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Thread: lathe spindle question

  1. #1
    Join Date
    Aug 2002
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    Post lathe spindle question

    My neighbor just got a small lathe. He is so proud of it. I am glad for him except, the spindle seems to be out. I say seems because the 3 & 4 jaw chucks are out better than .025" - .040". We took the spindle out and put it up in the 4 jaw of my big lathe. I got it to .0004". This is at the front bearing spot and also checking the front of the spindle bore, both no more than .0005" out. I put both chucks on the small lathe I have. The 3 jaw is .006" out and the 4 is .001" out. I figure from that the chucks are ok. The spindle holds the chucks ok, but turns out of round as well as tips front to back. I wondered if the spindle registration point could cause this problem. It is out .001" on the face. The threads look ok but they sure seem to be out.
    Anyone have any ideas? Thanks.

  2. #2
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    Aug 2002
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    I finally saw the spindle was soft. This ment I could chase the threads, which I did. The threads were rolled just slightly, enough to throw the chucks off. I got it true to .0006". We put it back together and now both chucks tir is .002". The back bearing must be off .001" or so. It should be fine for whatever he may need to do.

  3. #3
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    Jun 2002
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    Glad you could solve the problem and help him out. .002"? That's just about as close as I can hold it!!!

  4. #4
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    I was glad to help him. He was impressed that this type work could be done outside a factory. I sort of thought that was one of the reasons he bought the lathe. It turned out, he thought you could only turn stuff. He never even thought of being able to thread or center stuff to .001. I mean his tolerance is + or - 1/4". This was kind of a shock for him, but he is sure happy!

  5. #5
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    Feb 2002
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    Some one post chip a link to "rollies dads..... " method of aligning (or checking alignments of axis (axi?). There were a lot of links.

    I dont think the threads on the spindle have much to do with holding the chucks in line. Isn't it the unthreaded spindle behind the threads and the square shoulder the chuck fits against? And .001 run out at the reister area could easy make several times that amount of wobble at he chuck face.

    I think I am confused!!!! BUt Chip has done his good deed! santa will smile .
    Steve

  6. #6
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    Aug 2002
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    Thanks Steve,
    I am pretty sure it was the threads for the biggest part. After I chased the threads I put the chuck on and tir was .005", istead of .030". Then I turned and faced the spindle register area. It made to where we were only out .002" after assembly. I'm just glad it worked out for him, Rick.

  7. #7
    Join Date
    Nov 2001
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    There have been a bunch of arguments about what alines the chuck. I think it is a matter of religion.....

    But, if the register is off, the threads will cock the chuck. And, the register is usually undersize at least a couple thous, just so you can get the chuck on, or from wear, etc. So if that were so critical, why wouldn't the chuck always be out as much as the register allows?

    The threads look like a cone to me, I would think they aline in combination with the shoulder.

    Here is some more:
    http://www.chaski.com/cgi-bin/webbbs...pl?read=102217


  8. #8
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    OSO: I suspect you are correct. When I said .0001 at the register I should have said shoulder, because I think the shoulder truely holds the chuck or whatever perpendicular to the spindle. I never really thought about the purpose of the register portion.
    I instinctively feel that if the spindle at the register is, for example, 1.495" that the chuck back should be 1.495+ just a smidgen (RCH to be precise). From what the chaski link says, itmakes no difference. so I guess is spent my efforts for naught. My thinking was that the maximum run out would be half the difference in diameters of the chuck back and the spindle. This would be back plate run out not chuck body run out.

    Question for you shop teachers with several lathes (threaded spindle)- Do chucks interchange from lathe to lathe with no loss of concentricy? if the shoulder andthreads do the aligning, they should interchange.

    I stay confused when i think just a little bit
    Steve

  9. #9
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    I was confused on this topic, having studied many postings on what provides the best chuck alignment. Recently, I purchased a new 5" Bison 3 jaw direct mount for my old Maximat 7. The thread is 1.5" x 8 tpi and the registered area measured 1.5000 on my spindle and 1.5005 on the chuck. The chuck threaded on smoothly and seated squarely. No gloat intended but on a 1" steel rod, 1.5" out, runout is +/- 0.0005 ... for now.

    I suspect that while a well centered, accurate spindle thread is important, it is the fit and squareness of the unthreaded area and shoulder which matter most ... in my humble opinion.

    Den

  10. #10
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    The fit of the register, and the squareness of the spindle are what ultimately determine the accuracy of the fit of a threaded chuck.
    The better the fit of the chuck and threads, the better chance of good alignment, but you cannot count on them pulling a 40 or 50 or more pound chuck into alignment.
    All other arguments aside, why do manufacturers bother to continue to make their chucks and lathes with a register, and call it a register if it is not there to register something?
    That being said, if your main concern is accuracy, you should be using a four jaw chuck anyhow.
    Jim H.

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