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Tail Stock Alignment

Discussion in 'QUESTIONS & ANSWERS (Get Help Fast Here!)' started by petertha, Dec 26, 2016.

  1. petertha

    petertha Canada H-M Supporter - Premium Content H-M Supporter-Premium

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    I had to use a half ground dead center today that I haven't brought used that much. The part I was machining was simple shaft ~4" long, held in pretty accurate 3J chuck & center drilled for tailstock dead center. I spotted a taper on first measurements about 0.003" larger diameter on headstock side vs. tailstock across the 4". This taper remained about the same as I turned down the diameter. Not happy about this, but I finished off the part just correcting diameter with a file on final finishing. I figured maybe this center was wonky because normally I use live center & did not recall anywhere near that much taper before.

    So lathe cleaned off I chucked a DTI in 3J & measured ID of my MT3 quill by rotating chuck. I get: TOP=0.000", NEAR = -0.0055" BOT = 0.000 FAR =+0.0050". I did this in a few positions down the inside of the MT taper, always the same. I got thinking maybe my MT bore is elliptic but that is way too much & lathe never abused. I inserted dead center into MT socket & measured around the point section & also back on the full circular section just outside the quill lap. Same readings.

    Now it may well be that the chuck jaws are gripping the DTI stem off a thou or 2 so zeroing DTI with the dial facing up initially (what I call TOP) may influence clock relative readings, but what explains this measurement mapping & the taper cutting I'm seeing? I know I can screw the tailstock in/out laterally to adjust taper, but shouldn't I be seeing some hint of this on the readings corresponding to the cut taper? I can repeat this with a 5C collet & hold the circular DTI stem in that for better concentricity than the chuck. But I figure once its rotating, it should all be relative about headstock axis, no?
     
  2. RJSakowski

    RJSakowski H-M Supporter - Premium Content H-M Supporter-Premium

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    It sounds like you just have to move your tailstock over by bout .005". Vertically you are OK and your horizontal readings are equal but opposite which is good. Your method of measurement is indeed true to the spindle axis. The fact that you measure a .005" offset with the DTI but only see .003" taper in turning probably is indicating some twist in your bed. Turning the shaft is essentially the two collar test, as applied to use of the tailstock center and is a combination of alignment of the bed ways with the spindle axis and tailstock alignment.

    If you aligned the tailstock using the two collar test or Rollie's Dad's Method, you would automatically correct for both and you should turn a uniform diameter.
     
  3. 4gsr

    4gsr Global Moderator Staff Member H-M Supporter-Premium

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    RJ, it's reading an "egged" shaped diameter. That was my first impression too. Had to re-read his post.

    Peter,

    Scan over the OD of the tailstock spindle and see if you get the same readings. If so, then lets look at the headstock of your lathe.

    Ken
     
  4. petertha

    petertha Canada H-M Supporter - Premium Content H-M Supporter-Premium

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    Well it was an eventful & educational day. I'd even call it mostly successful.

    First off the tailstock. Not sure if addressing that was the proper starting point or root of the problem but I thought maybe easier to rectify. I had to sit down with my DTI, pencil & paper & figure out what deflection direction meant what. I'm pretty sure I befuddled myself by measuring OD vs ID of the quill & misinterpreting direction before. This time I marked quadrant points with a felt pen so the DTI ball would always land on the same spot. I broke the problem into 2 directional issues kind of like a 4-jaw chuck.

    First was vertical. I zeroed the DTI at TOP (12-oclock), then went round 180-deg & measured bottom (6-oclock). I helped to use a small mirror..which of course is kind of looking at things bass-akwards so you have to pay attention to dial direction. I did the quill OD, then ID & got prefect repeat every time. They are concentric. The tailstock barrel sits 0.002" high of lathe rotation axis. Tried this at different positions, barrel extensions, various clamping, always the same. I hear that high is normal & not a lot I can do anyway.

    Next was lateral in & out 3-oclock & 9-oclock, same method. Doesn't matter which position gets zeroed first but it made it simpler on my simple brain to note which side the tailstock was sitting. On my lathe I unscrew 2 set screws on end of tailstock (where hex wrenches are located) which I think clamp against the gib. Then unscrew the 2 main clamping screws (yellow arrows). With everything loose it was a simple matter of bumping the upper body until I got same DTI reading side to side, then tighten up arrow screws. Now the new learning bit,. Good thing I left the DTI in. Tightening the gib set screws can easily move the setting off several thou even with the main screws set. I'll have to look at the manual to see what this is about. So I kind of snugged alternatively but always watching to preserve my zero DTI reading. Now with everything is tight & accurate &bang on. The alignment graduation sticker cant be trusted, no shock there.
     

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  5. petertha

    petertha Canada H-M Supporter - Premium Content H-M Supporter-Premium

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    Now the tailstock situation improved & moved out of position for now, I chucked a poorly chosen chunk of CRS (no tailstock centering) & started down the path of: skim cut, measure diameter difference between head/tail stock side & shim adjust the appropriate lathe foot accordingly. I'm within 0.001" diameter on ~5" length. But I think I'm chasing my tail now so pausing to ask some more questions.

    It may well be the crappy steel quality of bar I chose. I blued it & took a spring pass at same depth but different traverse gear, but no real amount of excess material came off. The measurement change seemed rather muted, not like 1 leg turn = 0.0005" correction progressively towards some zero convergence. Maybe my stand is twisting but its not getting applied, or to the same degree, in the lathe bed itself? I can jack the feet up/down independently, no issue there. Its 2" square tubing 0.125 wall. You can see the lathe lugs are bolted to a cross member of the stand, but at a shorter lateral spacing. ie. the stand feet are spaced wider than the lugs. Do you think jacking the padded feet still is correctly applying corrective twist to the lathe bed in a consistent predictable manner? Then I did another cut & suddenly got same 0.001" deviation except this time it flipped direction & opposite end of bar was larger. wtf???? Are you supposed to adjust & then wait for a settling period?
     

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  6. British Steel

    British Steel United Kingdom Active User Active Member

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    Hi Peter, yes a settling time is a good idea, then rinse n repeat! Quality lathe makers used to 'season' castings for a year or more, rough machine and leave for stresses to work out before finish machining n grinding, adjustments for bed twist can take a day or two to settle, depending on the heft of the castings ( heavier take longer) - I leave a couple of days between adjustments, 2 tons of iron takes a while to relax!

    Dave H. (the other one)
     
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  7. Tozguy

    Tozguy Active User H-M Supporter-Premium

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    Peter, which end was larger when you first found the .001'' difference over 5''?
    I would make sure that the cutting tool was super sharp, had sufficient relief angles, and was perfectly on centre for this test. Even at that and with no twist in the ways, I would expect the free end to be slightly larger due to deflection.

    Ideally, the workpiece should be turned slightly smaller in the middle section so that you only have two hubs to cut for the final pass. Bear in mind that removing .001'' creates very little chips so if there are any chips at all do another spring pass.

    Padded feet, flex in the stand and stiffness of the lathe will tend to 'mute' the impact of adjusting the feet.
     
    Last edited: Dec 28, 2016
  8. petertha

    petertha Canada H-M Supporter - Premium Content H-M Supporter-Premium

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    Tozguy, I'm reducing diameter by 0.005" each test pass (0.0025" DOC) & locking the carriage Y-axis before traverse each time. For the most part my headstock diameter was larger than my tailstock diameter so my interpretation was to continue tweaking. Last measurement HS=1.0410", TS = 1.0420", so 0.001" larger on end. So my reasoning now: if its deflecting a bit on the end because its unsupported (steel is held cantilever in chuck, no tailstock center engaged) then maybe I'm pretty close to true parallel? I really want to check the bed with a good level now (sourcing). I feel like the tailstock problem was the overriding issue.

    I'm going to let it rest as-is & repeat this test with a chunk of 1.25" 6061. I have some sharp inserts that impart very little cutting load & leave much better finish. The cold roll steel was a quick grab thing & probably a poor choice. It took a couple cuts before I even got stable readings which I attribute to the skin & I'm always leery about stress relieving.

    So the dumbbell test bar shape with reduced diameter in the middle - I just assumed that was a time saving thing so you are not cutting continuously from end to end. Is that the case or maybe I misunderstood? My logic was cutting the whole section takes a bit more time but now I can mic along the way & see if there is any funny business going on like a bell shape or whatever.
     
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  9. RJSakowski

    RJSakowski H-M Supporter - Premium Content H-M Supporter-Premium

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    Peter, It is my impression that you aligned the tailstock by mounting a test indicator in the headstock and rotating the spindle to check the runout. This is a true indication of the alignment of the tailstock spindle for that particular tailstock position, quill extension, and measurement datum runout. Changing any of those could change the alignment.

    Additionally, if you have a twist in the ways or headstock misalignment, these do not enter into the equation. Consequently, you can have a well aligned tailstock but still turn a taper when turning between centers

    For taperless turning, I would mount a cylindrical test bar between centers and measure the position in the x direction with a test or dial indicator near the headstock center and the tailstock center. The position is measured relative to the cross slide/compound position so you don't want to change them while making the measurements. If the test bar is round, the measured position of the axial center of the test bar at that point on the bar is average of the minimum and maximum readings (ref. Rollie's Dad's Method). Without changing the cross slide or compound, move to the second position and remeasure. If the two averages are the same, you should be able turn a taperless bar.

    If you use a test bar such as this, the maximum and minimum readings should be identical as the test bar is theoretically straight and the centers are located at the true center of the test bar.

    http://edgetechnologyproducts.com/tailstock-alignment-bar/?utm_medium=googleshopping&utm_source=bc

    Note that this measurement uses the position of the cross slide relative to the spindle axis so, although the tailstock alignment is true for that particular setup, it takes into account all of the factors which affect that alignment. If there are misalignments in one or more of the contributing factors, any change can affect that. To get around that, I would insert the work piece and turn collars to the same diameter, as measured with a micrometer. near the centers, using the cross feed if necessary. I would then go through the measurement procedure described above to adjust the tailstock for the same averages. Since your workpiece is already in position, none of the setup will change and you should be good to go.

    Note 1. This is a procedure to quickly align the lathe for turning a taperless bar. It is not a substitute for a full lathe alignment. The advantage of this method is that it eliminates the "turn" from the "turn, measure, adjust" sequence.

    Note 2. If you read the background of Rollie's Dad's Method, you will see that the only requirement is that the test bar be round. You can actually measure two different diameters as long as you include the diameter of measurement point in the equation. With this, you don't even have to adjust the crossfeed to turn equal diameters when making the second cut on your workpiece.

    Note 3. While this measurement procedure will theoretically turn a uniform diameter, it does not account for tool deflection or workpiece flexing, as mentioned above.
     
  10. RJSakowski

    RJSakowski H-M Supporter - Premium Content H-M Supporter-Premium

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    I think the dumbbell shape is so you don't put necessary wear on your cutting tool as you move from one point to the next. Using this method, you definitely don't want to change any settings on the crossfeed/compound.
     
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  11. petertha

    petertha Canada H-M Supporter - Premium Content H-M Supporter-Premium

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    Thanks for you comments RJ. Makes total sense to me. That Edge bar looks very useful, thanks for link. Setting up my DTI wasn't too difficult & I learned some new things I probably should have paid better attention to. If I set the DTI ball to a slightly different position within quill ID, it was usually pretty close but could deviate 0.0005" depending on the wind :) I was similarly concerned about repeatability especially if the tailstock was further away & my Nooga arm was hanging way out, maybe influenced by gravity? The nice thing about that bar method is it uses centers which are more engaged & averaging within the socket & also over longer distance so less prone to picking up any local deviations
     
  12. Uglydog

    Uglydog United States Active User H-M Supporter-Premium

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    I've heard that it was historically common to bury them, and that more recently it has been a practice to wrap them in black plastic and set them in a southern exposure. It's difficult for me to discern best practice from folly. Regardless, metal moves, slowly... except when it is machined, then it moves fast.
    Daryl
    MN
     
  13. petertha

    petertha Canada H-M Supporter - Premium Content H-M Supporter-Premium

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    I left the slug in the chuck overnight & ran 4 measurements on each side & averaged. Its now 0.0013" larger on headstock side than tailstock. I swear it has a beating heart. But I also used a different micrometer this time so who knows.

    I did another test. I placed DTI on bar end at outboard ~5" mark, shoe laced my fishing scale around the end & pulled on it. At something less than 10 lb it deflected 0.001" The question is, how push tool pressure would my bar have seen while cutting? I'm anxiously awaiting arrival of my new measurement goodies, maybe they will shed additional light on the issue.
     
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  14. Tozguy

    Tozguy Active User H-M Supporter-Premium

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    As you know, it only takes a deflection of .0005'' to get .001'' on the diameter. The two hub turning test (with free end unsupported) is better at detecting twist in the ways than by using a level.
    Repeating the test with some 6061 is a good idea.

    RJ has already answered the last question.

    What is the tailstock problem again? The TS is adjustable as you show above. It is common to move the TS to deliberately turn tapers between centers. The TS has to be adjusted back into alignment to turn cylindrical between centers. Must not have twist in the ways to be able to align TS properly.
     
  15. petertha

    petertha Canada H-M Supporter - Premium Content H-M Supporter-Premium

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    The problem was lack of good procedure on my part. To adjust into position:
    - tailstock is locked down on lathe bed
    - I unscrewed the (orange) set screws that act against what looks like a gib strip on tailstock end
    - I unscrewed the (yellow) set screws that look like they lock on either side of that extended boss in the base
    - lightly tap the tailstock unit into position so tailstock quill is coincident with spindle plane (yes same mode as offsetting tailstock when consciously setting up for taper turning)
    - tighten yellow screws so tailstock aligned
    - and now last step. I just assumed tighten orange screws to lock down position. However I still had the DTI hooked up & noticed if I turn one screw & not the other. I can actually tweak the tailstock out of position. Almost like in a rotation axis viewed from the top. So I alternated tightening them back & forth watching the dial to stay at zero. I'm still not sure if these end screws are meant to be a fine tuning adjustment. Or maybe its a bit of unwanted junk movement like when I tighten my cross carriage thumbscrews against its gib the DRO shows a smidge of movement. (Actually I cured that issue with a bearing ball & a little foot cut at same angle as dovetail, but this is what I'm wondering).
     

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  16. petertha

    petertha Canada H-M Supporter - Premium Content H-M Supporter-Premium

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    Interesting. I was reading this old Southbend lathe installation & levelling guide. They show a screw adjuster located above the tailstock base hold down bolt for adjusting the bed. I kind of wish my Taiwan lathe cloned that feature, maybe would take the stand out of the levelling equation?
     

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  17. petertha

    petertha Canada H-M Supporter - Premium Content H-M Supporter-Premium

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    Not sure why I didn't stumble on an informative 2 part YouTube video earlier, but it covers lots of points discussed: Tom Lipton (Oxtool) Leveling and Setup of the metalworking lathe P1 & P2. After his lathe levelling iterations kind of got to the end of the trail, he ended up taking his the last thou taper out by headstock adjustment. I'm not there yet but starting to wonder out loud if that's where I might end up. Excerpts from my <cough> extensive manual in that regard. I'll have to snoop around corners of the lathe but this is what I'm thinking. Now whether its meant to be tweaked or that's where they wrenched it down at the factory & called it 'within spec' is another matter.
     

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  18. petertha

    petertha Canada H-M Supporter - Premium Content H-M Supporter-Premium

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    OK, I had a productive day. This time I chucked a ~7" bar of 1.375" diameter 6061 aluminum because it was handy. I didn't do the dumbbell relief cut but took a few skim passes with a really good insert. I took 3 headstock/tailstock measurements at 3 different clock positions, average them & got 0.0031" difference over 6.5" length. Tailstock dia > headstock dia. So same direction as my steel bar. A larger difference because it was over longer length & I wasn't to confident about the CRS bar anyway. So assuming the lathe is level (not 100% sure there yet but will have to revisit that when I get my good level) this would infer the headstock axis is pointing to the rear of the lathe, tailstock side. Or counter-clockwise if viewed from the top.

    I sucked up my kahoonies & loosened the 4 bolts I was 99% sure were holding the headstock in position. Well... 3 bolts. Dang. The one closest to operator, inside the pulley cover, behind a gear, up in the attic, behind a casting boss, not quite reachable with any hex wrench known, or modifiable by man... I could not get a hex wrench engaged with limited rotation to loosen properly. I maybe got a start on it with the ball end of hex but was concerned I might gal the hex socket so decided to leave it for now. I did remove the gear to get at it BTW, but I think even more extensive gear bracket disassembly would be required. Why not use a not a hex head bolt that would be so easy to reach with ordinary wrench he asks himself?

    Anyway I set up 2 dial indicators on either end or bar so I could monitor lateral headstock rotation movement. I then turned in the jack screw 1/ turn or so on rear of lathe & saw the head move 0.0025 on TS side & 0.0005" on HS side. Shy of target 0.003" but thought I'd start there. The remaining hold-down bolt I couldn't loosen allowed the slight rotation movement & that's all I was hoping for. Clamped the bolts down again, re-installed gear, let the lathe warm up a bit, took another skim pass. This time my differences were 0.0008", 0.0007", 0.0009" TS>HS so call it 0.0008" average over 6.5". This definitely did some good & I suspect my issue all along. Going to leave it be for now & then start at the beginning again when level arrives.
     

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  19. RJSakowski

    RJSakowski H-M Supporter - Premium Content H-M Supporter-Premium

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    Now that you have rotated your headstock, you should check if you are cutting a flat face. You could mount a face plate and mount a dial indicator on the cross feed. Measure at a point near the front and mark the spot. Rotate the spindle and move the cross feed to the rear to intersect the spot again. Your indicator should read the same (some folks set their lathes up to cut a slight concave face).
     
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  20. petertha

    petertha Canada H-M Supporter - Premium Content H-M Supporter-Premium

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    You are one step ahead of me RJ. I JUST finished skimming a 10" faceplate a few weeks back on the old headstock setting. Once I'm happy with the lathe setup, yes will have to check the plate & likely give it a light re-surface. It wasn't an onerous job, but the cast iron powder seems to get everywhere. Going to lay down some lightly oiled paper towels or something.

    So my story is still a bit open ended until my accurate level arrives to validate lathe twist status (the leg jacking rigmarole). But is the proper sequence like what Tom Lipton shows:
    - adjust lathe level (twist)... but within reasonable limits
    - if still cutting taper, zero lathe twist & proceed to headstock

    Reason I ask is I got thinking about this bed twist issue, if done in isolation as a cure. If the dumbbell test cutting is always confined to relatively short length of the test bar, say 10". And you kept twisting the bed until taper was removed over that 10", couldn't you end up with a piece of licorice extrapolating the twist angle out the remaining 30" of bed or whatever?
     
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  21. RJSakowski

    RJSakowski H-M Supporter - Premium Content H-M Supporter-Premium

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    Like you, I am awaiting the acquisition of a machinists level to refine my alignment.

    Since I have no way, aside from headstock rotation, of aligning cross feed ways to the spindle axis, I will probably do that second, after leveling. My Grizzly 602 lathe has only two mounting bolts, under the spindle axis at the headstock and tailstock. It is my belief that when I installed the lathe, I pulled the lathe to my home-built table and distorted the casting.

    Noticing a taper similar to what you observed, I rotated the headstock which eliminated the taper but now I cut a domed face. The correction that I made for taper is virtually the same as the misalignment that I am observing in the cross feed. In other words, I have used two wrongs to make it right.

    My latest thoughts on alignment are that I should loosen the two mounting bolts to relieve stresses. My first adjustment would be for headstock rotation, as indicated by flatness of a machined face. The reasoning for this is the carriage is not moving along the ways so the effects of any twist would be minimal. Once the spindle axis is perpendicular to the cross feed ways, I would level the lathe bench, using the adjustments on bench feet, and then the lathe, using shims. Finally, I would check for taper, using Rollie's Dad's method and adjust shims under the headstock and or tailstock. The shims under the headstock end would be equal front to back and used to correct a vertical tilt in the spindle axis. Shims under the tailstock end would be to correct for twist.

    There is also possibly a horizontal and/or vertical misalignment of the tailstock quill to the spindle axis which could be a combination of radial and angular misalignment. I would check that by mounting a test bar between centers and using the RDM method again. Checking with the quill retracted and the quill extended should pick up any angular alignment issues.
     
  22. petertha

    petertha Canada H-M Supporter - Premium Content H-M Supporter-Premium

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    Coincidentally Keith Fenner just posted a YouTube video on very similar headstock re-adjustment procedure I went through (notwithstanding his unfortunate oil drain PITA). YouTube title is: Let's Look Under The Old Girls Apron Part Eleven. I think that MT5 straight bar is the cats meow.
     

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