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Thread: Live center help!

  1. #46
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    Quote Originally Posted by Clint Bach View Post
    Aligning the tips point to point does not definitely mean the axes ( plural of axis?) are aligned. If the axes of rotation are not aligned they are out of alignment even if the tips of the centers are exactly touching. An extreme example is if the tailstock and the headstock were at ninety degrees to each other the tips could touch perfectly. Would they then be aligned? Absolutely not! Assuming the axes could be even slightly misaligned on their axes of rotation (not just point to point) the above reasons can hold true. I don't know how to test for that...

    Another solution to the cones unscrewing could be to put less pressure from the tailstock therefore allowing a slight bit of wiggle. Using just enough pressure to make the spindle run true may solve this problem.

    if you try that report back.

    Clint
    You have a point Clint in the alignment, I was assuming a normal straight lathe bed would be good for alignment, but then again some china stuff isn’t always so precise ;-)


    Have fun and take care

  2. #47
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    Quote Originally Posted by Clint Bach View Post
    Aligning the tips point to point does not definitely mean the axes ( plural of axis?) are aligned. If the axes of rotation are not aligned they are out of alignment even if the tips of the centers are exactly touching. An extreme example is if the tailstock and the headstock were at ninety degrees to each other the tips could touch perfectly. Would they then be aligned? Absolutely not! Assuming the axes could be even slightly misaligned on their axes of rotation (not just point to point) the above reasons can hold true. I don't know how to test for that...
    I'm sorry. This is absurd. The way a lathe is built, there is absolutely no way for the axes to be other than in line. 90 degrees off? I don't think so. I see what you are saying, but it does not apply. It the points line up they SHOULD be colinear. I think, in my opinion they must be, but I could be wrong. A very simple test.
    Well, I guess that if your lathe bed was WAY crooked, you may have a point.

  3. #48
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    Mar 2018
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    I think Clint Bach has a valid point. Alignment of the tips does not mean the head stock spindle and tail stock quill, are running in an exact straight line.

    If you check your alignment with the tail stock quill fully retracted, then move the tail stock rearwards to allow you to fully extend the quill, it is reasonably probable a slight discrepancy may show up when the quill is fully extended. If it isn't exactly the same when fully extended compared to when fully retracted, then the head stock and tail stock are more than likely not parallel.

    My turning club has an issue with one of our lathes, sometimes when doing spindle work one can get a vibration, a quick check as above will sometimes show a minute misalignment which we can shim out. Mainly due to having a swivel head and the fact that the lathe has been used up to six days a week by every dog and his body over the last 10-12 years.

    Also, page 36 of the Laguna Revo 24/36 manual, mentions exactly this and how it is best to re-align the head stock to match the tail stock and why. They have a facility, built in, to allow accurate centre point alignment either by adjusting the head stock, or tail stock.

    The Laguna 24/36 manual, is available online for those who would like to peruse that document.

    Mick.

  4. #49
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    Quote Originally Posted by Clint Bach View Post
    Aligning the tips point to point does not definitely mean the axes ( plural of axis?) are aligned. ...
    This is true. Unfortunately we have little choice but to accept that the ways of the bed are straight and the headstock and tailstock are machined within tolerance. If well machined, removing any twist in the bed will align the entire lathe. If this is not true, get a better quality lathe. (I think alignment is important when one end of the work is held firmly, say, in a chuck, as opposed to a spindle is held between centers.) If holding the free end of a piece with the point of a live center you can assure the point is aligned at that specific distance: with the piece mounted firmly in the chuck spin the wood and mark the center at the end, then bring up the point and see if it is aligned with that mark.

    I do wonder about lathes like the Nova which allow pivoting the headstock away from alignment with the bed. I've never used one so I don't know how easily alignment can be compromised. Since Nova offers a double-ended MT alignment tool "to check and correct the alignment" I'm assuming perfect alignment is not assured without it.

    I've considered ways to check the alignment of the headstock and tailstock of any lathe. I have a laser center finder I use with my milling machine: https://littlemachineshop.com/produc...ProductID=2604 If I mount this in a collet in the wood lathe headstock, the beam will be directly down the lathe bed. If the finder and mount are perfect the red dot will stay at one point when the lathe is rotated by hand. If slightly out, the rotation will describe a circle, the center of which will be the axis of the headstock. The alignment of the headstock with the bed could be checked with precision by moving a target on the tailstock to different positions. Mounting the same center finder in the tailstock could check to see if the axis of the tailstock was properly aligned with the bed. (All bets are off if the headstock spindle or quill machining or the are off or the headstock/tailstock themselves are poorly made.)

    BTW, something which can throw off the alignment of a lathe is a bit of dust or other material in the MT sockets or on the mating surfaces between the chuck and spindle. Chris Ramsey (who turns cowboy hats) said he always cleans the dust spindle and chuck before mounting and especially when remounting a chuck. I try to remember to regularly clean the MT sockets with one of these https://www.woodturnerscatalog.com/p...-Taper-Cleaner Perhaps the worst thing for the lathe spindle is if the inside is scratched or galled leaving a burr. This can happen if something allows a taper to spin when mounted, especially if the spindle is not hardened as in some lathes. Fortunately you can feel this if your finger is small enough and fix it - I had to do that on one lathe.

    Regardless of the type of axial misalignment Clint describes, I still think the OP's problem can be eliminated by replacing the cone with a short snug cylinder with a shoulder, a "plug" as someone well described it. Bring up the tailstock while the piece is spinning to support this plug. If the point of the live center is aligned with the center of rotation at that point, all should be well, even if the overall alignment off.

    JKJ

  5. #50
    Even IF (big if) the bearing bores are perfectly in line with the guides on the bottom of the headstock, and IF the quill bore is bored perfectly in line with the guides on the bottom of the tailstock, and IF the bore in the quill is perfectly in line with the OD of the quill, and IF the axis of the quill and the axis of the head and tailstock are at exactly the same distance above the bedways and IF the axis are on exactly the same horizontal plane, there is still some clearance between the guides on the bottom of the headstock and tailstock and the bedways.

    If that clearance is only .002" and the distance between the guides is 6", then it is is possible to have a .002" parallel offset if both guides are against the same side of the bedways. The situation is much worse if one guide block is against one side and the other block is against the opposite side. This could lead to an angular misalignment of as much as .0007"/inch.

    At the end of a 6" long cup that yields over .004" misalignment. And, the big IFs mentioned above are very likely to not be perfect.

    Regardless the amount, be it .004" or more likely as much as .04", the loading on the cone will not be uniform. There will be a greater force at some position of rotation. That position will remain in a fixed phase of rotation.

    The pitch diameter of the male threads of the center and the pitch diameter of the female threads in the cone are not exatcly the same. There must be some clearance for the two to easily assemble. If the clearance is only .002", then the difference in the two pitch diameters is .002"x pi, or about .0066"

    The uneven loading causes the smaller male thread to turn ever so slightly faster that the larger female thread. Each revolution requires the smaller male thread to make up that extra .0066" by advancing a few degrees.

    Imagine putting a 12" diameter wheel inside of a 13" diameter hoop with the wheel setting on the bottom of the hoop.

    If you turned the 13" diameter hoop one revolution, the wheel would turn 1.125 revolutions.

    This is what is happening between the male thread on the center and the female thread of the cone. I have seen it happen often on my and other lathes.

  6. #51
    Quote Originally Posted by Clint Bach View Post
    Aligning the tips point to point does not definitely mean the axes ( plural of axis?) are aligned. If the axes of rotation are not aligned they are out of alignment even if the tips of the centers are exactly touching. An extreme example is if the tailstock and the headstock were at ninety degrees to each other the tips could touch perfectly. Would they then be aligned? Absolutely not! Assuming the axes could be even slightly misaligned on their axes of rotation (not just point to point) the above reasons can hold true. I don't know how to test for that...

    Another solution to the cones unscrewing could be to put less pressure from the tailstock therefore allowing a slight bit of wiggle. Using just enough pressure to make the spindle run true may solve this problem.

    if you try that report back.

    Clint
    Clint,

    You could "test for that" by using a double reverse indicator method (after allowing for indicator sag), or by using some relatively expensive laser alignment equipment. I have used both methods, the laser is far and away the more accurate.

  7. #52
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    Quote Originally Posted by Dale Miner View Post

    Imagine putting a 12" diameter wheel inside of a 13" diameter hoop with the wheel setting on the bottom of the hoop.

    If you turned the 13" diameter hoop one revolution, the wheel would turn 1.125 revolutions.

    This is what is happening between the male thread on the center and the female thread of the cone. I have seen it happen often on my and other lathes.
    An interesting and awesome explanation! Thanks! And I thought it was only me that seen this..... I was in denial, HUH? Am I seeing things? This can't be happening, did I tighten that down? Kept happening......

  8. #53
    What Dale said.

  9. #54
    Is there any vibration while turning the wood? Vibration combined with Dale's thoughts, and a tailstock that creeps can be enough for the cone to work loose. My first lathe had a Reeves drive and the vibration that it created was sufficient to cause everything to rattle loose ... tailstock, banjo, toolpost lock, headstock. I apologize if this idea has already been kicked around.
    Last edited by Bill Boehme; 05-20-2018 at 2:08 AM.
    Bill

  10. #55
    Ricc,is the live center and cone both, made by the same company? if not, that could lead to your issues. Or another possibility, is the cone and live center the same thread? Could one be metric, and the other be imperial? I have a hard time believing this could happen, but you've stated that it's happened with your buddy's live center as well as your own. So, it's obviously happening, but I be darned if I can envision how with the threads being as they are.
    Len

  11. #56
    Join Date
    Mar 2005
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    Quote Originally Posted by Len Mullin View Post
    Ricc,is the live center and cone both, made by the same company? if not, that could lead to your issues. Or another possibility, is the cone and live center the same thread? Could one be metric, and the other be imperial? I have a hard time believing this could happen, but you've stated that it's happened with your buddy's live center as well as your own. So, it's obviously happening, but I be darned if I can envision how with the threads being as they are.
    Len
    Same Manufacturer and same thread. No tailstock creep. No vibration as I am turning. The bearings in the live center are good and not dragging. A lot of good thoughts have been shared and I thank you all for your input. I ahve tried a couple of the suggestions (like the plumbers tape, checking alignment, etc). I can't afford a Nova live center as John K.J recommended as I'm on disability. But, I will try a couple of the other suggestions like turning a wood cone that Leo suggested, and maybe trying to find someone to drill and tap the aluminum cone for a set screw.

    Keep ideas coming if you think of anything else.

    Thanks
    Ricc

  12. #57
    Join Date
    Jan 2007
    Location
    Orange County, CA
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    Try checking the run-out of the aluminum cone and live center. Put a short dowel, wood or metal, in the live center to lock it. Install the cone and place the assembly in the spindle taper. Run the lathe to check the run-out of the cone surface. This process can be used to true up the surface if required. Use a cutoff tool or a round nose scraper that will limit the width of the cut.

    If you make a wood cone, use this process for the final true-up of the cone.

    Note : You should verify that the center point of the live center runs true in the lathe spindle before checking the cone run out.
    Last edited by Joe Kaufman; 05-21-2018 at 11:31 AM.

  13. #58
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    Mar 2005
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    Quote Originally Posted by Joe Kaufman View Post
    Try checking the run-out of the aluminum cone and live center. Put a short dowel, wood or metal, in the live center to lock it. Install the cone and place the assembly in the spindle taper. Run the lathe to check the run-out of the cone surface. This process can be used to true up the surface if required. Use a cutoff tool or a round nose scraper that will limit the width of the cut.

    If you make a wood cone, use this process for the final true-up of the cone.

    Note : You should verify that the center point of the live center runs true in the lathe spindle before checking the cone run out.
    I will give it a try Joe. Thanks for the suggestion!

    Ricc

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