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Thread: Help me find and fix a lathe problem

  1. #1
    Join Date
    Sep 2013
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    Help me find and fix a lathe problem

    My lathe, of late, is driving me crazy. I spent several months turning big heavy green bowls, and have recently gotten back to between-centers work and boxes and such. I think I've either knocked something out of whack or hosed my bearings. (They have never been replaced)

    The lathe is a Conover from 1990.

    The symptoms are constant vibration, increased chatter, and inability to re-mount anything and have it run true. I use a dead center as a small ring drive (like what Oneway describes as a "safety drive") and on other lathes as recently as last week re-mounting is nearly flawless. It was very good on this lathe in the past, now I'm off center by 1-2 mm every time I put the piece back on. If I rotate the workpiece on the ring it goes off center.

    I measured runout on the spindle with a dial indicator. At the front end it is zero to my ability to measure. At the handwheel end of the headstock the spindle is eccentric by about 0.4 mm when rotating the spindle by hand. The points on two different centers describe a small circle as they rotate at speed.

    There is no perceptible motion in the headstock, other than the expected rotation. I can't move the spindle in any direction. It does make a new whirring noise under load when the bearings are loaded.

    Replacing the bearings is something of a project in this machine, so I don't want to overlook some other obvious problem/solution.

    The ultimate solution is arriving from Wisconsin in about 8 weeks , but I'll need this one to be in salable shape then, plus I was planning on making a run of pepper mills for Christmas gifts and I'll go crazy trying to do it with the lathe in its current condition.

    Anything else I should check or try?

    Pictures show how I measured-- I'm no machinist, so please tell me what I'm doing wrong!

    IMG_1610.jpgIMG_1609.jpg

  2. #2
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    It may be possible that the head stock and the tail stock are not perfectly aligned, thereby giving you a vibration as the piece oscillates at one end. Compared to both ends being aligned and in perfect synchronisation when things are correct.

    Your description sounds similar to what I experienced with quite an old lathe where the tail stock had slight sideways movement, which was almost negligible but noticeable. I would unlock the tail stock then push/hold it to one side as I locked it again. Then it ran almost perfectly and silently, once more.

    You may also have a dodgy bearing, going on what you are hearing. Bearings are usually not too hard to replace, but if you are moving the lathe on in 8 weeks..........................

    Mick.

  3. #3
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    The headstock vibrates pretty badly without anything attached to it. I will try resetting the headstock in position, if it were cockeyed relative to the tailstock that would certainly give me the remounting problems. I seat it firmly against the back rail by tapping in tapered shims.

  4. #4
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    Roger, also check your pulley in the headstock has not come loose and also inspect your drive belt incase it is coming apart.
    Rgds,
    Richard.

  5. #5
    Join Date
    Feb 2008
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    E TN, near Knoxville
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    If good points in good sockets describe a circle when turning by hand I suspect something is seriously wrong with the spindle or headstock. Could the spindle have been bent by some massive event? Can you get your indicator inside near the center, perhaps next to a pulley? (Might have to remove it from the headstock for a thorough check. Could the headstock casting be warped? Did turning spindles in the past work as expected?

    Seems to me if the bearings were at fault the whole thing would be noisy and sloppy.

    Are the #2MT sockets on both the headstock and tailstock good, clean, and with no internal burrs? I use a #2MT cleaner and have MT reamers in case of galling, dents, or burrs but I have fixed such with a round file. You can feel for roughness part of way the inside with a finger. You can check for play by mounting a good center in the tapered sockets and wiggling.

    As others said also check the headstock to tailstock alignment. Put points in both and slide the tailstock up next to the headstock point. If they are misaligned horizontally, adjust the height of one leg until the lathe bed twists enough to bring them together. At a demo Mark StLeger commented that the misalignment on the club lathe was giving him grief and a lot of vibration. I used the leg adjustment method to fix it in just a few seconds. Note that a lathe in perfect alignment can go wonky simply by moving it a few inches across the floor. Of course, if the problem is the spindle is not straight this won't fix anything.

    BTW, I turn a lot of spindles but rarely between centers. I mount one end in a chuck and use a tailstock live center on the other end if needed. Can you turn things as expected with the blank mounted in a chuck?

    JKJ

  6. #6
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    Vibration can also come from the motor. Drop off the belt and run it to see how the motor spins. Make sure any set screws are tight, and no keys are missing under the pulley on the headstock. With that wood bed, misalignment with the tailstock can also be a seasonal thing when the wood shrinks or twists in the drier winter air.

  7. #7
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    Resetting and carefully realigning the headstock has helped dramatically. I'm going to go back and try the leg adjustment trick to see of I can tweak it the final bit. I've also noticed that if I'm not careful the tailstock cants a bit as pressure is applied. The headstock must have gotten knocked cattywampus while working on those big bowls. It's not perfect, and the vibration and wobble in the hand wheel is still there, but now I can do what I want to do. Perhaps turning for a week on a big Oneway at Marc Adams school spoiled me and I'm only just noticing the vibration.

  8. #8
    If you have a sliding headstock, both it and the tailstock need to have the bottoms cleaned off once in a while. Loose screws on your chuck jaws can be a problem too, and some times they just seem to work themselves loose. Most other things have been covered here.

    I have found out the trick to leveling your lathe too, and it may take an attempt or three to get it perfect. 3 points make a plane/flat surface. So level up the lathe with 3 of the legs. Then get the 4th leg close. Put an unbalanced piece of wood on the lathe and turn at a speed that makes the lathe vibrate, but not shake violently. Tighten up that one leg a bit till the vibration stops. Go a hair past and slack it off again, and find the sweet spot. You may need to do it a couple of times. I also use a magic marker on the concrete floor so I know where the exact spot is because, especially if you turn a lot of bowls, the lathe still vibrates a tiny bit and it will move. This moving is also a result of torque...

    robo hippy

  9. #9
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    Quote Originally Posted by Reed Gray View Post
    If you have a sliding headstock, both it and the tailstock need to have the bottoms cleaned off once in a while. Loose screws on your chuck jaws can be a problem too, and some times they just seem to work themselves loose. Most other things have been covered here.

    I have found out the trick to leveling your lathe too, and it may take an attempt or three to get it perfect. 3 points make a plane/flat surface. So level up the lathe with 3 of the legs. Then get the 4th leg close. Put an unbalanced piece of wood on the lathe and turn at a speed that makes the lathe vibrate, but not shake violently. Tighten up that one leg a bit till the vibration stops. Go a hair past and slack it off again, and find the sweet spot. You may need to do it a couple of times. I also use a magic marker on the concrete floor so I know where the exact spot is because, especially if you turn a lot of bowls, the lathe still vibrates a tiny bit and it will move. This moving is also a result of torque...

    robo hippy
    Remember, on a Conover you are clamping the headstock and tailstock to a wood bed. Cleaning the bottom of those would not have the affect as it would on a steel bed. Vibration could easily compressed wood fiber and thrown off the alignment.

  10. #10
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    Quote Originally Posted by roger wiegand View Post
    Resetting and carefully realigning the headstock has helped dramatically. I'm going to go back and try the leg adjustment trick to see of I can tweak it the final bit. I've also noticed that if I'm not careful the tailstock cants a bit as pressure is applied. The headstock must have gotten knocked cattywampus while working on those big bowls. It's not perfect, and the vibration and wobble in the hand wheel is still there, but now I can do what I want to do. Perhaps turning for a week on a big Oneway at Marc Adams school spoiled me and I'm only just noticing the vibration.
    If the head and tailstocks are fastened to a wood surface as mentioned, the alignment needed might be quite different. I know nothing about that specific lathe (never saw one) but it makes me wonder if the wooden bed needs to be dressed or somehow improved before alignment.

    A new Oneway, Powermatic, or Robust might increase your quality of life! Life is short, play hard.

  11. #11
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    Wayland, MA
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    Judged with a good straightedge the ways are still flat. If I were keeping the lathe I'd probably try, as many used to do, brass or stainless inlay strips on the wear surfaces.

    Although the misalignment is much better, it's not yet good enough for what I'm trying to do right now. Perhaps I'll go back to bowls where it doesn't matter. I'll work on leveling now, though it sits solidly currently. I'm on an uneven wood plank barn floor, so that too is a challenge.

    My darling wife decided that she'd like to give me a nice present for my upcoming big-number-that-ends-in-a-0 birthday (not 50), so the AB will be arriving right after New Years. I haven't been so excited in years!

  12. #12
    Your wood barn floor is likely a contributor to the issues you are having. Only way to know for sure would be to move it to a concrete pad.

    robo hippy

  13. #13
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    Quote Originally Posted by Reed Gray View Post
    Your wood barn floor is likely a contributor to the issues you are having. Only way to know for sure would be to move it to a concrete pad.

    robo hippy
    Well that's a depressing thought. A new building isn't in the works. The floorboards are 3" thick sitting on 3x10 joists 12" OC spanning about 8 ft. (whoever built that floor had the "if it's worth doing it's worth overdoing" philosophy.) Nonetheless it will surely move more than concrete. I've thought about bedding a sheet of plywood in mortar on the floor to give me a flat, level surface for the new lathe. I suppose I could take that up a notch and pour a 3-4" slab on top of the wood. Either would be kind of ugly, so I'll probably see if I have a problem with the new lathe before doing that.

  14. #14
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    Quote Originally Posted by roger wiegand View Post
    ...The floorboards are 3" thick sitting on 3x10 joists 12" OC spanning about 8 ft. ...
    Wow, I suspect your floor would be fine for any lathe. And as long as the legs have adjusters the floor doesn't even have to be flat, although that would help if you had to move the lathe around a lot.

    JKJ

  15. #15
    Quote Originally Posted by roger wiegand View Post
    My lathe, of late, is driving me crazy. I spent several months turning big heavy green bowls, and have recently gotten back to between-centers work and boxes and such. I think I've either knocked something out of whack or hosed my bearings. (They have never been replaced)

    The lathe is a Conover from 1990.

    The symptoms are constant vibration, increased chatter, and inability to re-mount anything and have it run true. I use a dead center as a small ring drive (like what Oneway describes as a "safety drive") and on other lathes as recently as last week re-mounting is nearly flawless. It was very good on this lathe in the past, now I'm off center by 1-2 mm every time I put the piece back on. If I rotate the workpiece on the ring it goes off center.

    I measured runout on the spindle with a dial indicator. At the front end it is zero to my ability to measure. At the handwheel end of the headstock the spindle is eccentric by about 0.4 mm when rotating the spindle by hand. The points on two different centers describe a small circle as they rotate at speed.

    There is no perceptible motion in the headstock, other than the expected rotation. I can't move the spindle in any direction. It does make a new whirring noise under load when the bearings are loaded.

    Replacing the bearings is something of a project in this machine, so I don't want to overlook some other obvious problem/solution.

    The ultimate solution is arriving from Wisconsin in about 8 weeks , but I'll need this one to be in salable shape then, plus I was planning on making a run of pepper mills for Christmas gifts and I'll go crazy trying to do it with the lathe in its current condition.

    Anything else I should check or try?

    Pictures show how I measured-- I'm no machinist, so please tell me what I'm doing wrong!

    IMG_1610.jpgIMG_1609.jpg
    Any lathe I've ever used including the one I own if you remove the turning you have to mark it how it fit in the spur center so it went back exactly the same way. Anything else and it wouldn't turn true again and would vibrate.

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