My tailstock is off

[zeeprogrammer]

After a bit of a hiatus...I started machining again and remembered an issue I'd noticed some time ago.

With a center drill in the tail stock...when I bring it up to the part, the point is off center and when it touches the part it flexes slightly to get to center.

For the 1st picture, without the machine running, I pushed the center drill into the part. You can see the mark is slightly off center.

I didn't want to take my chuck off and put a dead center in the headstock so I made a pointy thing. Then put a dead center in the tailstock.

The 2nd picture, taken above, shows the mismatch.
The 3rd picture, taken from the front appears to look okay (allowing for parallax and shaky hands).

1st question is...shouldn't this be addressed? It's wrong, right?
2nd question is...how to address it. The 4th picture shows my tailstock. Note the large bolt in the base. There's one on the other side too.
I don't know anything about adjusting a tailstock.
Is it a matter of loosening one and tightening the other to center the tailstock (much like a 4-jaw chuck)?

I also don't know, as the ram is moved in and out whether everything moves in-line with the headstock or at a slight angle (which would mean the error increases/decreases as the ram is moved.

3rd (and last) question is...how does one go about measuring the accuracy of the tailstock and ram movement?

Thanks.

[Jo]

Assuming the height is correct it is an easy fix Zee

On your tailstock at the bottom you will see two grub screws at the front and the back these can be loosened off and tightened up to offset the tailstock. Clearly when they put your lathe together they did not get the adjustment right  Best set it up using a dial gauge around the tailstock barrel and leave it locked.

3rd (and last) question is...how does one go about measuring the accuracy of the tailstock and ram movement?

Measure it using a dial gauge mounted on the saddle and move it along the tailstock barrel by moving the saddle

Jo

[michaelr]

Is it my eyes ? One chuck jaw sees to be not in contact with your dead center

Mike..

[zeeprogrammer]

Thanks Jo. I was worried about making things worse before confirming what I'd thought.

Mike...my homemade dead center came from scrap. Further in, all the jaws are making contact.
In effect, it's no different had I had it sticking out further (past the recommended length for turning that diameter).
True, more jaw would have made contact...but it was sufficient for this.

It wasn't done well...but I think well enough to show the problem.

[petertha]

When you turn a center point in-situ held in the chuck, then yes, you have made yourself a pretty reliable center. This occurs because its rotating of course. And this method is to make reliable temporary centers when its known or assumed that the chuck may be out. So this method could be used as rough indicator brought up against a tail stock center like you show. But I wouldn't tune my tail stock to this beyond a rough guess to get in the ballpark.

A better method is simply clamp a dial indicator assembly to the chuck, lathe backplate, anywhere convenient on the rotating headstock assembly. Then sweep the dial around the outer perimeter of the MT center. It doesn't have to be on the tapered point part, in fact easier & more accurate on the OD portion extending from TS barrel. Now you have good information. You can determine in/out runout and also up/down runout. Make your TS adjustment with the set screw, but leave your DTI in place as they can be a bit fiddly (think 4 jaw chuck tensioning method). There isn't a lot you can do with vertical deviation unless you want to scrape. It is not uncommon to have the center a bit high, say 0.002". the good news is it doesn't matter as much.

Now you can even pull the TS dead center & eliminate the middle man so to speak & DTI around the inside of the barrel. Just lock everything down so that its reading at the same taper ID circle. Measuring deviation of extending the barrel could be done along these same measurement lines on barrel OD. But get it centered first & again. lock the TS casting.

You will find properly centered TS is well worth the effort. It might help explain a step change improvement in drilling, spotting & eliminating tapers of between center turning.

Last point. This method in theory aligns the axis of your headstock & tailstock. It does nothing for a chuck that has 0.005" runout which will still clamp work this amount 'off center'. There are also other fundamental lathe adjustments that may supersede this (top view headstock alignment, lathe twist...) but save that for another day. LOL

[petertha]

BTW, lathes vary in how their TS are adjusted so consult your manual.

On my Taiwan 14x40, I first loosen the 2 grub screws which act against the TS dovetail gib. Then the TS is displaced into position with a larger screw in the base casting facing the operator (unfortunately not shown). Now with zero DTI established (headstock & tail stock are co-axial) then the 2 screws are re-set in this position as shown in pic of 2 hex wrenches. But what I found, because I had my DTI in position the whole time, I could actually make the TS drift about 0.004" either way off the zero position depending on how I tightened the screws. If you gronk one down & then the other, its almost a guarantee it will deviate. The better way is to alternately snug them & watch the needle maintaining zero.

[zeeprogrammer]

Thanks very much petertha. 

I lost sleep last night thinking about this. Some of you may recall the #7 twin cylinder I made a month or so ago and the trouble I had with one of the cylinders and piston rod.

After drilling, using the tailstock, the cylinder was bored using the lathe carriage.
Then the cylinder cover hole, through which the piston rod goes through, was done using the tailstock.
I had wondered how the hole in the cylinder cover would be concentric with the cylinder bore.

[Jasonb]

Zee you will have to slacken the clamp that holds the tailstock to the bed when you make the adjustment using the two screws Jo described then tighten the lever to check with DTI

[zeeprogrammer]

Zee you will have to slacken the clamp that holds the tailstock to the bed when you make the adjustment using the two screws Jo described then tighten the lever to check with DTI

 

[Art K]

Zee,
I just thought I'd chime in here. Dito on what petertha said. I have an Enco 12X36 gear head lathe at home and a nearly identical one (more abused) at work. The one at work runs out about .012 on one jaw. But I made the valves for my Upshur single on this. These have a similar set up as yours with the adjustment screws, one on each side. As far as I know there is no lock down screw on mine. On the valve stems I had it adjusted to .0002" end for end, and had to file and polish down the center of the stem to match. AND no kidding trying to adjust the centers that close is quite fiddly. If you do as suggested and indicate it in it will stay close enough for most work. But it will change slightly every time you move the TS and lock it down. If you ever do a run of a lot of parts that are the same It's best to do them all in the same set up and not move the TS.
Art

[zeeprogrammer]

If you do as suggested and indicate it in it will stay close enough for most work. But it will change slightly every time you move the TS and lock it down. If you ever do a run of a lot of parts that are the same It's best to do them all in the same set up and not move the TS.

Yes!  I've noticed that.

[Tennessee Whiskey]

Zee, there are numerous ways to align a tailstock. I tend to lean towards taking a 12” piece of 1” or larger stock and situate it between a turned in situ center in the headstock end and a center in the tailstock. Take a  .005” ( or whatever it takes to clean it up) cut down the length. Mic each end. Move tailstock as described half the distance of the difference and try again: until you achieve dead nuts readings on both ends. My simplistic way of doing it 

Cletus

[petertha]

There is a Gucci do-dad you can buy from Edge Tools that has 2 identically ground collars on either end & also 60-deg center drills. The idea is you put the bar between centers, mount a DTI to the carriage, zero register DTI to head stock collar, traverse & read measurement on the tail stock side. Move the TS in or out to zero position. Really, you could make one of these by accurately turning down say a 1" wide band on either end of bar stock to any arbitrary diameter, as long as they are the same. If you keep stick-out from chuck low during machining, they are bound to be accurate. The middle bar section doesn't matter at all. You aren't measuring there & it potentially introduces other deviations like bowing without a steady. The longer the bar, the more axial the centers will be on even a 0.001" DTI reading. Or if for some reason you are doubting the re-positioning of the TS at different distances from the HS, you could make a few different lengths. Although I'm trying to think of a good reason why the TS should be drifting along the bed to begin with if the ways are accurate & TS slides along a Vee register at least one hopefully. If the ways are out, then so is your carriage trajectory.

[petertha]

There is another more insidious alignment issue that actually should be established prior to any TS checking. And that is the alignment of the head stock itself. If that is out (meaning HS cocked at an angle looking down from the top) then the lathe will cut a taper which has nothing to do with the tail stock. Aligning the centers of HS & TS centers is secondary. If your particular lathe HS is fixed, then sorry that is the end of the trail. My lathe has the typical hold-down bolts & jack screws to tweak it into position. Warning! you breath on these & they move so proceed with caution. The easiest way I know to check is buy what has to be one of the best bargains, a straight test bar with MT taper on one end. I got mine from an Ebay seller, made in India but remarkably accurate which was a shock. Plop the MT end in your HS & socket DTI down the length with mag stand on carriage. If its out, you know you have to deal with this issue first. You can evaluate in/out & also any vertical pitch. My HS is MT5 so I use an MT5/MT3 socket adapter which came with the lathe. The nice thing I can use the same test bar in TS which effectively exaggerates the TS barrel where you can also measure relative to ways.

This topic often gets contorted into 'lathe levelling'. And by that, they really mean lathe bed twist. But even with a 100% level & untwisted lathe, if the HS is pointing in or out, it will cut a taper & TS alignment will appear 'variable' at distance & basically never be axial by definition.

[john mills]

inspect the inside of the taper make sure it is clean .also take the tail stoke of the bed and check that there is no dirt or swaf underneath it is easy to pick up some dirt and that will put every thing out .clean the taper inside any dirt   swaf can stick and cause problems always keep cleaning tapers.

[steamer]

Head stock should point up and out 0.0005/12"   This allows for cutting pressure and assures it will cut concave and not convex.

[steamer]

See reply #354

http://www.modelenginemaker.com/index.php/topic,369.350.html

I have pictures of the procedure.

Dave

[zeeprogrammer]

Head stock should point up and out 0.0005/12"   This allows for cutting pressure and assures it will cut concave and not convex.

That confuses me. I hadn't seen a spec like that.

1) Is Rollie's Dad's Method affected by that?
2) At the distances I usually cut (1" to 4") does this really have that much affect?
3) I don't understand concave versus straight. And is this when turning, facing, or both?

Thanks.

[steamer]

Head stock should point up and out 0.0005/12"   This allows for cutting pressure and assures it will cut concave and not convex.

That confuses me. I hadn't seen a spec like that.

1) Is Rollie's Dad's Method affected by that?
2) At the distances I usually cut (1" to 4") does this really have that much affect?
3) I don't understand concave versus straight. And is this when turning, facing, or both?

Thanks.

Is rollies Dad's method affected.     NO.  It's unlikely you will even see it while performing Rollies Dad's method......Rollie is a great guy!   You should meet him sometime.

At the 1-4" distances it shouldn't unless it's really out.     The spindle nose should point up and towards you  .0005" at 12 inches from the spindle nose.   It's not a lot

If it cuts convex, during a facing cut, the center of the part will be longer than the OD, and the part will not sit flat on a flat surface.  If it cuts perfectly flat or concave, it will set on the face or the perimeter of the part.    Again...  This dimension is specified to allow for deflection of the lathe subjected to cutting forces during facing primarily.


I can sketch it and post if you want me to.


Dave

[petertha]

I'd like to see your sketches Steamer, I'm interested in this stuff.

I've read through RDM, both in what I think is the official procedure link below and on other forums.
http://manuals.chudov.com/Rollies-Dads-Method-of-Lathe-Alignment.pdf

I guess I don't quite understand the nuances of RDM. When a headstock axis deviation is measured using RDM (notwithstanding all the shaft averaging business which I still can't quite get my head around), at the end of it all the recommended 'fix' is to start 'leveling' the lathe. Which is another way of saying introducing or removing lathe bed twist to compensate. But I can envision a 100% planar lathe bed resting on a 1-degree slope without introducing taper cutting issues. Providing the lathe bed is designed to be sufficiently rigid under its own weight which it should be. How is the lathe being adversely affected?

But as I mentioned in an earlier post, if your headstock is adjustable in the yaw plane viewed from top, which many machines are, I would think all levelling bets are off & this deviation trumps shimming the lathe feet. Maybe RDM was documented in a time or specifically for lathes that have the spindle axis cast in place (meaning there is no HS adjustability). This I can see as a correction of last resort. But for 2-part headstock/bed lathes, I would think this would be the focal point especially if they were ever moved or never adjusted over time. Think about it exaggerated: if my lathe was 100% level & 100% untwisted, then I loosened the HS bolts & cocked the spindle axis 10-deg in our out relative to lathe bed, how much shimming & jacking of the feet would have to be done to twist the lathe bed to compensate? Answer: a lot. Unless I'm missing something fundamental, its attempting to solve the problem with the wrong lever.

Back to convex/concave I think this might be related to facing cuts on the end of stock? The way I envision it is:
- if extended HS axis is pointing to front of lathe then a facing cross cut will yield a shallow inward concave cone. In non-TS supported longitudinal cutting, the carriage travel will cut a taper where the TS side diameter is smaller than the HS side, no different that TS supported offset taper cutting method.
- if extended HS axis is pointing to rear of lathe then facing cross cut will yield a shallow outward protruding convex cone. Longitude cutting will yield taper in opposite of above, TS diameter larger than HS diameter.

Of course cutting forces & material & cantilevered vs. supported stock can mask what are probably tiny deviations.

[steamer]

I'd like to see your sketches Steamer, I'm interested in this stuff.

I've read through RDM, both in what I think is the official procedure link below and on other forums.
http://manuals.chudov.com/Rollies-Dads-Method-of-Lathe-Alignment.pdf

I guess I don't quite understand the nuances of RDM. When a headstock axis deviation is measured using RDM (notwithstanding all the shaft averaging business which I still can't quite get my head around), at the end of it all the recommended 'fix' is to start 'leveling' the lathe. Which is another way of saying introducing or removing lathe bed twist to compensate. But I can envision a 100% planar lathe bed resting on a 1-degree slope without introducing taper cutting issues. Providing the lathe bed is designed to be sufficiently rigid under its own weight which it should be. How is the lathe being adversely affected?

But as I mentioned in an earlier post, if your headstock is adjustable in the yaw plane viewed from top, which many machines are, I would think all levelling bets are off & this deviation trumps shimming the lathe feet. Maybe RDM was documented in a time or specifically for lathes that have the spindle axis cast in place (meaning there is no HS adjustability). This I can see as a correction of last resort. But for 2-part headstock/bed lathes, I would think this would be the focal point especially if they were ever moved or never adjusted over time. Think about it exaggerated: if my lathe was 100% level & 100% untwisted, then I loosened the HS bolts & cocked the spindle axis 10-deg in our out relative to lathe bed, how much shimming & jacking of the feet would have to be done to twist the lathe bed to compensate? Answer: a lot. Unless I'm missing something fundamental, its attempting to solve the problem with the wrong lever.

Back to convex/concave I think this might be related to facing cuts on the end of stock? The way I envision it is:
- if extended HS axis is pointing to front of lathe then a facing cross cut will yield a shallow inward concave cone. In non-TS supported longitudinal cutting, the carriage travel will cut a taper where the TS side diameter is smaller than the HS side, no different that TS supported offset taper cutting method.
- if extended HS axis is pointing to rear of lathe then facing cross cut will yield a shallow outward protruding convex cone. Longitude cutting will yield taper in opposite of above, TS diameter larger than HS diameter.

Of course cutting forces & material & cantilevered vs. supported stock can mask what are probably tiny deviations.

Working on loading a sketch

RDM will minimize your errors....all the errors.    Most beds are not perfect, and RDM will just show the errors but won't tell you where they come from.  If you have a perfect bed, dead level, then that shouldn't show up at all...but few beds are perfect.


As to the result of having the TS engaged or not with different HS alignment conditions....In general I agree...but the work piece will influence the out come in non-intuitive ways depending on how stiff it is, how it's mounted to the headstock  ( chuck, what kind of chuck, condition of the chuck, just a dead center in the spindle....ect)

My numbers come from the SB test sheets, and "Machine Tool Reconditioning"   
They are based on a test bar mounted in the spindle nose.

[petertha]

Here is my attempt at putting picture to (my) words. Click PT headstock alignment PDF, its kind of hiding right on top of pics. At this level it has nothing to do with chucks, test bars, cutting pressures or tail stock support interaction... Just focusing on the headstock alignment axis relative to the bed way axis in planar 2D. And the usual caveats; bed ways are straight, carriage travels along them straight & cross feed travels perpendicular to straight.

My 14x40 lathe pics. Kind of hard to see, but these are the 4 HS hold-down bolts. The shimming grub screws are deeper down the rabbit hole.

[steamer]

The Southbend doesn't have that adjustment.   It has a flat and V way, so once the HS is down....it's not moving.    The only way to move it is to shim it,,,


Or

Scrape it    Which I did.

Dave