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PM-940M CNC Z axis bearings?

Discussion in 'PRECISION-MATTHEWS' started by merb7880, Jun 3, 2017.

  1. merb7880

    merb7880 United States Swarf Registered Member

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    Relocated our PM-940M CNC from Western PA to FL. When we pulled the machine from its base, we found this bearing and nuts on the floor inside of the base. See attached image. My assumption is they came off the Z axis somewhere/somehow, and now I'm on a mission to put them back in the correct order. I have no idea what that order may be. Does anyone have any info on this, pictures, descriptions, anything?

    When I asked Matt over at PM his only guess is "it may have came off a ball screw end from somewhere"

    I'm pretty sure that's the case, but I was hoping for some diagrams or something.

    I've been trying to find any info I could on this, but to no avail. I did see a picture once of an assembled z axis that would have probably helped, but can't find it anymore.

    Does anyone know where these belong, and how to get them back to their home? Also, we have no idea how long they were off, but were still using the machine to make parts. Hopefully it's not a big deal, the machine still seemed to function properly.

    Thanks!
     

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  2. JimDawson

    JimDawson Global Moderator Staff Member Director

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    Based on the condition of the parts in the picture, it looks like they have never been installed. I'm guessing you may have gotten some ''bonus parts''. If the nuts were not installed, I would expect massive backlash in one of the axes.
     
  3. cut2cut

    cut2cut United States Active Member Active Member

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    IMG_1045.jpeg
    It probably came from the lower end of the Z axis. I removed them because my Z axis made noise when it would "whip" and bind a bit against the hand crank gears on every rotation of the screw, creating a noise I didn't like hearing all the time. Either someone forgot to install yours, or they were extras. This is what mine looked like BEFORE i did anything ( see pictures ). I suppose it being there would act as a failsafe if your upper Z bearing nut ever failed or was unscrewed it would result in the entire Z ball screw crashing down with the head.

    I had to lift the Z screw about 7 inches to remove the hand crank assembly entirely. Wasn't a "fun" easy task.
     

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    Last edited: Jun 3, 2017
  4. merb7880

    merb7880 United States Swarf Registered Member

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    Thanks guys. From the pictures, i can definitely tell its from the z axis ball screw end. I can't tell the order they would sit on the screw, and I really wish this electrical cabinet wasn't attached to the rear column, blocking access to the screw. I'm wondering how big of a deal it would be if I just left them off. cut2cut you said you removed yours because of a noise, do you think it has impacted the machine in a negative way at all since removing>? How fast do you rapid on your axes? The only way I think I can access it would be to try to reach from underneath inside of the base.... maybe....
     
  5. cut2cut

    cut2cut United States Active Member Active Member

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    I don't think it is an issue if its not there, unless you use the hand crank.

    will respond tonight further...

    Jake
     
  6. cut2cut

    cut2cut United States Active Member Active Member

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    One negative to removing this lower set of bearings and hand crank gears is the head can creep down on its own weight because the hand crank gears/assembly acts as friction. I've removed the quill and transmission gears, and oil so the head is not as heavy so I don't have to worry as much about the head creeping down when the machine is off. It was marginally too heavy before I removed the weight.

    I only use 50 inches per second rapids in the Z. Someday I hope to replace the steppers with bigger servo motors. Can't say what the standard steppers can handle but I keep it on the very conservative side.

    Jake
     

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