Tail stock alignment

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Mr Ron
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Tail stock alignment

Post by Mr Ron » Fri Oct 25, 2019 4:46 pm

I've owned my Sheldon 11" lathe for over 30 years and have never checked tail stock alignment. This is because I rarely turn between centers; but now I feel I should check alignment just out of curiosity. I know how to set up between centers, take a finish cut and measure diameters at each end and DTI readings at both ends. This will set the tail stock from front to back (Y). But, how do I check alignment from top to bottom (Z). I thing alignment has to be perfect in both Y and Z directions. I'm assuming the Z axis was set at the factory. Do I need to check on the Z axis or accept it as having never changed. If it needed to be realigned, how would I go about doing that? I would guess use shims between the moveable top part of the tail stock and the base.
Mr.Ron from South Mississippi

John Evans
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Re: Tail stock alignment

Post by John Evans » Fri Oct 25, 2019 5:16 pm

If you can get the diameter within .0002 or so over 6"in Y do not worry about the height !
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John Hasler
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Re: Tail stock alignment

Post by John Hasler » Fri Oct 25, 2019 5:46 pm

In standard notation the axis that the cross-sllide runs parallel to is X. Z is the axis of rotation of the spindle. Y is what you are calling Z.

When turning a small movement of the tool up or down results in very little change in depth of cut so a tiny tilt to a part being turned between centers causes no measurable taper. A drooping tailstock ram can still cause problems, though. It can put you far enough off center to give you a bad finish at the far end on a small part and it can cause problems with drilling (here the angle matters as well as the height.)

After you have your tailstock set up front to back put the DTI on top of the part and measure the difference between the ends. Since you know the part diameter is the same at both ends the difference is in the tailstock.

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SteveM
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Re: Tail stock alignment

Post by SteveM » Fri Oct 25, 2019 8:14 pm

Misaligned tailstock can cause a reamer to bore out a tapered hole. Don't ask how I know.

If your bed is worn, bringing the tailstock up to the headstock and matching the center heights and offsets may not give you a true reading, although it can get you in the ballpark.

If you put a ruler between centers and make the centers touch, any misalignment will cause the ruler to tilt, just like when setting tool height.

Steve

pete
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Re: Tail stock alignment

Post by pete » Sat Oct 26, 2019 12:02 pm

Measure as accurately as possible (10ths if you can) the end diameter of your tail stocks quill. Then turn and face a piece of scrap material in a chuck to as close as that diameter as you can. Move the carriage up tight to the head stock then slide the tail stock up to the carriage. Extend the quill until it touches your turned piece. Measure the diameter across BOTH pieces in the vertical direction. Your turned test piece doesn't have to be exact since simple math of addition or subtraction can still provide accurate results. This test will only give you the results of the tail stock positioned on that spot on the lathe bed. It may or may not be highly worn and throwing your test results off. And this test assumes your tail stocks MT is and was machined and ground exactly central to the quills O.D.

One other test would be to position the tail stock at the far right hand side of the bed, lock it down using your average amount of torque, move the carriage back to almost touching the tail stock, then extend the tail stocks quill and use the carriage to run a dti along the top of the quill checking for how much it's pointing down hill. And after 30 years I'm confident it will be pointing down hill due to wear on the tail stocks base. The front always wears first and that wear tapers off to the rear. So the quill will be pointing down hill. It might be possible on your lathe to shim between the tail stocks two pieces and get it back on the head stocks C/L. Better would be to scrape the tail stocks base ways back to being square and true and then shim the tail stock back to the correct elevation. The tail stock being to the exact same C/L height as the head stock is of less importance than it's in/out C/L location. What is important is that any tool used in the tail stock is parallel and true in the horizontal plane to the lathe bed. As others have mentioned, pointing up or down can cause serious issues while drilling and reaming. And if the height alignment is out enough, spot drilling with center drills becomes impossible due to the drill tips being broken off.

Mr Ron
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Re: Tail stock alignment

Post by Mr Ron » Sat Oct 26, 2019 1:24 pm

Thank you for a very in-depth explanation. I know I always come to the right place.
Mr.Ron from South Mississippi

pete
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Re: Tail stock alignment

Post by pete » Sat Oct 26, 2019 3:50 pm

To be fair Ron, how to run tests for machine tool alignment should come with an automatic surgeon generals warning about it being possibly damaging to your short term mental health. :-) I'd suggest you figure out what mood is best for you, either your having an already really good day or a bad one before checking any machine for it's wear and alignment. I was a whole lot happier with my machines when I knew a lot less about howda check em. :-(

At least your starting with a used but still very well made machine so that's going to help. There's some unbelievably poorly made off shore machine tools being sold today. I owned one where I still can't figure out how they machined and ground it that far out without doing so on purpose. Yet the same machine still gets good reviews on every hobby forum post about it I've ever seen. So they only made one single bad one?

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liveaboard
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Re: Tail stock alignment

Post by liveaboard » Sat Oct 26, 2019 3:53 pm

pete wrote:
Sat Oct 26, 2019 3:50 pm
I was a whole lot happier with my machines when I knew a lot less about howda check em. :-(
That's just what happened to me...

pete
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Re: Tail stock alignment

Post by pete » Sat Oct 26, 2019 4:06 pm

LOL, I can relate all too well Liveaboard. Whoever invented the phrase "ignorance is bliss" must have had a home shop. :-)

Mr Ron
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Re: Tail stock alignment

Post by Mr Ron » Sun Oct 27, 2019 9:39 am

pete wrote:
Sat Oct 26, 2019 3:50 pm
To be fair Ron, how to run tests for machine tool alignment should come with an automatic surgeon generals warning about it being possibly damaging to your short term mental health. :-) I'd suggest you figure out what mood is best for you, either your having an already really good day or a bad one before checking any machine for it's wear and alignment. I was a whole lot happier with my machines when I knew a lot less about howda check em. :-(

At least your starting with a used but still very well made machine so that's going to help. There's some unbelievably poorly made off shore machine tools being sold today. I owned one where I still can't figure out how they machined and ground it that far out without doing so on purpose. Yet the same machine still gets good reviews on every hobby forum post about it I've ever seen. So they only made one single bad one?
I believe I got a lathe in almost pristine condition. According to records, it came off a navy LST. It came with all the accessories that are supplied to contract supplied machine tools to the U.S. Navy. The ways still have the scrapping marks. It had no signs of being abused or heavy use. Having spent over 50 years working on Navy ships, I observed machine shops onboard ships got little use and kept in good condition. The 4-jaw and faceplate look like they were never used. The 3-jaw shows it has been used, but also shows little wear. Maybe I'm looking for trouble where none exists. I did offset the tail stock many years ago when doing a taper, but never checked it since.
When center drilling, the center drill tends to "wiggle" a bit, so I take very light bites to center the drill;I suspect it may be out of alignment

My Sheldon is my baby and I will never let it go. It deserves a place in my living room :)
Mr.Ron from South Mississippi

pete
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Re: Tail stock alignment

Post by pete » Sun Oct 27, 2019 11:16 am

Being Canadian I obviously don't have any first hand experience with the U.S. military Ron. But from what I've picked up through reading, all of the military services and especially it seems the Navy doesn't fool around about maintaining there equipment in first rate condition. So it sounds like you got a real nice and very lightly used lathe. And got it before it was stored outside if what I've read is an all too common practice for precision machine tools. :-(

Given Sheldon's reputation it's a pretty safe bet your tail stocks MT will be concentric to the quills O.D. so side to side checking is easy. Use a magnetic base on either the chucks face of the face plate then set an indicator tip to touch the side of the TS quill. Rotate the chuck or face plate so the indicator tip runs from the front to back side of the quill and adjust the tail stocks off set until both readings are the same. Ideally..........it's also important there's no twist in the lathe bed end to end since that affects your readings and if it's there you can center the TS quill by the indicator yet it still won't be on the head stocks C/L. So if you've got a sensitive enough machinist's level then getting the bed square and true would be the first step. And VERY IMPORTANT, what you can't do is check the tail stocks vertical alignment by swinging an indicator around from the head stocks spindle. The effects of gravity will ruin your readings by at least .003" or more just from rotating even a light weight dti from the top of the quill to the bottom. The first time I ran that check I didn't know about that happening and got fooled for a couple of hours playing with shims until I finally clued in about what was happening.

Mr Ron
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Re: Tail stock alignment

Post by Mr Ron » Mon Oct 28, 2019 10:49 am

pete wrote:
Sun Oct 27, 2019 11:16 am
Being Canadian I obviously don't have any first hand experience with the U.S. military Ron. But from what I've picked up through reading, all of the military services and especially it seems the Navy doesn't fool around about maintaining there equipment in first rate condition. So it sounds like you got a real nice and very lightly used lathe. And got it before it was stored outside if what I've read is an all too common practice for precision machine tools. :-(

Given Sheldon's reputation it's a pretty safe bet your tail stocks MT will be concentric to the quills O.D. so side to side checking is easy. Use a magnetic base on either the chucks face of the face plate then set an indicator tip to touch the side of the TS quill. Rotate the chuck or face plate so the indicator tip runs from the front to back side of the quill and adjust the tail stocks off set until both readings are the same. Ideally..........it's also important there's no twist in the lathe bed end to end since that affects your readings and if it's there you can center the TS quill by the indicator yet it still won't be on the head stocks C/L. So if you've got a sensitive enough machinist's level then getting the bed square and true would be the first step. And VERY IMPORTANT, what you can't do is check the tail stocks vertical alignment by swinging an indicator around from the head stocks spindle. The effects of gravity will ruin your readings by at least .003" or more just from rotating even a light weight dti from the top of the quill to the bottom. The first time I ran that check I didn't know about that happening and got fooled for a couple of hours playing with shims until I finally clued in about what was happening.
Thanks. Good advice. I have seen machines at a shipyard sitting out in the elements and turning to rust; breaks my heart, but the precision has been lost and so they are moved out of the shop to make way for a new machine. Sometimes the size of the shop doesn't allow an old machine taking up valuable space on the floor. The old navy ships (battleships, carriers, repair) had extensive machine shops where they could replicate and repair parts for the ship's operation. I understand machine shops on ships were more like hobby shops for the crew than for doing ship work. There is a limit as to how much can be done by a more-or-less inexperienced shipboard machinist. When one thinks of a machinist, one conjures up a vision of a guy in his 50's. On ship machine shops, all I ever saw were young sailors in their teens and 20's and the machine shop was a place to just hang out.
Mr.Ron from South Mississippi

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