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Tailstock alignment questions

C

calgaryguy

Chris
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.

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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?
 
- 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
 
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?
 
YYCHM said:
How are you measuring the taper on your test piece?
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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.
 
Darren said:
I think you might be seeing why it IS necessary.
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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
Click to expand...
Ahh, lathe twist. I'll dig into this. It clearly makes sense.
 
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.
 
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.
 
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
 
@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.
 
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.
Click to expand...
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.
 
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).

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.
Click to expand...
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.
 
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).

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.
Click to expand...

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.
 
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.
Click to expand...
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.
 
calgaryguy said:
One thing that has attracted me to the machining 'space' is precision.
Click to expand...

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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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.
Click to expand...

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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