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  1. #16
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    Quote Originally Posted by NeilS View Post
    Tony - I'm trying to visualise your setup.

    Does your live centre have a male or female thread which is the same as your spindle size?
    Male thread on the live centre, same as the male thread on the spindle, as per smiife's photo above.
    Tony
    You can't use up creativity. The more you use, the more you have. ~Oscar Wilde

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  3. #17
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    Quote Originally Posted by NeilS View Post
    OK, I have since spoken to Enzo at Vermec.

    He will do a one-off for me with an M8 thread added to rear of MT2 and also add Loctite when he presses the bearings into the live centre to keep it in place under tension. As a once-off that will cost me an additional $20, so $119 all up + postage. Should there be enough interest and he were to do a batch of them he said he would setup the CNC machine to do a run and the additional unit cost would come down.
    That's a pretty good price, considering it is a one-off. I'm guessing that Enzo is a tad curious about it himself.

    I hadn't given any thought to the bearing slipping out under load; the Loctite is a good thought. Probably a good idea for the threaded section too, unless you devise a lock-washer or drill tap for a grub screw.

    Tony_A makes a good point, anything turned that way will have to be thick enough to not twist until both ends are up to speed... and then be turned down to size in one sitting.
    I may be weird, but I'm saving up to become eccentric.

    - Andy Mc

  4. #18
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    Quote Originally Posted by Skew ChiDAMN!! View Post
    Tony_A makes a good point, anything turned that way will have to be thick enough to not twist until both ends are up to speed... and then be turned down to size in one sitting.
    Slowing it down when you’re done will need to be carefully controlled too. If the lathe has a brake, the flywheel effect on the live spinning chuck at the tailstock could destroy the piece.

  5. #19
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    Quote Originally Posted by turnerted View Post
    You can buy a transfer mandril from Mcjings for about $50 .This has an M2 taper and an m30x3.5 male thread .This will enable you to mount a chuck on your tailstock .It should not be a big job to drill and tap a thread in the end of the morse taper for a drawbar , after all it doesn't need to be dead acurate . Once you have a transfer mandril you will be suprised how many uses you find for it
    Ted
    Yes, Ted, I did consider the Mcjing offering. As you point out, theirs is a v. good price, but after contacting them they couldn't assure me that the thread adpator component would stay in place with the way I plan to use it. And, I didn't think I had the necessary skills to retro-engineer it myself. Some others on the forum may be more confident in doing so.
    Stay sharp and stay safe!

    Neil



  6. #20
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    Quote Originally Posted by Skew ChiDAMN!! View Post
    That's a pretty good price, considering it is a one-off. I'm guessing that Enzo is a tad curious about it himself.
    Yes, I was prepared for it to be a lot more. Interestingly, one of the earlier sellers that I listed in my first post has since got back to me after saying their unit had no drawbar thread to ask me a few questions. They are now considering adding a drawbar thread to theirs in the next production run.

    Quote Originally Posted by Skew ChiDAMN!! View Post
    I hadn't given any thought to the bearing slipping out under load; the Loctite is a good thought. Probably a good idea for the threaded section too, unless you devise a lock-washer or drill tap for a grub screw.
    Without it getting very complicated with an engineering solution and pushing the price way up, the Loctite fix will be good if it does hold up under reasonable tension. But, I'm glad Enzo is going to be doing it. If I were to attempt it I'm sure the bearings would be all glued together tight!

    Quote Originally Posted by Skew ChiDAMN!! View Post
    Tony_A makes a good point, anything turned that way will have to be thick enough to not twist until both ends are up to speed... and then be turned down to size in one sitting.
    I expect that a variable speed lathe that can be slowly dialed up and down could be essential for long fine spindles. As Colin points out, long fine spindles will be at greatest risk when they are at their thinnest cross section near their completion and during the wind down. This is one of the reasons I was originally looking at the small 50mm chucks which have a lot less mass than a standard 100mm scroll chuck. I also considered Jacobs chucks with less mass again, but they also have a restricted gripping range.
    Stay sharp and stay safe!

    Neil



  7. #21
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    Quote Originally Posted by NeilS View Post
    Smiife, that would be the ideal solution if the thread adaptor will not pull out of the live centre and the Morse Taper is already internally threaded to take a draw bar?

    How is the thread adaptor held in that live centre that you have posted, Smiife?

    So far, I haven't been able to find a MT2 with a live centre that is already threaded ready to take a draw bar. Then there is the issue with the thread adaptor being secured in the live centre so that it will not pull out under tension.

    I have considered how I could drill and tap a MT that is not already threaded, but the challenge there is how do you hold and accurately drill the morse taper once it is attached to the live centre?
    Hi Neil, not too sure how It is held together , pressed together I would imagine,
    I don, t think it would pull apart if thats what you mean , why do you need a thread for a draw bar , surely a chuck tightened correctly and just a 1/4turn backwards on the tailstock would give enough "pull" for your experiment ?
    Cheers smiife

  8. #22
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    Quote Originally Posted by smiife View Post
    I don, t think it would pull apart if thats what you mean , why do you need a thread for a draw bar , surely a chuck tightened correctly and just a 1/4turn backwards on the tailstock would give enough "pull" for your experiment ?
    You could well be right, Smiife.

    I'm just cautious about such matters. If I'm going to play about with a lump of metal spinning at 2k rpm, or more, I'd like to be confident that it is going to stay put in the tailstock. I'm getting too long in the tooth to lose any of them.... : - )




    Sent from my ZTE T84 using Tapatalk
    Stay sharp and stay safe!

    Neil



  9. #23
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    Neil
    I just checked this morning and my Mcjing transfer mandril already has a small recess in the end of the morse taper and can be held in a 120 chuck with longnose jaws with the morse taper pointing to the tailstock .Drilling and tapping a hole should be a breeze .
    I look forward to hearing the results if you get it set up . I had also thought about spindle turning with a "tension" system .
    Ted

  10. #24
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    Quote Originally Posted by smiife View Post
    I don, t think it would pull apart if thats what you mean , why do you need a thread for a draw bar , surely a chuck tightened correctly and just a 1/4turn backwards on the tailstock would give enough "pull" for your experiment ?
    I think you'll be surprised at how much tension you may need to pull out even a tiny deviation.

    It's the classic "tension a cable to pull out sag" problem, except using centripetal forces rather than G in the equation. The straighter the "cable" the more tension is required to remove the same sag amount, quickly approaching infinite tension needed. On paper, anyway.

    Of course, it's possible that on the scale we're talking about here the deviation can be brought into "acceptable" limits... I hope so, my fingers are crossed and I'll be quite content to be proven wrong.

    ('Tis good to see someone actually testing it out; that's what makes the difference between a practical engineer and a University lecturer in the engineering dept. )
    I may be weird, but I'm saving up to become eccentric.

    - Andy Mc

  11. #25
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    Another thing to consider is that a thin piece under tension will try to resonate. This may result in chatter or worst the tool digging in and destroying the piece.

  12. #26
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    Quote Originally Posted by Skew ChiDAMN!! View Post
    It's the classic "tension a cable to pull out sag" problem, except using centripetal forces rather than G in the equation. The straighter the "cable" the more tension is required to remove the same sag amount, quickly approaching infinite tension needed. On paper, anyway.
    I think the benefit lies in not putting pressure on a long thin spindle which will definitely cause it to bow, more than using the tension to hold it perfectly straight.

  13. #27
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    Quote Originally Posted by turnerted View Post
    I just checked this morning and my Mcjing transfer mandril already has a small recess in the end of the morse taper and can be held in a 120 chuck with longnose jaws with the morse taper pointing to the tailstock .Drilling and tapping a hole should be a breeze .
    I look forward to hearing the results if you get it set up . I had also thought about spindle turning with a "tension" system .
    Ted


    Ted, thanks for that information on how the McJing device can be readily held in a woodturning chuck with long nose jaws. Also, that the end of its Morse Taper already has a centre recess hole into which to start the drilling. Any thoughts on how to keep the MT from rotating in the live centre while drilling? My earlier thinking when I thought I might have to do this was that enough masking tape wound around the two components would probably be sufficient if the drilling went up in small incremental sizes.


    Interesting that you have also thought about some sort of tension holding system. I can understand why woodturning developed as it did between centres, coming as it from origins like pole lathe turning, but I'm surprised that there has not been any development of tension holding systems between centres since the introduction of clamping style chucks for woodturners, which we have had now for many decades.

    There is theoretical support for the benefits of a tension system over compression, but almost no published experimental results, and no off-the-shelf workable system that I could find. The best article on the topic that I could find was Dennis Gooding's:


    You will need to be logged on to that forum to see his tables and images. His experimental results showed that a spindle under tension is more rigid and can be turned to a smaller diameter over more length, but the apparatus he use to achieve tension was not a workable solution outside of the experiment.

    I could try to replicate Dennis Gooding's results with his setup, but I though it would be more useful to try to find a workable setup that others can readily adopt if it proves to be worth it in terms of cost and greater turning satisfaction.

    As always, at least try to......
    Stay sharp and stay safe!

    Neil



  14. #28
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    Quote Originally Posted by Bohdan View Post
    Another thing to consider is that a thin piece under tension will try to resonate. This may result in chatter or worst the tool digging in and destroying the piece.
    Yes, Bohdan, that is what this experiment is all about.
    Stay sharp and stay safe!

    Neil



  15. #29
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    Quote Originally Posted by Skew ChiDAMN!! View Post
    I think you'll be surprised at how much tension you may need to pull out even a tiny deviation.
    In Dennis Golding's experiment he got up to 55 pounds of tension to get his result. This is why I think a drawbar will be a necessary component of a workable solution.

    Quote Originally Posted by Skew ChiDAMN!! View Post
    It's the classic "tension a cable to pull out sag" problem, except using centripetal forces rather than G in the equation. The straighter the "cable" the more tension is required to remove the same sag amount, quickly approaching infinite tension needed. On paper, anyway.
    Right, as can be seen in any suspension bridge!

    Quote Originally Posted by Skew ChiDAMN!! View Post
    Of course, it's possible that on the scale we're talking about here the deviation can be brought into "acceptable" limits... I hope so, my fingers are crossed and I'll be quite content to be proven wrong.
    Me too, but if it proves to be a dumb idea then I'm also happy to put it too bed...
    Stay sharp and stay safe!

    Neil



  16. #30
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    Quote Originally Posted by NeilS View Post
    You could be right, Smiife.

    I'm just cautious about such matters. If I'm going to play about with a lump of metal spinning at 2k rpm, or more, I'd like to be confident that it is going to stay put in the tailstock. I'm getting too long in the tooth to lose any of them.... : - )




    Sent from my ZTE T84 using Tapatalk
    Good point Neil , best to be cautious , I was thinking about it today
    And would be better to use a drawbar as you said , belt and braces !
    Cheers smiife

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