Sorry I just realise that Robertisheets has already posted something similar..
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1st you need a test bar which is a round bar 6-12 in. long with centers on both ends hardened and the od is ground to a tolerance of +or- .0005 or better .0001. you can make 1 if you have access to a full shop or you can buy 1 from Travers Tool or McMaster Carr. if your head bearings are tight and the ways are not beat up. take a stone to smooth out nicks and dents on the ways and the bottom of the tail stock put the bar between centers put a dial on both ends and there are adjustments on the tail per the manufacturers instructions that you can download from them. you can find this on youtube look up "using lathe test bar" that should get you started. that's the best I can help you unless you live in wi. usa Jimbo
I've owned several old lathes, most have had hard lives long before I got hold of them. What I usually do is to start off with checking to see if the head stock is anywhere near in alignment. first the spindle bearings would need to be adjusted if they are the type that can be adjusted if old poured Babbitt bearings shims may have to be taken out and the bearing scraped to round or re bored using an external boring bar attachment which would have to be mounted to the ways and centered from both ends. It is usually preferable to strip the ways of the head stock the carriage and the tail stock and get the ways trued first but this process of completely refurbishing is neither quick nor for the faint at heart.
assuming the spindle on your lathe is already running close to true, and you have decent ways,and the chuck is is good condition. You can chuck up a piece of stock and simply turn it to a point 60° would be a nice number since many dead centers are of that angle then use the buttons that Marv described or use the test bar mentioned above. I like the idea of the button method with this note. with buttons and dead points in place check the tail stock with the quill fully retracted then with it fully extended if both reading are the same your job is done, Another variation to this would be to chuck a piece of stock preferably a piece that is ground and polished leave sufficient amount protruding from the chuck in order to turn the same MT size as your tail stock has then part it off with enough of the cylinder surface remaining on the part you just made. insert that into the tail stock then perform the same measuring technique as with the buttons.
If you are not comfortable in making your own tapers then bars can be purchased that already have the taper machined on them,You would simply part it off like I mentioned.
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You should also make sure the lathe is level which would be checked most accurately with a machinst level across the ways near the headstock and also tailstock. You could get the tailstock in alignment with the headstock as has been mentioned before but then if you center drill something and then extend the stock out quite a ways, such as almost lathe capacity and turn until cleaned up and check for taper. If you do not have access to a precision level and there is taper, you at least need a good dial indicator. Set the indicator on the same plane as the cutting tool and adjust leveling screws which should be sitting on metal pads with a countersunk hole for the screw. When adjusting, only move a thousandth or two at a time and let settle for a day or so before making any more adjustments for level. Take another cut and see what changed. If you like the change, keep moving in the same direction. When setting up indicator you need to have slight pressure on the needle, you can often push or pull on tailstock and see slight movement of needle depending on how robust your lathe is. Good luck.
I'd offer reinforcement to utilizing buttons as a starting point.
However, with a decent length bed, buttons won't reflect error that surface on a longer part. Due to imperfection of wear and out-of-plane ways, and leveling of the machine itself. That's where a dog driven proof rod on centers will. "Out-of-plane" has to be corrected both along and across the ways. Straight and round turning will not occur over bed with twist.
Marv is correct, single point boring centerdrill recess and turning an outside diameter of short length [each end] will be concentric to greatest degree possible. Chuck runout is then reduced or not an issue. I'd be tempted to mark bar's relation to chuck #1 jaw, and that both ends coincide.
Then make a wooden box to store it in; ideally supported 1/3 [one third] from each end. If you suspect the bar sags in use, that is corrected by a rest; either steady or follow variety. Then you'll get good results setting up in the position you intend to work.
AND, test bar isn't restricted to occupying the chucked end and center. Set the bar chucked and steady rest accurately, then pull chucked portion into steady and free end to center point elsewhere along bed for indicating.
Last edited by Toolmaker51; 05-07-2017 at 10:49 AM. Reason: Lost count of helpful edits...after all, it's Sunday!
...we'll learn more by wandering than searching...
As I not always understand all explained, my english is sometimes not sufficient, it's just something to remember, it can take a lot of time for controlling all parts, as you can have an error in the centering of the cone which can be controlled with a well centered MC… with a 100mm. part, a second error can be with an out of round tailstock etc., you can have at least 8 or 10 possibilities of an error, controlling all parts is a big time consumer.
With a lathe as the Schaublin with a trapezoidal centering, there are less possibilities, but what occurs often on second hand lathe is you have parts with a difference in numbers of mounting, and it's a headache to solve such errors, the system with the two reference diameters give only a solution for a given position, and not for example when using a collet system.
For me the alignment of a revised lathe is the more time consuming operation to make and you do never be irritated when it doesn't be right at the first proof.
Do you have a pair of centers? One for the head stock and one for the tailstock? If you have place a six inch,(150mm), rule between the two with a light pressure. Looking at the rule and how it lies will tell you if alignment is out and in what plane.
Rough set/align and then chuck up a bit of scrap. Center drill the end and turn the outside round for about an inch. Part-off a bit about 1/2" long. file/stone off any pip. place parted off piece back in place where it came from and bring up center in tailstock to hold firm.
Rotate chuck while holding parted off piece staytionary with thumb and forefinger. You will be able to feel any mis-alignment very easily between the two faces,(radial displacement).
Short of having test bars and quality D.T.I.'s this is the easiest method I know. Note most tailstaocks are not true in the verticle plane from the factory.
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