# Lathe Alignment



## Susquatch (Feb 12, 2022)

In @Brent H , post on miss metric, I asked about potentially using a black pipe and two replaceable collars to align a lathe head to the lathe bed. I speculated that such a bar might save me from wasting an otherwise useful piece of bar.

@Brent H , @PeterT , @YYCHM, @YotaBota , & @Tom O have all provided input on Brent's thread so I have named them here so they can provide further input if they wish without hijacking Brent's thread.

The idea of using cheap black pipe is simply to make the bar stiff without adding unnecessary weight which might deflect and affect the alignment.

I will make the assumption here that others already know how to align a tailstock. This is not about that task. This is about aligning (or testing the alignment of) the spindle to the bed.

I believe said alignment requires a cut at both ends of a test bar. Ideally, the center section of the bar is of smaller OD than the ends so that the tool bit can move end to end without cutting the center. But this is not a requirement.

Such a bar is NOT mounted in centers. It can be mounted in the spindle taper or in jaws. In either case, a cut must be made at both ends to true the axis of the bar to the axis of the spindle. However, the extent to which the axis of the bed is misaligned with the axis of the spindle will affect the OD of the two ends. It is this difference that is used to test and to determine the alignment.

@PeterT prepared some drawings to demonstrate the evaluation and I have copied his post here.



PeterT said:


> I'm talking about a shop made alignment dumb bell either from solid, or from something like a section of tubing plus separate ends to economize on material. All you need is Loctite to bond the ends. Tubing is actually desirable because it doesn't need to be cut (stress relief) & has plenty of rigidity for this application. Once you have end blanks either center drilled & slightly oversize OD ends, you mount between centers (not a chuck or collet) & take a skim cut over the OD. Preserve that infeed setting exactly, flip the bar & repeat skim cut on other side. They are now centered and parallel. Indicating on the HS side & comparing that to the TS side will indicate in/out & up/down of the TS center. No cutting is ever required beyond making the test bar.
> 
> To check spindle alignment relative to bed, the best method I know of is a precision MT taper / parallel bar.  The one I bought is MT3 so I use my MT5/MT3 ground adapter that came with the lathe. You can also use this to stick in the tail stock MT socket & do some referencing there independent of the headstock. If you have a completely parallel test bar, it must be gripped by a chuck or something & you introduce potential errors.



I'm not sure I agree with Peter's post in total but usually I find that is because I didn't understand what he meant. 

In my experience , the whole point of chucking the bar is to true it to the chuck axis. To do this cuts MUST be made. Said cuts will result in a perfect cylinder if the axis is aligned or a cone if they are not. Furthermore, measurements can be made at the tops and fronts of the bar to determine any angularity. 

Ive always found it wasteful to use a solid bar because fresh cuts must be made each time the bar is used. @Brent H has apparently had the same experience. Hence my idea of a pipe and sleeves very similar to what @YotaBota suggests, but not mounted on centers. Again, to test head to bed alignment the bar must not be constrained to the tailstock. 

I like the idea of locktite to hold the collars on, but I'm thinking screw on would be better at the far end and some kind of locking taper or even bolted connection at the near end. I'd like the replacement to be easy when they get too small.


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## Susquatch (Feb 12, 2022)

@PeterT @YYCHM .

Remember that the bar is not mounted in the tailstock. I don't want the bar to be turned around because I need to find the misalignment. That is done by measuring the difference caused by the misalignment. If it's parallel, it's perfect. Again, a fresh cut must be made each time the bar is used and each time the head alignment is adjusted.


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## PeterT (Feb 12, 2022)

_I'm not sure I agree with Peter's post in total but usually I find that is because I didn't understand what he meant._

Maybe there are 2 separate issues in your question so lets deal with aligning headstock to ways first. It does not involve the dumb bell bar.
Test bar has MT taper on one end which engages spindle MT socket. A DTI is attached to mag base attached to saddle. DTI runs along the cylindrical portion of test bar. It detects in/out and/or up/down represented by orange arrow length.  The reason why I think introducing any kind of work holding part like a chuck is because the chuck mount + jaws + test bar are potential collective error sources. I cant draw it proper but that's what lower sketch represents. DTI says head is aligned but it could be a combination of factors which masks or exaggerates. So far so good?


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## PeterT (Feb 12, 2022)

The reason why the HS must first be aligned to ways independent of TS is you could have 2 misalignment problems masking the problem. HS is cocked at angle. TS is off center, displaced to rear. But the centers are aligned & DTI would not register change. Nobody would test a lathe this way but just demonstrates trick geometry.

So many advocate Step-1 as chucking a big bar of aluminum (with no TS support of course), the bar is cantilevered. By spinning & turning the stock we introduce taper in the test bar if the HS is misaligned. Measure the inner & outer diameters shows us what direction HS is cocked & by how much. The chuck/jaws/mount don't factor because this is a rotating environment. But the downsides (in my mind) are

- you are somewhat limited by how much material stick out. A 2" diameter bar at say 3:1 is only 6" long. So you can only detect angular deviation to that length. Is 0.001 per 6" good enough? That's for you to decide. Are you absolutely positive a 0.001" larger diameter measurement at the outboard end wasn't just material beam deflection? How about surface finish? How would you disseminate if the HS was misaligned in pure yaw vs. pointed up/down in the bed. The resultant taper is a combined effect of both issues.

- So you make a sensitive, remedial lathe tweak to adjust HS. Now rinse & repeat the entire cutting procedure.

The test bar seems so much easier to me. Its precision ground, supposedly within tenths if you can verify it. Plug it into the spindle & DTI measure.


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## PeterT (Feb 12, 2022)

Some people have different spindles & might be wondering about the MT. I've annotated my lathe. The spindle is an MT5 socket.


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## Susquatch (Feb 12, 2022)

I believe I understand you now Peter.

Regarding part 1.  I guess I just don't trust a taper to be that accurate. I'd be chasing my tail if not. But a very light fresh cut will be concentric and trust worthy.

Edit - "repeatably accurate" meaning - can it be removed and re-installed such that it will be within a tenth or so each and every time? 

Regarding part 2.  I did some math regarding beam deflection.  At 18" with 1.5" black pipe, it isn't enough to worry about and won't materially affect the measurement or the alignment. I was going to do some actual deflection measurements at 24" to confirm this view. Maybe I will do that tomorrow if I get the opportunity.


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## Susquatch (Feb 12, 2022)

Btw @PeterT,  I believe I've said this before, but I really do admire your ability to whip together drawings to support your descriptions. You do a great job of that and I'm jealous!


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## PeterT (Feb 12, 2022)

18" on 1.5" diameter is a 10:1 (L to D) stick-out ratio. If we buy into conventional rule of thumb ~ 3:1-ish for steel, 4+ should consider tailstock support, 7+ consider steady (something along those lines?)
I'm not sure if the guidance is relaxed for super thin skim cuts. But 10 is a lot don't you think?

I've never turned black pipe so I can't speak with any experience there. But I can envision other factors creeping in. Deflection equations assume a perfect, homogeneous material. But most metals release internal stresses, some much worse than others & a function of skin depth. So I envision that if the unsupported end self-deflects after cutting & goes 'up-banana' by 0.001" the diameter difference would be 2X = 0.002"  apparent diameter difference assuming a perfectly parallel cut & mirror finish. To what degree its happening, that's harder to know. I've had to abandon a few grades of supposedly stable hot rolled materials over SP (stress proof) for post deflection over only 6" & that part was TS supported.

I also envision (but have no idea how to calculate) dynamic whip. To the extent the material can deflect down under it's own weight & is magnified once it comes up to rpm. Longer stickout & lower modulus are worse. So again, any measured diameter reduction has nothing to do with HS alignment & everything to do with materials & cutting influence.

The way I think of the typical (D) spindle (and maybe its wrong) our entire chuck setup is wholly dependent on the 4" vertical face & 0.5" nose taper for its alignment. These surfaces are factory ground at the same setup & I believe so is the internal MT taper. We cant use the vertical face or nose for HS alignment, but why would I dismiss 4-5" of accurate MT socket length coincident with the axis in question by just inserting an accurately ground test bar that involves no other extraneous factors?


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## Mcgyver (Feb 13, 2022)

Theoretical discussion, or a particular problem that needs solving?

Several thoughts.  This assumes correct headstock alignment from the factory, sadly in this day and age perhaps a necessary qualifier rather than a given.

imo headstock misalignment is a bit of a unicorn, almost.  Everybody's heard of it, no ones seen it.  Any reputable manufacturer is going to achieve alignment at the factory (by scraping often).   They do so to their claimed spec sheet or to a standard like Schlesingers' limits.  That's it.  You'd have to make a big effort the change that, not sure even a spindle bending crash would do so.   On inverted V ways lathes for example, you can take them apart a hundred times, and if you don't create a burr, they will go back in exactly the same alignment as from the factory.

"but its turning a taper!".  If you are getting a taper from work unsupported by the tailstock, and you haven't been in there changing the geometry, its because of bed twist and/or wear.  "but I leveled the lathe!"  Did you use a Starrett 199 or equivalent (few are equivalent imo)?   Even if you did, concrete moves and can throuw things off such that when you are chasing sub thou accuracy, a bit of bed twist can wreck your day.   Then there is wear;  You level off an unworn surface, and get the bed dead straight, but the tool path isn't straight because of wear.  When I have to get a longer cylinder very straight, I've learned how to tweak the TS end of the bed mounting bolts to fine tune and eliminate taper, for example.  Makes you feel like the Fonz giving the juke box a smack lol.  5100 lb lathe I can take a 1/4 thou taper out with a tweak of the correct floor leveling bolt

Where you do need to align the headstock is with reconditioning work.  After a bed is scraped (or ground) everything mating with it must be scraped to it.  The geometry will have changed and you must mate the headstock (and saddle and TS) to the new bed geometry, as well as achieve alignment between them, the bed and each other.

Lathe makers use precision test bars for expediency, however they are not for us.  First, you'll go broke buying them for all the lathes you'll touch in our lifetime but mainly they introduce error potential between the bar and spindle.

What most guys do, and imo the best way, is to make or procure a really accuracy ground cylinder.  to a tenth.  On small lathes I've used 1/4" dowel pin but something about the shape and size of a cylindrical sq is about right for a regular size lathe.  Chuck it however you like - 3 jaw is fine.  Its alignment does not matter. 

Then indicate it at plane near the chuck, and then at the extreme end away from the chuck.  index the spindle 180 degrees and repeat.  Use a good quality tenths indicator.  By comparing the measurements you can very accurately determine misalignment.  See diagram below - when a=b you are aligned.  I make tables and record each set of data points so I can see how I'm progressing (or not!) and it can sometimes take a frightful number of iterations.  To get things to the correct Schlesinger limit, its a function of deviation and length, the cylinder doesn't have to be as long if the measuring ability is more accurate. With a long dowel pin (longer than that in the photo) I got the little lathe in Schlesinger limit alignment. (I did however prove out the accuracy of the pin first)

Wear will mess you up, but there shouldn't be any working on HS alignment as the usual reason for doing so is scraping into a freshly scraped/ground bed.

Lastly, when indicating, its better to use some sort of sweep tool, i.e. the indicator on a spindle so can sweep the bar.  Just dragging the carriage along is sub-optimal; for example if you are aligning in Z/Y, you'd don't know if you are right on top of the cylinder as you move along it as the HS could be out in Z/X.    The second photo shows a sweep tool mounted on my alignment tool and in use scraping in a small headstock.  In this photo its set up the sweep in the Z/Y plane.


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## Susquatch (Feb 13, 2022)

A few things @PeterT .

I agree with your concerns. Keep in mind that I have not done this yet. I'm just brainstorming the concept. To date I've done exactly what @Brent H did.  I just don't like wasting a good bar like that. 

My rough math says the rigidity of the black pipe should be ok with the following caveats:

First, not cutting the black pipe, just the two aluminum collars. 

Second, no high speed, and none required. But I'm gunna noodle ways to do it without turning the lathe on. Eg - Doesn't have to be a wide collar. Could be a very thin washer you can turn by hand with a free wheeling chuck. (this might introduce some bias though.) 

Third, the reasons for 1.5" black pipe are multiple: to have some pipe inside the spindle to help everything stay in place, and  because it's about the stiffest stock you can buy for the weight and because it's dirt cheap. 

Fourth, you are absolutely right, no heavy cuts allowed. If the tool exerts any significant force on the aluminium collar at all, it won't work. 

But I'm gunna chuck up a pipe today and measure all that so we can know for sure. 

The only reason to increase the length is to improve the precision. Maybe that is chasing a false goal though.


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## Susquatch (Feb 13, 2022)

Mcgyver said:


> Theoretical discussion, or a particular problem that needs solving?
> 
> Several thoughts.  This assumes correct headstock alignment from the factory, sadly in this day and age perhaps a necessary qualifier rather than a given.
> 
> ...



All excellent points @Mcgyver .

Yes, its just a theoretical discussion for now. Basically reviewing the common knowledge and looking for potential improvements. The goal is continuous improvement. Again, maybe a false goal.

As an incredible coincidence, I just finished reading Schlesingers book last night! Many of the principles are the same or similar to the design for manufacturing used in the Auto industry. There is no point designing something that has more precision than needed, or that is possible, yet tolerances do stack up.

My lathe has six leveling screws. The head bolts to the end of the bed - not on top of it. Aligning the head to the bed is a part of normal setup.

Edit - Actually, this last point isn't technically correct. The head bolts to the bed frame and the end of the ways but doesn't sit on them.


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## RobinHood (Feb 13, 2022)

Susquatch said:


> The head bolts to the bed frame and the end of the ways but doesn't sit on them.


My Colchester and CMT are both like that.

The only adjustment (without getting the scraping tools out to correct for nod) is in yaw when using the HS adjusters. This is where cutting a test bar comes in. Factories probably get nod close enough to parallel.

I suppose adjusting the nod is relatively simple since there are usually 4 levelling feet at the HS end to “bend” the bed sufficiently right at the spindle nose to align the spindle axis in nod to the bed. Yaw is taken care of by the lateral adjustment screws.


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## Susquatch (Feb 13, 2022)

RobinHood said:


> My Colchester and CMT are both like that.
> 
> The only adjustment (without getting the scraping tools out to correct for nod) is in yaw when using the HS adjusters. This is where cutting a test bar comes in. Factories probably get nod close enough to parallel.
> 
> I suppose adjusting the nod is relatively simple since there are usually 4 levelling feet at the HS end to “bend” the bed sufficiently right at the spindle nose to align the spindle axis in nod to the bed. Yaw is taken care of by the lateral adjustment screws.



Totally agree. That is exactly how mine is adjusted too.


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## Susquatch (Feb 13, 2022)

I did some quick measurements to see what we are really talking about with the black pipe. Turns out I don't have any 1.5 pipe right now. I'll have to see if any neighbours have a scrap piece. I do have 1-1/4.  The OD on this is 1.325. 

At 24", the 1-1/4 pipe bends almost exactly 1 thou under its own weight. I just used another 24" piece at the half way point. No math required. It is what it is. 

I tried it at various degrees to see if the seam mattered. It does not. 

This is obviously a way better number than a calculated number based on material properties and geometry. Ninetheless, it does agree more or less with the calculated number I got for the 1.5" pipe at 5 tenths. 

I suppose the easiest thing to do is to take that bending into account in the alignment math. But I'd do a more precise measurement for that. 

More later. Gotta go play with grandkids.


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## PeterT (Feb 13, 2022)

Susquatch said:


> First, not cutting the black pipe, just the two aluminum collars.



So to keep things logical, everything discussed thus far pertains to Step-1: independently aligning the HS to ways which has nothing to do with TS position. It's out of the picture at this point.
It looks like you have switched gears & now talking about Step-2: aligning the TS to an established aligned HS setup. You can't skip Step-1 & go directly to Step-2. At least I think that's what you are talking about because that is the only purpose of the dumb bell style test bar, be it cut from solid or a shop made bar or purchased Edge bar if so inclined. The bar itself in this application is just a carrier, all it has to be is stiff & distortion free over time so almost anything will do. An aluminum tube is about as cheap as you can get. It weighs less & stiffness : weight ratio is probably sufficient for this purpose, but your mileage may vary. The important bits are the cut & centered dumb bell ends.

So assuming we are now talking about Step-2, here is re-work of my original sketch. It shows exaggerated TS is displaced away from spindle axis. The dumb bell surfaces are the reference datums for DTI ball which stays fixed on apron for test. Any needle discrepancy (orange arrow length) shows the in/out of TS. You can also do this vertical plane to see if TS is above/below although this is less critical to taper cutting. You can also do this with TS barrel retracted, extended, locked, unlocked to see the many exciting ways our machines can vary LOL.

If you want to get a bit more geeky, even the center drill method can be error prone at larger angles. Why? because the 60-deg dead center point will 'find a way' to engage the 60-deg cone, but its not truly coincident with the axis intersection of the dumb bell. If you want to overcome that, it's best to drill the centers with (forgot the name, parabolic maybe?) center drills which impart a curve profile to center drill so dead center is tangentially in contact. I think these were used more for taper turning for this reason. But I suspect outside the scope of discussion.


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## Susquatch (Feb 13, 2022)

PeterT said:


> So to keep things logical, everything discussed thus far pertains to Step-1: independently aligning the HS to ways which has nothing to do with TS position. It's out of the picture at this point.
> It looks like you have switched gears & now talking about Step-2: aligning the TS to an established aligned HS setup. You can't skip Step-1 & go directly to Step-2. At least I think that's what you are talking about because that is the only purpose of the dumb bell style test bar, be it cut from solid or a shop made bar or purchased Edge bar if so inclined. The bar itself in this application is just a carrier, all it has to be is stiff & distortion free over time so almost anything will do. An aluminum tube is about as cheap as you can get. It weighs less & stiffness : weight ratio is probably sufficient for this purpose, but your mileage may vary. The important bits are the cut & centered dumb bell ends.
> 
> So assuming we are now talking about Step-2, here is re-work of my original sketch. It shows exaggerated TS is displaced away from spindle axis. The dumb bell surfaces are the reference datums for DTI ball which stays fixed on apron for test. Any needle discrepancy (orange arrow length) shows the in/out of TS. You can also do this vertical plane to see if TS is above/below although this is less critical to taper cutting. You can also do this with TS barrel retracted, extended, locked, unlocked to see the many exciting ways our machines can vary LOL.
> ...



Nope, am more or less STRICTLY talking about step 1. Step 2 is easy stuff. Any discussion about step 2 is only an effort to avoid duplication. Cutting is only required in Step 1, not 2. 

Yes, I recognize that you are doing it without cutting, but I am not convinced (yet anyway) that this can be done. In my opinion, doing it without cutting would require that your MT5 (plus adapters) is ALWAYS concentric to the spindle but I doubt that it is. You will have to convince me of that or perhaps I will have to convince myself!  LOL!

The purpose of my dumbbell (as you call it) is to keep the amount of cutting to a minimum and subsequent measurements to a closely constrained location. Nothing more or less.

To avoid confusion, let's stick to the step one piece of this until the horse is dead and further flogging is pointless.

I'll remember to come back to your thoughts on step 2 when that time comes.


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## YotaBota (Feb 13, 2022)

This has gotten interesting but also kinda deep.
So, I do all the checks and balances to find my HS is nodding and/or yawing,,,, then what? I haven't found any HS adjustments for my machine, SM1120, and as a hobbiest I won't be spending a zillion dollars having it scraped to get under .001 (or what ever) in the 20" of bed I have.
Are there any options to realign the V bed HS short of scraping?
I don't imagine the majority of us have machines big enough or accurate enough to warrant those types of adjustments let alone the need. My guess would be the Myford/Atlas flat beds have the advantage in ease of adjustments over the V bed machines, go Flatbed go


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## Susquatch (Feb 13, 2022)

YotaBota said:


> This has gotten interesting but also kinda deep.
> So, I do all the checks and balances to find my HS is nodding and/or yawing,,,, then what? I haven't found any HS adjustments for my machine, SM1120, and as a hobbiest I won't be spending a zillion dollars having it scraped to get under .001 (or what ever) in the 20" of bed I have.
> Are there any options to realign the V bed HS short of scraping?
> I don't imagine the majority of us have machines big enough or accurate enough to warrant those types of adjustments let alone the need. My guess would be the Myford/Atlas flat beds have the advantage in ease of adjustments over the V bed machines, go Flatbed go


My lathe has 6 floor screws. They are used to exert pressure under the head to make minute alignment changes.

I would think some similar adjustment is possible on any lathe. Even one with just 4 feet.

That said, one can go crazy chasing unrealistic goals. Sonetimes good enough.... really is!

Lastly, there are usually numerous ways to accomplish a goal.


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## RobinHood (Feb 13, 2022)

YotaBota said:


> I haven't found any HS adjustments for my machine, SM1120, and as a hobbiest I won't be spending a zillion dollars having it scraped to get under .001 (or what ever) in the 20" of bed I have.


This was done for you at the factory.

When I cleaned up my SM1120 (and the SM1340 for that matter), the original blueing and scraping was still on the mating surfaces between the HS and the ground bed (both on the inverted V and the flat).

As you observe, if you want to / need to change the HS to bed alignment on those machines, you need to scrape them. Once aligned, there should be no reason for that to ever change in normal use.


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## Mcgyver (Feb 13, 2022)

YotaBota said:


> This has gotten interesting but also kinda deep.
> So, I do all the checks and balances to find my HS is nodding and/or yawing,,,, then what? I haven't found any HS adjustments for my machine, SM1120, and as a hobbiest I won't be spending a zillion dollars having it scraped to get under .001 (or what ever) in the 20" of bed I have.
> Are there any options to realign the V bed HS short of scraping?
> I don't imagine the majority of us have machines big enough or accurate enough to warrant those types of adjustments let alone the need. My guess would be the Myford/Atlas flat beds have the advantage in ease of adjustments over the V bed machines, go Flatbed go



its got to get a little deep so that people can understand what is really going on.  If someone really does need a headstock alignment (a unicorn) its a really big job and you're going to pay a lot or have to learn how to scrap, no matter how much the person doesn't want to.  However....if its a decently made lathe (a SM definitly is), its almost for sure not a head stock alignment issue, no matter how much it appears to be so (I hedge with the "almost" just in case the earth has come off its axis and weirdness is everywhere).

And we get things to tenth over 2 feet not a thou


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## YotaBota (Feb 13, 2022)

I was doing the "what if" scenerio, there are four mounting bolts on the HS end so there could be the ability for a minor adjustment but I'm not to concerned. Even if there is a bit of an alignment issue, the machine is still way better than I am, LOL.
I never took the HS off when I was doing the cleaning but I would guess it's the same as Robinhoods.


Mcgyver said:


> And we get things to tenth over 2 feet not a thou


What do you mean "we"- you must have a mouse in your pocket. LOL


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## Mcgyver (Feb 13, 2022)

YotaBota said:


> What do you mean "we"- you must have a mouse in your pocket. LOL



you too, if you tried scraping.  Not suggesting you should (its a bit of rabbit hole sane people are best to avoid), however while the accuracy, despite being true, sounds like a big boast, its mostly just the natural outcome of the process (accuracy of the reference flat, resultant depth of the layer of blue, the DOC, etc)

EDIT, I'd add my thinking and remarks are for SM's which are inverted way lathes (or the ones I've seen are).  As Robinhood points out others don't register on the V and are adjustable


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## PeterT (Feb 13, 2022)

Susquatch said:


> Nope, am more or less STRICTLY talking about step 1. Step 2 is easy stuff. Any discussion about step 2 is only an effort to avoid duplication. Cutting is only required in Step 1, not 2.
> 
> Yes, I recognize that you are doing it without cutting, but I am not convinced (yet anyway) that this can be done. In my opinion, doing it without cutting would require that your MT5 (plus adapters) is ALWAYS concentric to the spindle but I doubt that it is. You will have to convince me of that or perhaps I will have to convince myself!  LOL!
> 
> ...



So if we are back to Step-1 please explain how you are using the dumb bell profile test bar to verify the spindle is aligned to the ways.

[spindle picture reference] I mentioned that I have higher confidence that the spindle internal MT taper grind probably is as accurate as any other of the governing spindle surfaces because its logical (to me) they would preserve the same rotational grinding setup when ALL the governing surfaces are done - bearing OD's, journal surfaces, vertical end surface & internal socket. I don't know that for a fact but logically, why disturb the setup, remove the spindle to another setup & risk an inferior job grinding the MT5 surface? So sure, we could second guess or speculate the ground MT5 axis is not coincident with the main spindle axis, but I'll leave that to you somehow ascertain with measurements. We can just keep going down that speculation path & say the spindle axis is perfect but the nose taper & end surface is out, therefore every chuck which is mounted will always have misaligned axis. One of the purposes of MT taper is to directly plug in tooling which depends on coincident axis, so it's kind of an important surface. Could the MT3/MT5 socket adapter be out? Sure. I could have purchases an MT5 ended test bar if I were pickier. They are centerless ground so no end-centers drills are involved. Are they within a tenth as the cheesy documents state? I don't know, I don't have the equipment to test it. But I'm more confident of that end result of what I can cut in my lathe.

[headstock reference picture] This is my lathe. Other lathes are completely different, but a lot of the Asian bolt-on headstocks are generically similar. It has grub screws which bear against the HS casting lip & therefore dictate how the headstock sits in yaw axis relative to the ways. Breathing on the screws the wrong way can have dramatic influence on the HS alignment. This makes sense when you consider the short couple of the set screw distance on even a fine pitch thread. Some people have observed HS taper cutting problems post-move & as the story evolves oh, the HS was removed to get down the stairs. Or the sling was wrapped around HS & the machine did a few aerial piro's before moving from A to B. Or things shift over time.

So now if we are talking Lathe-X which does not have this adjustable HS feature, or a different feature, or HS is integrally uni-cast with bed prior to spindle bearing boring... then of course all aforementioned bets are off. So the very first thing that should be identified when this subject arises is: what kind of lathe are we talking about? My point is, some people chuck some stock, make a cut, observe different resultant diameters  & go chasing down foot level adjustment (lathe bed twist) because someone told them that's how its done, & don't even realize these screws reside on their machine. Now you potentially have 2+ independant problems, not just one. If the machine does not have HS yaw adjustment, you are left with fewer remedial options as mentioned by others in the post.


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## PeterT (Feb 13, 2022)

Susquatch said:


> My lathe has 6 floor screws. They are used to exert pressure under the head to make minute alignment changes.
> I would think some similar adjustment is possible on any lathe. Even one with just 4 feet.


When you say 'floor screws' do you mean the typical adjustable jacks (aka levelling pads) between the lathe base/stand & floor? Or some other kind of adjuster?
Unless you have something different which I'd be interested to see, I would phrase this as 'adjusting twist to the lathe bed' (not just under the head). The carriage rides along this new path & does what it does to the rotating part in cutting mode, but the HS is basically locked in a short, localized position on the bed.


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## Susquatch (Feb 13, 2022)

PeterT said:


> So if we are back to Step-1 please explain how you are using the dumb bell profile test bar to verify the spindle is aligned to the ways.
> 
> [spindle picture reference] I mentioned that I have higher confidence that the spindle internal MT taper grind probably is as accurate as any other of the governing spindle surfaces because its logical (to me) they would preserve the same rotational grinding setup when ALL the governing surfaces are done - bearing OD's, journal surfaces, vertical end surface & internal socket. I don't know that for a fact but logically, why disturb the setup, remove the spindle to another setup & risk an inferior job grinding the MT5 surface? So sure, we could second guess or speculate the ground MT5 axis is not coincident with the main spindle axis, but I'll leave that to you somehow ascertain with measurements. We can just keep going down that speculation path & say the spindle axis is perfect but the nose taper & end surface is out, therefore every chuck which is mounted will always have misaligned axis. One of the purposes of MT taper is to directly plug in tooling which depends on coincident axis, so it's kind of an important surface. Could the MT3/MT5 socket adapter be out? Sure. I could have purchases an MT5 ended test bar if I were pickier. They are centerless ground so no end-centers drills are involved. Are they within a tenth as the cheesy documents state? I don't know, I don't have the equipment to test it. But I'm more confident of that end result of what I can cut in my lathe.
> 
> ...



Let's try to keep in mind that I am scoping out an improved way to align the headstock here. I think we should avoid debating the merits of your preferred way to do it as that turns into a me VS you argument. Your method works for you and my old method (which wastes a lot of metal) works for me. 

I'm looking to move my method forward another level. I'm not trying to tell you that your method sucks. Although I do confess I probably erred in judgement by saying that I didn't trust a MT to be sufficient without making a cut. I should have just let that be and accept that you like it. My apologies. 

The method that I have used is the one outlined in numerous manuals. It first involves levelling the bed to remove twist. Secondly, it involves chucking a bar in the lathe and taking cuts end to end until the bar is clean. The next step is to take a very fine cut end to end to avoid loading the bar and influencing the results. A test dial indicator (0.0001) is used to evaluate the top runout of the bar at both ends. And a regular 0.0001 Micrometer is used to evaluate the change in diameter - if any. These two pairs of measurements tell the user how much the alignment is off. Corrections are made and another cut is made. It doesn't take very long to consume a whole bar this way. 

Yes, my method involves using 4 of the floor mounts to level the bed, and the remaining two to adjust the head alignment. You are absolutely correct to be sceptical of this way of levelling the lathe. Nonetheless, it works. Try to think if it as an inherently fine adjustment as it takes a lot to move the alignment even just a tiny bit. 

I would invite you to review the web for the methods that are used. You will find this to be the main one out there 

Now comes my "improvement". I got to thinking that you don't really need to measure more than the ends of the bar, the bar is slowly consumed by the testing process, and the bar used is normally very short which makes a precision adjustment difficult. 

So why not add "consumable collars" to the test bar and use them as cutting and measuring surfaces instead of the bar?

And why not use a longer pipe to gain resolution while simultaneously increasing stiffness (reduced bending with length). 

It's just an idea Peter. An idea for an improvement that I would like to discuss with others here. Even if you think the idea is stupid, (which it might well be) your input in that respect is valuable and appreciated. 

In the meantime, I ran across a video done by Joe Pie that demonstrates my current method.


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## PeterT (Feb 13, 2022)

@Susquatch I've tried to be as clear as I can. Its not personal at all. Its not my method or your method. Its just geometric outcome based on a particular sequence of steps. Please go back & read my post #23 again because I think you are missing some key points.

_*The method that I have used is the one outlined in numerous manuals. It first involves levelling the bed to remove twist. Secondly, it involves chucking a bar in the lathe and taking cuts end to end until the bar is clean*_*. *
What manuals? What lathe? It's critically important to define this from the outset. A lot of the older literature pertains to older lathes where the HS was essentially fixed to the bed. But you can't just jump to that conclusion & generalize. If the lathe in question is the kind whereby the HS can be adjusted/displaced in yaw independent of the bed (which many modern lathes are especially the hobby Asian variety), then this angular latitude can easily override any amount of lathe bed jacking you could reasonably impart. For example, assume 100% untwisted bed, its perfect. Viewing from top, if HS is yaw pointing to rear of lathe & you take a cut, the bar will be larger diameter on TS side for that reason alone.  Conversely if the HS is pointed to front of lathe, the bar will be smaller diameter on TS side. Are we in agreement? So the observed diameter reduction has nothing to do with bed twist. This HS alignment to bed is what I called Step-1. Now if you choose to ignore Step-1 & proceed directly to Step-2 & start twisting the bed to compensate so the bar reads equal diameters, that's an option too. But IMO it's just wallpapering over the first unresolved problem, so now you have 2 competing issues instead of what could actually be zero issues if you identify geometry in a stepwise sequence.

Now If the lathe HS is essentially fixed to the bed, by integral casting, permanently keyed, whatever - there is no Step-1. All you have at your disposal is bed twist adjustment. Beyond that its a more involved  re-build.

I've seen Joe's Apr-2019 video & others like them. His cardboard model & even his verbiage ~3:00+ is saying the exact same thing as my post #23 in different words. The headstock is presumed essentially fixed & the ways outboard of the HS are presumed variable. Tony's Oct-2016 video says much the same.


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## PeterT (Feb 14, 2022)

Abom79 Victor lathe example adjustable headstock ~ 14:00


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## PeterT (Feb 14, 2022)

This guy drives me batty but at ~11:00 another example of pivoting HS, Hermes lathe.


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## PeterT (Feb 14, 2022)

Not sure if this is like JoeP's Clausing Colchester, another example of pivoting HS.


			http://vintagemachinery.org/pubs/182/6092.pdf


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## Susquatch (Feb 15, 2022)

PeterT said:


> Please go back & read my post #23 again because I think you are missing some key points.



OK, I've read ALL your posts several times again and tried my best to do two things.

1. Figure out what you are trying to tell me. In doing so, I have assumed that you do have a good point to make. You always do.

2. I have also tried to assume that where ever we fell off, that it is my fault that it happened.

After doing so, I conclude that you are trying desperately to explain something I already know. And at the same time, I am asking a question that you are not answering. Instead you are answering a question I did not intend to ask. Without any question, this is my fault for not being clear and for saying things that caused this derailing. At least that is my self analytical conclusion.

Please understand. While I am a newbie at using a full size knee mill, I am a very old hand at using a lathe.

*Peter - I know how to align the head on my lathe to the bed. *I am NOT asking how to do that.

I confess I was critical of your MT5 mounted bar method. And this criticism probably did leave you to believe I didn't know how to align my head. This was my fault. And again, I apologize.

Perhaps worse, I wasn't clear at all about what I WAS asking. Again, my apologies. I will ask again shortly below and I'll try to be as clear as I possibly can.



PeterT said:


> What manuals? What lathe? It's critically important to define this from the outset. A lot of the older literature pertains to older lathes where the HS was essentially fixed to the bed. But you can't just jump to that conclusion & generalize.



I agree on all counts. For those who don't know how their own lathe is aligned, this is critical knowledge. You certainly can't align a head if you don't know how to do that on your own lathe.

However, I do know how mine is aligned. And again, *this is not my question. *



PeterT said:


> This guy drives me batty but at ~11:00 another example of pivoting HS, Hermes lathe.



Frankly, he drives me batty too. That said, almost all youtube authors drive me batty. So I won't hold it against him or anyone else.

Nonetheless, it is a good video to that shows some of my issues and background.

At 5:50 he explains how his lathe is aligned using the lathe cabinet feet. That is the same method as mine uses. 

Also, at 12:42 he explains how he uses cuts on a bar to evaluate his alignment. This is also the method that I use. 

But please note that there are a few problems with his method. Hopefully, I can address those as I ask my question again more clearly.

------------------------------------------

So what is the question that I am I asking? Before I actually ask, let me make a few statements.

Many machinists take cuts on an unsupported test bar to test for the correct alignment of a lathe head to the lathe ways. That is the method used in the video you posted. *This is also my method and I don't want to change it. *However, I do want to improve it. In fact, I want to improve on this method in two ways.

1. I want to use replaceable collars to avoid wasting a lot of  material on my test bar.

2. I want to use a longer test bar to improve resolution.

These are two improvements that have some challenges buried in them. My questions address these challenges.

Question #1 - How do I attach replaceable aluminium collars to the test bar in a way that makes them:  a) easy to change, b) does not introduce an interrupted cut for a fastener, c) does not weaken or reduce the rigidity of the test bar in any way, & d) minimizes any bias in the far end cut due to tool pressure during the cutting process.

Question #2 - What is the best way to compensate for the increased "droop" caused by the weight of a long test bar? I have assumed that a large diameter steel pipe had the highest resistance to bending under its own weight. I think this 2nd question is an ideal one for you @PeterT because you love to do drawings that analyse geometry. 

Further discussion:

Attaching a shouldered flange collar could be done with grub screws in the shoulder. But this makes the collars more difficult to make and requires more and bigger stock which is counterproductive to my goal of reducing the waste of good stock.

The collars could be glued on - but this would need to be removable glue to make them replaceable. 

A double sided collet of some kind could be employed to grip the pipe and hold replaceable collets.

Permanent shoulders could be used and large aluminium washers (acting as replaceable collars) could be screwed to the permanent shoulders from the side.

The collars can be thin to reduce the machining required.

But my main focus at this point has been on the bar itself. I have found through experimental analysis that a 24" long 1-1/4 inch pipe bends about 1 thou under its own weight. I suppose that a 1-1/4" aluminium pipe might bend less due to a higher strength/weight ratio. But an aluminium pipe would also bend more than a steel one under tool pressure which might be worse.

Frankly, I'm not even convinced that longer is better anyway. I've never used a long one in the past and I've never seen anyone else using a longer one. So perhaps this is mostly a tail chasing game. Or are others just more scared of a long bar whipping around, or tool pressure deflection, or or or. To me, the question is simply not simple! If it were, I wouldn't be here asking about it!


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## Susquatch (Feb 15, 2022)

Another thought on cutting the collars would be to finish my new tool post grinder and use that to do the test cuts. I "believe" that might address the tool pressure deflection issue on a longer bar.


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## thestelster (Feb 15, 2022)

This is my test bar.  It serves double duty.  For tweaking alignment of head, by chucking the left side only, or tail stock alignment, put between centers.  The bar is 8" long steel, 1.250" in diameter.  The aluminium rings are 2" in diameter 5/8" wide.  The rings ID were bored for a slip fit over the steel rod and are attached with green Loctite.  If I ever need to replace them, a little heat and they'll come off.  The head stock of my lathe sits on the bed.  There is no provision for alignment.  Hopefully the manufacturer ground and scraped the headstock for proper alignment.  If that was perfect, and the spindle bore and bearings and shaft, etc, were perfect, and the bed ways and v's were perfect, and if we bolted the lathe to a solid concrete foundation, and leveled the ways perfectly.  We just might get perfect cuts! Ha! Good luck with that!

I do not have an alignment mandrel which goes into the head stock.  And the ones that I have seen on-line are solid units.  In Dr. Schlesingers treatise, "Testing Machine Tools", he describes the construction of the test mandrels as being hollow, to reduce the influence of gravity. Therefore I can't readily measure if the headstock is out of alignment.  But even if I did and determined it was way off, attempting to scrape that would kill me. So if I've leveled my lathe as perfect as I can get, and I'm turning a slight taper, my only fix is to jack up one of the corners at the tail stock end.  Even lifting a corner 0.002" will make a difference on the cuts on my test bar. Does that mean my lathe is now perfectly aligned?  Yes, but only at the section of the lathe, over the distance between the aluminium collars.  So I can now turn a chucked bar for 5", and know that it will cut to a couple tenths or less....today.  Next month might be a different story because everything shifts.  Why did I only make my test bar 5"?  Any more than that, and chatter happened.  And besides, can you realistically turn something longer only chucked with no support.


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## Susquatch (Feb 15, 2022)

This is GREAT STUFF @thestelster. And EXACTLY the stuff I am interested in.  I especially like your collars. They are like what I had in mind. I like the green loctite too. Certainly a lot simpler than what I had in mind. I always did like KISS. To be fair, someone else suggested loctite too - just not green. Green should work. I will see. 

Your reference to Schlesingers reference is also spot on. In reviewing that section of his work, I note that he didn't even try to "compensate" for the bending due to weight/gravity. I think this warrants some additional study. In my feeble mind, I think it ought to be possible to use a calibrated calculation (a more modern concept than used by Schlesinger) to determine the impact and include it in the adjustment. I'll have to see about that as time passes. 

I am pretty sure I can go way beyond 5" without chatter. I've already been thinking about it though. A shear tool should reduce that problem and a grinding wheel should clobber it. 

Can I realistically turn something longer with no support? Of this I am certain. Yes I can. I already cleaned up the far end of my 24" pipe that way using extremely fine cuts with an extremely sharp hss bit at 70rpm. My biggest worry would be the tool catching. But again, a shear tool or better yet a grinder should fix that. 

The bigger question in my mind isn't really can I. The bigger question is why bother! I can see the point of 10 inches, but why 24?  Because I can? Not a good reason. Because it's important? I don't think so. The vast majority of my work is all within 6 inches of my spindle. Anything beyond that almost always uses a center on the tailstock. Very few exceptions anyway and even those that do - do not require precision. 

Most likely, this part of the question is just a curiosity exercise. But I like those because of what they teach me.


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## thestelster (Feb 15, 2022)

Susquatch said:


> Your reference to Schlesingers reference is also spot on. In reviewing that section of his work, I note that he didn't even try to "compensate" for the bending due to weight/gravity.


Actually he does.  See the attachment.  He says there should be some inclination upwards  and towards the operator, both at the head stock  and the tail stock.  But doesn't give an amount. Which would depend on the weight and length of the piece being turned  and perhaps the cutting forces involved.


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## Susquatch (Feb 15, 2022)

thestelster said:


> Actually he does.  See the attachment.  He says there should be some inclination upwards  and towards the operator, both at the head stock  and the tail stock.  But doesn't give an amount. Which would depend on the weight and length of the piece being turned  and perhaps the cutting forces involved.



Sorry, I wasn't very clear. I did say he didn't try to compensate. I should have said that he acknowledged that it happened but didn't try to compensate. Sorry for the misleading omission.


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## Mcgyver (Feb 15, 2022)

Susquatch said:


> The bigger question in my mind isn't really can I. The bigger question is why bother! I can see the point of 10 inches, but why 24?  Because I can? Not a good reason. Because it's important? I don't think so. The vast majority of my work is all within 6 inches of my spindle. Anything beyond that almost always uses a center on the tailstock. Very few exceptions anyway and even those that do - do not require precision.
> 
> Most likely, this part of the question is just a curiosity exercise. But I like those because of what they teach me.



puzzling it through for learning is a valid reason, but I think outside of the practical (at least imo).

What target do you have for turning accuracy?  Rivett claimed a tenth over 6 inches.  Anyone have a loftier claim?  Anyone need more than that?  Alignment to that level is can be achieved with 2" diam ground 8" long bar.  With the first 2" chucked, I did a quick calc and if the math is right (now that is risky!), the drop over 6" from gravity is 6 millionths.  Not measurable.

At 18" it becomes 1/2 a thou.

In the first instance gravity isn't a factor and you can achieve accuracy to the highest standard with common measuring tools (up to a tenth over 6'), just need a round cylinder and a tenths indicator.

Based on that, for all practical purposes, there is no reason to try for a longer bar, no one here is likely measuring to better than a tenth and gravity goes from be a non issue to a problem


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## RobinHood (Feb 15, 2022)

@Susquatch , I think I understand what you are trying to achieve with your test bar: have a shaft with replaceable / sacrificial discs on it that can easily be replaced.

Glue has been mentioned, so have the various mechanical fastening methods (flanges, set screw, etc). Another way would be a shrink fit. Cool the shaft and heat the aluminum rings. You could even have small shoulders on the shaft to push them against for a positive stop.

A hollow tube - with a plug in the clamped end - would probably have the best length to stiffness to weight ratio. I am sure there are tables or calculations that can be done to figure out the OD to ID to length ratio to find the best combo. Also, the type of tube material will be important - I am even thinking carbon fibre tube with aluminum collars glued on.

I agree that the longer the free end of your test bar is, the greater the potential accuracy. Is it really necessary? I don’t think so. As you state, anything longer than about 3xD or 4xD of any part, we always try to support it if we can. Any taper can then be removed by positioning the support accordingly.

Tool pressure and part deflection are a big concern. Not just while making the test bar, but also later after everything is perfectly aligned. So, again, is it necessary to chase 1/10ths only to later have a long part have perfectly dimensioned ends, but the Center section is oversized and there is tool chatter?

What about wear, or machine inaccuracies from the factory? You can align things perfectly for the area covered by a test bar, but if your part to be turned is outside that area, all bets are off.

A lot of these procedures were written years ago when raw materials were cheap. So turning a 2” or 4” bar of quality steel into chips just to set-up the lathe was common and, I suppose, just the cost of doing business. So I totally sympathize with you trying to find a more economical way for the hobbyist and still achieve the desired result.

At the end of the day, it is still the operator’s skill that produces a quality part. Accurate machines help in that process.


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## Susquatch (Feb 15, 2022)

RobinHood said:


> @Susquatch , I think I understand what you are trying to achieve with your test bar: have a shaft with replaceable / sacrificial discs on it that can easily be replaced.
> 
> Glue has been mentioned, so have the various mechanical fastening methods (flanges, set screw, etc). Another way would be a shrink fit. Cool the shaft and heat the aluminum rings. You could even have small shoulders on the shaft to push them against for a positive stop.
> 
> ...



Agreed on every single count except one. I don't think there is an optimal OD/ID length. Bigger OD is better - period. Shorter length is better - period. There MIGHT BE an optimal material though. It's probably carbon fiber wrap. Aluminium might be better than steel. Exotics might be better still. But $ wise, black pipe is pretty hard to beat. I aimed for 1.5" simply because I could shove it further into my spindle to adjust length. At a thou for 24", it can't be bad. In fact, well under a tenth in 12.

Yes, for me, curiosity is a worthy goal in and of itself. Otherwise, I was all done with an 8" steel bar that got whittled down each time it was used. Truth be told, that's exactly where I have been for 30 years. Happy as a lark until I saw @Brent H 's comments setting up Miss Metric.


Brent H said:


> @Susquatch - indeed, using a good Bar for just a simple adjustment is a travesty. Typically they start playing bad music and last call happens just when you are about to get the numbers ….and your “adjustment” needs another Bar …. Just saying - … LOL.



He pretty much summed up the driver for my curiosity in that one simple post. 

Mostly, this is all just one even more wasteful academic exercise. But I dearly love this kind of adventure. I dare say that curiosity has fed my family very very well in the past and I'm not about to change my behaviour any day soon. I'll probably die wondering if I'll know when I'm dead. Wasteful too but......


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## Brent H (Feb 15, 2022)

Well leave it to me to stir the pot - LOL. Sorry @Susquatch to have lead you to the rabbit hole, had you drink from the chalice of Kool-Aide and then threw you into the hole …. Alas….

For what it is worth - my first Utilathe rebuild was a long process, the lathe was a mess and it involved making many new parts including gears and also welding up gear teeth.  Needless to say, that lathe had been in a major accident.  After the rebuild I put the headstock back on and was cutting a taper. 

Before a test bar was used I mounted a D1-3 bare naked back plate and took a cross cut - I was not cutting a parallel face to the cross feed. I had to get that cut working first and then the fine tuning with the test bar. 

The Utilathe (10 and 12) use the same vee way as the tailstock for alignment and the Head stock is bolted (3 bolts - 1aft and 2 fwd) to hold things down. There is no adjustment and I was not pleased.  I ended up shimming the front far side corner and it pulled the Headstock into pretty decent alignment.  I was using a 2” bar with 5” stick out for fine tuning and got things to around .0002”

Typically if I am shooting for accuracy (like @YYCHM ‘s tailstock spindle) I will check the piece I am making well before final cuts to be sure I am not cutting a taper.  The piece I am making thus becomes the test bar and waste is avoided.


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## Susquatch (Feb 15, 2022)

Brent H said:


> Well leave it to me to stir the pot - LOL. Sorry @Susquatch to have lead you to the rabbit hole, had you drink from the chalice of Kool-Aide and then threw you into the hole …. Alas….



No worries. It is a happy adventure. I love learning. I love experimenting. And I dearly love discovering something totally new hidden among the obvious. I'm grateful to be thrown the opportunity.


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## RobinHood (Feb 20, 2022)

Here is another take on the “two ring method” for lathe alignment. The actual machining is towards the end of the video where he aligns the TS. No mention of how he did the HS to the ways - I guess he just took it the way the factory set it up on his new Lion lathe.

He makes some interesting points regarding letting the machine “settle” and rechecking it often initially.






Both my Colchester and the CMT have been sitting on 3 points for about a year now (after they got moved into the new shop) to let the beds “relax“. On the Colchester I have previously aligned the HS to the bed (the CMT not yet). I will check it again once it is sitting in its final location (on all its support feet). Then set the machines so that any coolant drains properly and call it good.


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## Susquatch (Jul 7, 2022)

Time for an update. I'm posting it here because I prefer to keep my own lathe alignment discussion and activity in one place. But ya, lots of discussion about alignment tools and methods elsewhere. 

My test bar arrived - yes, very very late. Almost so late as to be irrelevant.

I was going to start by qualifying the bar but I was simply too impatient. In hindsight, that was a mistake. 

Instead, I began by checking the level of my lathe bed. It is still perfect in the horizontal plane - no detectable twisting. My level is an adjustable unit with a claimed rating of 0.0001 over 10". Reversing the level across the length of the bed resulted in the same reading at all points - slightly tipped toward the operator approximately 4 tenths.

I don't yet know if my bed is bowed at all. Wear is unlikely as the ways are induction hardened, have been kept well oiled, and show no visible sign of wear or even slight polishing anywhere. In my opinion, it is still in virtually new condition. But regardless, I did not check it for bowing (arching) because my first interest was in a rough evaluation of the test bar.

Next, I chucked a regular steel 1.25" bar and made a 6 inch dumbbell. I would have preferred 10 inches, but 6 is what I had and I just wanted a quick and dirty test to see where the lathe is. I used a shear tool to do the final cuts on the collar ends to minimize cutting loads. (yes, I know there is still a load that must be accounted for, but again - I just, wanted a quick check.

This crude two collar test showed less than a tenth variance on both the vertical and horizontal axis as well as on diameter. I conclude that my spindle is reasonably aligned with my bed for at least the first 6 inches of the bed - maybe a bit more because the saddle sits to the right of the indicator mounting.






Next, I removed the bar and my chuck. Then I checked the runout on the inside of the MT5 taper on my spindle. There was zero movement of the tenth indicator anyplace on the taper from one end to the other. When I say zero, I mean no movement of the needle at all - it was rock solid and smooth. I've never checked it before because I've never used it. So I confess that I was very pleasantly surprised at that result. I do love my lathe.

Next, I cleaned both mating tapers, installed the test bar, and gave it a few taps with a deadblow to seat it. I did not check the fit. In hind sight, that was another bad decision.

Next, I mounted the indicator to measure bar runout. You can only begin to imagine my shock at seeing about 3 thou runout at the end of the bar.

So I removed the bar and reseated it. Same result. Next, I marked the spindle and the bar, removed it, and rotated it 90 degrees relative to the spindle. The runout moved with the bar. I repeated this several times with the same result.

I stopped all further testing at that point for the day and went to bed with a distinct bad taste in my mouth.

In the morning I decided to qualify the bar on my surface plate. (I should have done this right up front - dummy me. ) I indexed the horizontal position with a center in both ends of the bar to stop any lateral movement, and put the bar into V-blocks. To my surprise the bar was pretty concentric (plus minus a half tenth) across the length of the test section and also pretty good across the majority of the taper.  I say pretty good because there is a distinct high point (just shy of a half thou) on the taper about 3/4 of the way to the small end of the taper.  Using Dykem, that same high point seems to dominate the contact with the spindle taper. (yes, I know Dykem isn't the best thing to use. But I was out of Prussian Blue. 






FWIW, that high point shows no sign of damage or cause. It's just a random high point on the taper. I find this very odd. The bar is clearly ground and it's hard to see how that could have happened. Perhaps there is an inclusion under the surface that didn't cope well with the hardening process or that decided to swell after manufacturing. There is no sign of a ding or other impact related cause. 

My preliminary conclusion is that the bar is useless for its intended purpose as is.

I have thought long and hard about trying to fix it. It's probably not that hard to do. Some stoning at the high spot might do the trick. The bar is not designed to take a load so there is no need for high contact coverage - just location. That's my opinion anyway. 

Right now, I can only say that I am now doubly convinced that bars like this cannot be trusted for testing lathe concentricity without first testing the bar itself for concentricity of the test bar and Morse taper. I have yet to decide if it was ever even worthy of consideration for that purpose. The two collar bar is pretty darn simple and is not susceptible to errors of this nature. 

In my mind, the final word is still a two collar test for a lot of reasons. But more to the point, given that it's the final word why not just go straight there and skip right over other methods that may or may not have misleading flaws.

After I stone the bar, I'll post an update here. 

I'll also put it away for a year or so and see what happens to it over that time.


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## thestelster (Jul 7, 2022)

Susquatch said:


> I'll also put it away for a year or so and see what happens to it over that time.


But make sure it's well supported, in an environmentally controlled room, and rotate it every couple months....like you would a good cigar


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## PeterT (Jul 7, 2022)

I've stored mine in a special box labelled *S*pecial *H*ypothesis *I*nstrumentation *T*rials. Along with the 89-deg square and the 0.998" thickness 1-2-3 block


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## YYCHM (Jul 7, 2022)

Susquatch said:


> Next, I chucked a regular steel 1.25" bar and made a 6 inch dumbbell.



Why a dumbbell?  What does that accomplish?


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## Susquatch (Jul 7, 2022)

YYCHM said:


> Why a dumbbell?  What does that accomplish?



It isn't absolutely necessary. But it does help. You want an *identical* cut at both ends. If the cutting tool varies at all from the cut it makes at one end vs the other, then the measurement gets messed up by that variance. A long traverse along the entire length increases the possibility of a variance. The best way to minimize that is to only cut at the ends and not in the middle. That way you cut a bit at the far end and then when the cutter hits the center space you can just go to close end and cut again without touching the compound. Preferably, the compound is also locked.

Edit - I should add that you might wonder why not just back off the compound for the trip. Again, it can easily introduce a variance than can mess up the measurement. So you don't want to touch the compound between cuts.


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