what my gut says before I dive in too deeply. Failing to do it right away, despite the risks, robs one of the opportunity to do it all.

At first blush, I think it's better to start as close to zero as possible and then factor in the various real world effects. Since the real world varies so much based on a plethora of factors (speed, feed, depth of cut, material, etc etc) factoring them in too early then requires a double change to factor them out and then factor the new ones in. Better to establish a zero and only factor in once. Aligning a headstock is not something we want to do whenever something changes.

But perhaps it's something that should be evaluated and quantified before worrying about it.

Lastly, how much fussing is warranted? Perfection for its own sake is more-or-less a waste of time. Does it really matter?

I don't mind thinking about it and even doing a few tests to evaluate it, but after all that is done, I still need to be convinced that it matters. If not, I prefer to move on to things that do. In this regard, my views are biased.


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## thestelster (Apr 10, 2022)

Susquatch said:


> Since the real world varies so much based on a plethora of factors (speed, feed, depth of cut, material, etc etc)


Yes, I agree, so I would think that you would do the test according to what your final operation will be.  If you will be finish turning, rough turning, grinding, test under the same circumstances.


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## Hacker (Apr 10, 2022)

Interesting conversation. I do not have the depth of knowledge that a lot the posters have when it come to machining or this topic but here is my thoughts on the the matter. In the end what you want is repeatability and hitting the tolerances that are required when making parts. Skill level and knowing your machine as well as machine accuracy go hand in hand to achieve this. When you are starting out machine accuracy goes a long ways to achieving good results, just don't kill yourself trying to achieve perfection. I spend hours aligning my lathe and leveling it. I achieved very good in the first couple of hours and the rest of the time I was chasing my tail trying to achieve perfect. In my opinion it was not worth it. Just my two cents.


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## calgaryguy (Apr 10, 2022)

YYCHM said:


> 8" of stick out unsupported?


Yep. Just like a couple of the videos I watched said to do. I was taking .002 passes which was fine, and I was also doing 'spring passes' before taking any measurements.


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## calgaryguy (Apr 10, 2022)

RobinHood said:


> Just thinking out loud: what about using a tool post grinder (if you have one) instead of a cutting tool for the test? Might reduce cutting forces even more.


You are killing me RH! My 'toys' budget is depleted as it is!  Seriously tho, I do not have a TPG. I'm keeping an eye out for one however.


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## calgaryguy (Apr 10, 2022)

As a general response to the 'perfection has its limits' responses above, I agree 100%. 

.030 taper over 8-ish inches was ridiculously bad. 
.0005 taper over 8-ish inches is, for now at least, acceptable and something I can work with.

Further, so much of my 'playing' and experimenting at this point is learning this lathe; its nunaces and limitations. I havent operated a lathe since high School ~35 years ago, so this is a much needed refresher. All those mental checks many of you like take for granted arent imprinted on me yet (is my tool post locked, is my feed in the right direction, is my TS locked, is my feed rate set right, did I remove the chuck key). For me this comes with repetition and practice.


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## Susquatch (Apr 10, 2022)

thestelster said:


> Yes, I agree, so I would think that you would do the test according to what your final operation will be.  If you will be finish turning, rough turning, grinding, test under the same circumstances.



Ideally yes, but...... Ain't gunna happen in my shop. I only want to check and especially adjust the alignment once in a blue moon. Most of my work has very little stickout and is done up close and personal at the chuck where this isn't a big deal unless it's way off. 

So ya, I will probably do the testing when I have the time because I am curious about it but for the most part I'll prolly be happy with a low load zero alignment. Lol!


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## Susquatch (Apr 10, 2022)

YYCHM said:


> 8" of stick out unsupported?



Yes. It has to be done that way. You need at least 8" and it MUST be unsupported. More improves accuracy. Keep in mind that you don't take big cuts and never go fast enough to create any significant centrifugal force.


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## calgaryguy (Apr 10, 2022)

I used a couple of videos for inspiration, but Quinn's (aka Blondihacks) was a solid inspiration.


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## Dabbler (Apr 20, 2022)

With respect to @RobinHood and all the other comments: 

My headstock test is on an unsupported centreless ground bar 1 1/2" in diameter and not turned, but measured at the chuck and at 12" from the chuck.  If that is good, then I measure the tailstock using a tenths indicator, then perform a 2 collar test at 24".  If they are all within reason I'm done.  

Grinding can have forces equal to turning if the grinding cut is heavy and the turning is light.  Also, I prefer to do the 2 collar test in aluminum, which is harder to grind.


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## Degen (Apr 24, 2022)

I'm going to stir the pot,  level is a mis-used term.

The biggest issue with any lathe is twist, with it alignment becomes near impossible to any form of accuracy.

As long as you don't have twist you don't have any issues, level just makes things easy to check and remove twist (along with work set up later), but as a reminder the lathe can have the twist removed and align perfectly without having to be level.

I worry less about the lathe being  level in its length but am fanatically obsessed with it being level front to back (this is twist free).

Hopefully this gives a better understanding on what alignment and leveling is.


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## Susquatch (Apr 24, 2022)

Degen said:


> I'm going to stir the pot,  level is a mis-used term.
> 
> The biggest issue with any lathe is twist, with it alignment becomes near impossible to any form of accuracy.
> 
> ...



I think it's a waste of time to try and change the world. The vast majority call it levelling. We purists can call it whatever we want so I have decided to just use my own words and clarify what I mean by that and let everyone else freak out however they want. The bottom line is that in my head the bed (both sets of ways) need to be parallel to the spindle axis. Everyone else can call it whatever they want.

What I find more amazing is that the majority of people seem to confuse tailstock alignment (taper) with headstock alignment.

Even worse, is that other experienced machinists will invariably insist on giving everyone else a lecture on the differences. And don't try to argue. Just hold still and listen cuz you are gunna get the lecture whether or not you already know. LOL!

I should add here that it's all well intended. Experienced members forget who has experience and who doesn't. And they don't have any idea what a new member knows. So they just do what they feel they should do and instinctively give the lecture. And don't bother trying to stop it cuz everything you say will use different words that have different meaning to everyone else. Prolly best to just attend the lecture.


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## PeterT (Apr 24, 2022)

Degen said:


> *The biggest issue with any lathe is twist*, with it alignment becomes near impossible to any form of accuracy.
> *As long as you don't have twist you don't have any issues*, level just makes things easy to check and remove twist (along with work set up later), but as a reminder the lathe can have the twist removed and align perfectly without having to be level.



Because of your particular choice of words & absence of pre-qualifiers, I am going to respectfully disagree. This has been discussed elsewhere on our forum, but the bottom line is you cannot lump all lathes into one bucket & make a sweeping generalization like that. The resultant conjecture is simply not true. Just so happens this came up on another forum recently & also referenced the same Blondihack video. Maybe this is the appropriate time to make a separate (maybe sticky) post on this subject because it doesn't pertain to TS alignment which can only come later in lathe setup process after HS is aligned.
I feel like we arrive at some collective level of understanding of HS alignment through discussion & pictures (a lot of work), then the subject pops up & we start all over again. So, because I'm lazy, I'll copy paste (my own verbiage snips) & see where it goes. If we go off tangent or too deep into a repetitive rabbit hole, then maybe time for a new post.



_Most well meaning folks will tell you to start jacking the lathe feet in order to alter the lathe bed twist in order to correct taper cutting. This is often called 'lathe levelling' which is also a potentially confusing choice of words. If by levelling we are talking about using a precision level incrementally down the length of the bed in order to get a sense of current twist or bend condition, that's fine. But the lathe does not have to be level left to right.

I suspect the reason people recommend to bed alteration right away is out of tradition, because older vintage lathes had their headstock integrally cast with the lathe bed. There was nothing to adjust, the spindle axis was a function of the HS line bore & bearings. However, what many seem to miss (maybe including Blondihacks on her own lathe) is that most Asian lathes are constructed differently & have their headstock bolted to the ways as my manual shows. I have heard that some manufacturers 'key' the HS & bed together but I don't know to what extent or class of machine that may pertain to. Anyways, for Asian lathes including my 14x40, which is actually quite ordinary, it has micro-adjusting set screws to tweak the HS rotation viewed from the top. This is done at factory. But if the HS has become misaligned relative to the ways, then this effect will also cut a taper even if the bed twist is 100% perfect. 

The best way to test for this is with a cylindrical test bar which has MT taper on one end to match your HS spindle socket. I bought a 24" made in India off Ebay for very reasonable cost. I was apprehensive but it is good value. They say cylindrically ground within 0.0001". I have no good means to validate that other than mic-ing down the length, but seems plenty accurate for hobby class machine HS & TS alignment work. Now with test bar inserted & cantilevered from the spindle, you can traverse an indicator down the length & this will tell you what's going on with regards to HS alignment - yawing in/out and/or pointing up/down. I have to caution you though, that breathing on the set screws can have a dramatic effect so proceed very carefully & only if you have a repeatable test bar. Maybe the factory omits mention of these adjustment screws so people don't start messing around, but that's pure speculation. With the spindle aligned to bed, then proceed to lathe twist (not the other way around).

I've read all the articles about cutting test bars & such. Nothing wrong with that & it has its place near the end of the procedure. Its just another means of verifying taper. You can save a lot of material & false readings by doing your best to initially validate geometry with test bar & indicator.



What I'm trying to convey is really quite simple. Upper sketch shows aligned lathe viewed from top. Zero bed twist. Lower picture shows the type of lathe where HS is mounted to bed & has the ability to be misaligned. It shows exaggerated HS angled toward rear of lathe, again zero bed twist. Would you concur the lower sketch would cut a tapered coupon?

This entire post is actually quite typical of many similar 'lathe levelling' posts one encounters on hobbyist forums. Its a familiar script. Someone notices they have taper cutting issue & the immediate solution offered is to jack the feet & twist the bed. The lathe type often does not even come up in in discussion as a qualifier. Or if it does, few people recognize that the HS is bolted to the ways & any misalignment there may well be the dominant if not entire source of taper cutting discrepancy. Then there is mysterious absence of the operator/parts manual even mentioning adjustment screws being there. If one has a larger lathe, say in 14" range, pulling the HS off & shimming is not exactly a trivial job although I recognize hobbyist skill sets vary. I'd certainly want to be sure before embarking down that path. Which is is exactly why a MT test bar is a valuable asset.

Just a guess on my part but maybe 20-30 years ago the chance of a hobbyist lathe being of the 'integrated' type (where no spindle alignment correction is possible) was certainly much higher than today. And yes, in that case you are stuck with what you have. Lathe twist is the only option & this presumes other factors like wear are good or minimal. But I would venture to guess a much higher percentage of hobby lathes in shops today are of the bolt-on style. Here is a popular vendor, quite typical of others including say Grizzly or other Asian importers. I count a dozen lathes from the smallest up to and including 14" swing which are bolt-on HS. Now if the factory did their job 100% and/or we have verified ourselves that HS is perfectly aligned in both vertical & horizontal plane, then we have arrived at the equivalent point of an 'integrated' lathe and hopefully relatively minor bed twist alteration may remedy remaining slight taper cutting. But if you have HS alignment problem & ignore it, and proceed to lathe twist, you are possibly attempting to fix the wrong problem or overcompensating which isn't the best solution. Of course this is a hobby so everyone is welcome to proceed as they see best. I'm just offering another perspective to the discussion.



			https://www.precisionmatthews.com/product-category/lathes/12-14-swing/
		



Have a look at the picture I included in post#4 & the related description of how a test bar can be used. I attached picture of mine. Depending on your lathe you can use an MT sleeve adapter or just just buy the appropriate MT taper ended test bar. My spindle is MT5 so I use the MT3/MT5 adapter which I have confirmed is accurate. This allows me to use the MT3 test bar for subsequent tail stock work.

Pre-qualifiers: this relates to lathes of the type with removable HS where HS deviation is possible. This also assumes a newish machine with straight ways. The beds have not eroded away a hollow close to chuck. If that's the case, all bets are off, setup can only be a tradeoff compromise relative to chuck distance. Its an additional problem. And this discussion has zero to do with tailstock alignment. The TS must not be integrated into this initial test.

Personally, I think its best to get the bed as reasonably close to begin with even if it means somewhat undoing a prior setup. Why? because this is the very same datum surface that our DTI will ride along via the carriage when measuring the test bar pointing out into space completely independent of the ways. So as best you can, confirm the bed is not bending upward or downward relative to HS when viewed from side. And also is not twisting CW or CCW relative to HS when viewed from end. Unfortunately ($) to do this right is best accomplished with a precision level.

The test bar locates snugly into the HS MT socket and the extended portion exaggerates the HS axis relative to the 'mean' initial bed axis. Traverse an indicator down the length of the bar, both along the horizontal plane & vertical plane. We are attempting to discern if HS spindle axis is pointing inward/outward viewed from top and/or upward/downward viewed from the side relative to ways. If significant axis deviation is noted and dominated by the HS being mechanically out of alignment, that issue needs to be resolved first. If its a small deviation where we are satisfied HS alignment is as close as we will ever get, then we have arrived at the point of what I'll call the where classic methods like RDM come into play. The remainder of work is addressing lathe bed twist and ideally concluding with real cutting conditions. BTW if you doubt the significance of HS deviation as a source contribution, do the simple trig calculation for yourself. Consider a measly 0.001" over the length of HS block & extrapolate to the end of test bar. It translates into a significant amount of taper that actually represents a lot of equivalent lathe bed twist to accomplish. And something as measly as 0.001" HS rotation is nothing on a set screw, mere degrees of screw rotation depending on the thread pitch.

Here is my own summary. Others may have a different perspective. Taper cutting is a function of 2 somewhat independent sources. It could be 100% HS related, or it could be 100% lathe bed deviation related, or it could be some % blend of both. Unfortunately, the sources could serve to counter/mask one another or they also could cascade & exaggerate one another. Adjustment may well be an iterative thing, but hopefully by standardizing one deviation source (ideally the one with lesser +/- limits) in order to conform the more dominant or significant source, we can proceed logically & efficiently & not chase our tails too much._


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## Degen (Apr 24, 2022)

PeterT said:


> Because of your particular choice of words & absence of pre-qualifiers, I am going to respectfully disagree. This has been discussed elsewhere on our forum, but the bottom line is you cannot lump all lathes into one bucket & make a sweeping generalization like that. The resultant conjecture is simply not true. Just so happens this came up on another forum recently & also referenced the same Blondihack video. Maybe this is the appropriate time to make a separate (maybe sticky) post on this subject because it doesn't pertain to TS alignment which can only come later in lathe setup process after HS is aligned.
> I feel like we arrive at some collective level of understanding of HS alignment through discussion & pictures (a lot of work), then the subject pops up & we start all over again. So, because I'm lazy, I'll copy paste (my own verbiage snips) & see where it goes. If we go off tangent or too deep into a repetitive rabbit hole, then maybe time for a new post.
> 
> 
> ...


Hate to say this you are chasing your tail.

Align bed on centers, no chucks to start. This ensures your slides do not cause taper as they travel.  If you do not do this first, everything else you do is suspect.  Start and worry about this first.  If you still have issues proceed with the rest otherwise don't mess with it.

Align head stock afterward with a collet if you have it, if not use your chuck(s).

Tailstock need to be repositioned as required to match head stock.

Finally most chucks are aligned with grinding.


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## PeterT (Apr 24, 2022)

Degen said:


> Hate to say this you are chasing your tail.
> 
> Align bed on centers, no chucks to start. This ensures your slides do not cause taper as they travel.  If you do not do this first, everything else you do is suspect.  Start and worry about this first.  If you still have issues proceed with the rest otherwise don't mess with it.
> 
> ...


Huh? Where in my description am I suggesting a chuck or collet being used in any aspect of alignment process? It is completely absent of a chuck or collet.
I am also saying TS alignment comes after HS/bed alignment.
What does chuck grinding have to do with HS/bed alignment?


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## Degen (Apr 24, 2022)

PeterT said:


> Huh? Where in my description am I suggesting a chuck or collet being used in any aspect of alignment process? It is completely absent of a chuck or collet.
> I am also saying TS alignment comes after HS/bed alignment.
> What does chuck grinding have to do with HS/bed alignment?


Well....Chuck 1, Chuck 2 and Chuck 3.....

I am going to suggest the the MT test bar is good for the latter half of the set up, but again  between centers is the correct way for the initial alignment, as you are potentionally adding errors with the MT test bar even if it is perfect.


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## PeterT (Apr 24, 2022)

It says Chunk, not Chuck. As in 'chunks' of text copy/pasted from my other post I referred to. Obviously very confusing, I will delete it.





In terms of the rest of your comment, I can see this is a losing battle & anymore input from me is not going to help matters. You obviously have a specific view of what's going on & that's cool. Good luck.


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## Dabbler (Apr 24, 2022)

Boy, this topic keeps blowing up.  On hobby machinist it blew up several times last year, too.

I wish the term would become 'lathe setup' or 'setting up your lathe to turn parallel  and perpendicular' instead of 'leveling your lathe'...

One post recently here or on another forum suggested that lathes turn a face slightly convex - which I have *never* seen (!!)  I have 3 lathes, and have used a dozen more, and it certainly has not been my experience.  Your experience may vary.


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## Brent H (Apr 24, 2022)

For what it is worth my two lathes are set at an incline so that the tailstock self feeds - wicked awesome for drilling holes and soooooo much easier on the tailstock advance screw......

Just saying.................

sorry...just tied up after a great ride across the seas................


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## DPittman (Apr 24, 2022)

Dabbler said:


> Boy, this topic keeps blowing up.  On hobby machinist it blew up several times last year, too.
> 
> I wish the term would become 'lathe setup' or 'setting up your lathe to turn parallel  and perpendicular' instead of 'leveling your lathe'...
> 
> One post recently here or on another forum suggested that lathes turn a face slightly convex - which I have *never* seen (!!)  I have 3 lathes, and have used a dozen more, and it certainly has not been my experience.  Your experience may vary.


I've read also somewhere that some lathes (especially small lathes) tend to face with a bit of a convex surface.  I have thought I may have observed that in the past and chalked it up to the tool bit not cutting as efficiently as the sfm decreased with the smaller diameter as the tool bit traveled from the outside diameter to the center of the work piece?


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## Dabbler (Apr 24, 2022)

DPittman said:


> tool bit not cutting as efficiently


Perhaps...  I couldn't speculate.


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## Mcgyver (Apr 25, 2022)

Dabbler said:


> One post recently here or on another forum suggested that lathes turn a face slightly convex - which I have *never* seen (!!)  I have 3 lathes, and have used a dozen more, and it certainly has not been my experience.  Your experience may vary.



Convex?  The lathe is supposed to cut concave.  Its how they (should!) come from the factory and you specifically put it there when reconditioning. 

Why?   There is no such thing as "dead on", everything is tolerances.  If you tried to make it cut at exactly 90, some lathes would be 90.001 and others 89.999, i.e. some would cut convex and some concave.  On those that cut convex, anything you faced wouldn't sit flat on the face but would rock.  Not desirable.

Its a very small amount.  Been awhile since I've done so I'd probably look it up before doing it again, but its 3-5 tenths over a foot.  Here's me checking it on my DSG as I scrape in the cross slide.  You sweep the pin in one location and move to another.


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## Susquatch (Apr 25, 2022)

DPittman said:


> I've read also somewhere that some lathes (especially small lathes) tend to face with a bit of a convex surface.  I have thought I may have observed that in the past and chalked it up to the tool bit not cutting as efficiently as the sfm decreased with the smaller diameter as the tool bit traveled from the outside diameter to the center of the work piece?





Dabbler said:


> One post recently here or on another forum suggested that lathes turn a face slightly convex - which I have *never* seen (!!) I have 3 lathes, and have used a dozen more, and it certainly has not been my experience. Your experience may vary.



I have seen it on rare occasions. I don't believe the size of the lathe matters. In fact, I don't think the lathe matters. The lathe itself wants to cut a flat face. Personally, I THINK (very dangerous thing to do) that it is caused by a variety of factors. For me, it has only happened with high strength steel. I like to use old Bolts (huge, big, and small) as stock. Grade 8 Bolts sometimes do this, but only when I use inserts not when I use HSS (another whole discussion we have beat to death before). I can always tell that it happened when the cutting bit only cuts the center portion as its drawn out too. I do not consider this to be a big issue. It isn't any different than making a long cut on small diameter stock with stick out. Tool pressure, part resistance to that pressure, sharpness, speed, depth of cut, etc etc all matter.

At the risk of sounding like a bit of an idiot though..... Is it possible that some cross slides on some small lathes become weak and lose rigidity as they are moved away from the operator? If so, I would think tool stick out would also be a factor. Just speculating here.


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## Susquatch (Apr 25, 2022)

Mcgyver said:


> The lathe isn't supposed to cut convex, its supposed to cut concave.  Its how they (should!) come from the factory and you specifically put it there when reconditioning.
> 
> Why?   There is no such thing as "dead on", everything is tolerances.  If you tried to make it cut at exactly 90, some lathes would be 90.001 and others 89.999, i.e. some would cut convex and some concave.  On those that cut convex, anything you faced wouldn't sit flat on the face but would rock.  Not desirable.
> 
> Its a very small amount.  Been awhile since I've done so I'd probably look it up before doing it again, but its 3-5 tenths over a foot.  Here's me checking it on my DSG as I scrape in the cross slide.  You sweep the pin in one location and move to another.



I considered commenting on this too but figured someone like you would blow it all out of the water by adding a comment like: How would you set that up to compensate for various tool stick outs that ride a different part of the cross-slide wave? LOL! 

Just pulling your chain. No need for any big convoluted explanation. Unless you can't help yourself......


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## Mcgyver (Apr 25, 2022)

Dabbler said:


> Boy, this topic keeps blowing up.  On hobby machinist it blew up several times last year, too.



Yes, one of the classic machining tinder boxes.  There are literally a lot of moving parts and tons of variables.

When you make, or at least remake which is what reconditioning is, the geometry of a machine, you need to follow a process that is exacting.  There is not much equipment required, but if you don't have the  right equipment, you get it, e.g. a Starrett 199 master precision level.   Its different if you are just trying to set up a lathe; it's not realistic to say you have to spend $400-500 (and that's used) for a 199.

Which leads to a problem.  I don't think I've used or seen a lathe upclose where headstock isn't solidly registered.  They have all had inverted V ways or are pinned.  You can rely on it (or least you could in the past) coming from the factory correctly aligned. This eliminated HS alignment as an issue.

One thing I learned here is that is often no longer the case.  After watching how SM did it over a few days, I can see why manufactures would see it as a huge cost savings not producing lathes in this manner, but imo its a real disservice.  SM had three guys full time scraping HS, TS and carriages in to the ground bed.  Its imo the right way, but it is expensive.

Nevertheless, if this is your the current reality, you can't solve this problem without having a way to detect twist separate from HS misalignment.  I haven't read everything that is here, but this challenge is no different than that faced by the person reconditioning the machine.  The correct procedure is to remove the bed twist via leveling before working on scraping the HS in (HS alignment) because if you don't, any reading (or tests cuts) you make with the carriage moving over the bed, will be erroneous if bed has twist.  If you don't have a 199, use the best you've got.

You do have an additional problem: wear.  Wear can mean even with zero twist in the bed, relying on the carriage travel for detecting things relative to the headstock introduces error.  There is little you can do about this, but one technique is to use a Kingway (or my version of it shown below which I think has several improvements) to slide along unworn surfaces.  This is better than nothing and good for surveying as well, as advocated by scraper Richard King.  (Having seen lathes been made, I do disagree with him as to how perfectly reliable these surfaces are or how exact their vectors matches those of the original ground surface as, at least at SM, they were done on different machines and setups than the way grinding).

A couple of other ideas.  The best way to align the headstock, with the bed first leveled and a reliable surface to move along, is to mount a precisely ground cylinder, like a cylindrical square in the lathe.  I say best because the error introduced with workholding doesn't matter.  Weight reduced (holes) and a few inches in diameter is ideal.  Just put it in the three jaw, alignment does not matter.

You take a reading at the chuck, then at the end - two planes.  Then you rotate it 180 degrees and do so again.  Looking at the differences between them tells the story.  In my diagram, if A=B, its aligned.  When scraping of course you have to do this in two planes, ZX and ZY but for checking alignment only ZY is looked at.  Using the A=B difference method eliminates the need for test bars and eliminates any source of error in mounting - even the taper spindle mount introduces some error.  You also want to sweep the indicator, not drag it along the work which can introduce error as the work may be going up or down hill in the other direction - see photo of sweep tool.

Despite all this, turning a long cylinder parallel to few tenths remains a BIG challenge.   The only time I might take a test cut for alignment is with this type of job....wear, tailstock quill clearance and concrete slabs moving making things somewhat "dynamic".  This is where figuring out what mounting bolt to tweak a few degrees turn pays off


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## Mcgyver (Apr 25, 2022)

Susquatch said:


> I considered commenting on this too but figured someone like you would blow it all out of the water by adding a comment like: How would you set that up to compensate for various tool stick outs that ride a different part of the cross-slide wave? LOL!
> 
> Just pulling your chain. No need for any big convoluted explanation. Unless you can't help yourself......



You lost me on that one.  I was describing how a lathe should be set up, has nothing to do with tool overhang afaik


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## Susquatch (Apr 25, 2022)

Mcgyver said:


> Yes, one of the classic machining tinder boxes.  There are literally a lot of moving parts and tons of variables.
> 
> When you make, or at least remake which is what reconditioning is, the geometry of a machine, you need to follow a process that is exacting.  There is not much equipment required, but if you don't have the  right equipment, you get it, e.g. a Starrett 199 master precision level.   Its different if you are just trying to set up a lathe; it's not realistic to say you have to spend $400-500 (and that's used) for a 199.
> 
> ...



I like this very much!


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## Susquatch (Apr 25, 2022)

Mcgyver said:


> You lost me on that one.  I was describing how a lathe should be set up, has nothing to do with tool overhang afaik



Your description was good. I was mostly having fun.

The issue I was poking at is the fact that a cross slide with ways scraped to cause a tenths off course travel would cause the tool to follow that slight curve too. But depending on where the tool, tool holder or tool post are mounted on that curve, they will have a slightly different path.

Deliberately eggagerating, if the tool is at the center of the part BEFORE the cross slide even starts moving, then the tenths adjustment will have no effect. If the tool assembly is so short that the cross slide is at the far end (assuming that was even practical), the same effect cuts in. To work properly, I think that the scraping offset must coincide with the tool on-center. Since that depends to some extent on tool hangout, I wonder why it needs those few tenths at all......

Keep in mind that I'm not arguing. I'm only curious about it and wanting to learn something.

It might also help to know that when I was first contemplating the issue (before your post) I was thinking in terms of a small or weak or worn Cross-Slide that had some "wow" in its travel.


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## Mcgyver (Apr 25, 2022)

Curve?  there's no curve....the cross slide ways scraped straight but at a slight angle, so anything above the,  compound, tool, tool post etc should move along the same straight vector.  

Maybe the issue is calling in convex, slightly misleading.  Everyone calls it that, but technically its really not convex (which would have a curve), but a very very squat indented cone shape.


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## Susquatch (Apr 25, 2022)

Mcgyver said:


> Curve?  there's no curve....the cross slide ways scraped straight but at a slight angle, so anything above the,  compound, tool, tool post etc should move along the same straight vector.
> 
> Maybe the issue is calling in convex, slightly misleading.  Everyone calls it that, but technically its really not convex (which would have a curve), but a very very squat indented cone shape.



See. That splains it perfectly! I had been thinking waistline curve. 

But it raises another question in my curious mind. What is the purpose of that VERY VERY VERY VERY VERY squat indented cone? Wear compensation?


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## Mcgyver (Apr 25, 2022)

Susquatch said:


> See. That splains it perfectly! I had been thinking waistline curve.



Who told?  Lets leave waste line curves out of it.....starting my diet today



> But it raises another question in my curious mind. What is the purpose of that VERY VERY VERY VERY VERY squat indented cone? Wear compensation?



Now I have to quote myself  



> Why?   There is no such thing as "dead on", everything is tolerances.   If you tried to make it cut at exactly 90, some lathes would be 90.001 and others 89.999, i.e. some would cut convex and some concave.  On those that cut convex, anything you faced wouldn't sit flat on the face but would rock.  Not desirable.


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## Susquatch (Apr 25, 2022)

Mcgyver said:


> Now I have to quote myself



Sorry about that. Yes you did say that. 

My only excuse is that you said that back when I still thought we were talking waistlines. So it didn't compute under the fat cone scenario either. Just my stupid brain latching onto possibilities and lack thereof. 

Then again, if the fat cone "biases" (good choice of words eh!) the tolerance to the concave side, why wouldnt fore/aft placement of the cutting tip relative to the minor axis of of the fat cone affect that too? 

Just a thought here - if it wasn't really a fat cone but rather more of a very very very very very (LOL) slight inward angle, it would also cut a concave as long as you never cut past center - which only an idiot would do - unless their lathe was in reverse.


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## Susquatch (Apr 25, 2022)

Hmmmmmm...... I just answered my own question. 

If said fat cone is in the saddle ways, not the cross-slide, then the minor axis could always be on the lathe centerline. That way both forward and reverse would do that and always be where you want it no matter what the tool hang out was. 

So...... Another question. Could it be that small EXPENSIVE HIGH QUALITY lathes anticipate this effect and being so light the effect might be worse so a high quality small lathe has an even fatter cone deliberately built into it to compensate for the even wider tolerances?


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## Susquatch (Apr 25, 2022)

This was a really great discussion @Mcgyver. I learned something totally new. I'll have to take a very careful close look at how my own lathe is setup.


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