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IndustryArena Forum > MetalWorking Machines > Benchtop Machines > Z-Axis Ball Nut Placement - I Screwed Up Instead of Down!!
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  1. #1
    Join Date
    Apr 2005
    Posts
    1268

    Z-Axis Ball Nut Placement - I Screwed Up Instead of Down!!

    :wave: I must apologize for bringing up this old problem with my lathemaster conversion again!!! But, here it is. Please bear with me!
    My problem is that the z-axis sometimes sticks when raising or lowering the head. I'm using a warren ball screw, (3/4" in diameter) with a single ball nut. I have since scored off of fleabay, a second ball nut whcih I'm going to install with a zero backlash washer setup. In preparation for this "upgrade" I was reviewing some old documentation which I downloaded for the IH site (great site) a few months ago.
    The thing I noticed, which had escaped me during the original installation, was the placement of the ball nut relative to the carrier thingamajig!! I placed the nut below the carrier instead of on top as illustrated in the IH depiction. Could this be the cause of the head tending to stick? My nut attemps to "push" that massive head instead of "pulling" it along the ways????
    Wow, if this is the answer, boy do I feel like a dummy?:withstupi
    Any thoughts guys!!!
    Bill from Spartanburg
    billyjack
    Helicopter def. = Bunch of spare parts flying in close formation! USAF 1974 ;>)

  2. #2
    Join Date
    Jan 2007
    Posts
    277
    Hi Bill, Im not going to be any help to you at this point but I am interested in your situation for educational purposes. I have a zay7045m from wholesale tool that I am planning on converting, I had read a lot of your posts about your experience and hope you get yours sorted out. I am trying to research and make a good plan for ballscrews, nuts and bearings. I often break out Mr Overkill in my projects and wondered about going with a 1 inch ballscrew in the Z axis. Maybe that would prevent issues with wear and sticktion, but at this point I dont even know if the 1 in ballscrew would fit inside the column Anyway good luck and please keep us informed on your progress. Thanks, Dave

  3. #3
    Join Date
    Dec 2006
    Posts
    3
    I have no knowledge of mill hardware, except what I have read on this forum. My experience is from a Control Systems background. (Yes, I'm a recovering e-weenie)

    Maybe it is just habbit on my part, but it has become second nature to eliminate potential controls and electrical causes first when diagnosing problems. Intermittant failures tend to make me skeptical of set-up parameters in the control software, grounding problems, supply current, etc. It would be real interesting to see the supply current vs. the control signal when the z sticks. Hooking in a VOM and trying to repeat the failure would be much cheaper and easier than modifying the hardware.

    I am looking forward to seeing the resolution. You have convinced me to purchace a mill from Lathemasters, and I hope that it comes out as well as yours. I may take you up on your offer to cut some mounts, etc., and thanks again for the pics of your conversion.

  4. #4
    Join Date
    Apr 2005
    Posts
    1268
    Hey Guys!
    Thanks for the input! I have an electrical background as well and have checked and rechecked my drivers and servo's during the "malfunctions". I've noted that the servo gear actually turns and the head does not move, then falls (jerks) into place, thus sticking on the ways. I do think, however, that the problem is with "my" installation and not the fault of the lathemaster. It's a damn good mill.
    I truly believe the problem lies with the design and the designer/installer. I have noted that most everyone on this board, when designing, machining or installing anything, goes to the nth degree for accuracy and makes sure that everything fits "just right".
    My approach: I looked at the simple Z axis and well, no problem. So I bought a screw/nut, designed some mounts, had my carrier nut bored and threaded for the ball nut and installed everything!!! Not a problem!!
    But, I reap the harvest from my lack of accurate design.
    So, some advice from a novice (me). Take great pains with every step of the installation and design. Being a machinist means being very accurate, very meticulous, and take pride in your work. If you read this board, you hear this preached daily and I'm in full agreement (hard lesson).
    I'm going to pull my zaxis screw, add another zero backlash assembly and ball nut, pull the carrier and lap everything in, re-install, adjust the gibs, install the ball screw system and take great pains to make sure everything is aligned, moves freely and smoothly and I'll bet, my problems go away. BTW, I'm also going to install gas shocks to counter the head weight. Anyway, thats the plan as soon as I finish my current project.
    Sorry for being long winded but I don't want anyone to think that I'm placing any blame on lathemaster equipment when it rests solely on my sholders.

    Have a great day!
    Bill from Spartanburg:cheers:
    billyjack
    Helicopter def. = Bunch of spare parts flying in close formation! USAF 1974 ;>)

  5. #5
    Join Date
    Sep 2004
    Posts
    5
    Hi Bill

    Not sure if you found the problem but does it happen when going up or only when it's going down? Mine always had the problem going down. I believe that the ways on the z are not quite reinforced enough inside the column towards the middle of the travel. Try this, when it's going down lift up somewhat on the front of the head and see if the sticking improves, mine did. If I tightened the gibs it improved but it got to the point where they were too tight before the problem completely went away. I think the column does not have sufficient support towards the center of travel causing it to flex somewhat. I was planning on adding a pulley and counter weight rather than a strut to the z. I bought another mill before I modified mine and no time since to try my theory.

    Good luck
    Mike

  6. #6
    Join Date
    May 2005
    Posts
    2502
    Adjust the gibs carefully, and keep the ways well lubed. That has worked well for me. In fact, I have the opposite issue. If I forget to lock the gibs, the vibration can cause the Z-axis to drift downwards (manual operation, wouldn't happen with your servos).

    I would think lapping also helps this situation.

    Also, a counterweight system using either real weights or gas springs would seem to help. Try to arrange the attachment point on the head out towards the center of gravity and not right on the ways.

    Best,

    BW

  7. #7
    Join Date
    Jul 2005
    Posts
    12177
    Quote Originally Posted by BobWarfield View Post
    ... a counterweight system using either real weights or gas springs would seem to help. Try to arrange the attachment point on the head out towards the center of gravity and not right on the ways. Best, BW
    Bob has it right. Really the ideal location for the ball screw is also at the center of gravity. When the support from the screw is toward the ways you get an overhung load and the head tries to cant forward jamming the ways. I have a toy on my desk that works on this principle, see the picture. The weight of the bird and the clearance hole on the wire lets the mounting block cant and jam; when you bounce the bird on the spring the block intermittently releases and the bird pecks its way downwards.
    Attached Thumbnails Attached Thumbnails clearance.JPG  

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