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Z travel problem

Discussion in 'Troubleshooting and Build Support' started by TigerPilot, Oct 25, 2013.

  1. TigerPilot

    TigerPilot Well-Known Member

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    I have a problem with my z axis that I can not find the solution for.

    Every time I go up on the z axis I lose 2 or 3 thou over a distance of 2.5". When I go down I don't lose nothing. When I cut in 3D, with close to a 1000 up movements, even if they are small, it accumulates. Up to about 0.2". I checked my calibration, I checked the reference voltage, I checked the backlash, I made sure the acceleration is the same on all 3 axis' (it was not initially). Everything is fine.

    As I've said, it's only on the up movements that I lose distance, not steps (I would hear it if it were steps that I lose). The down movement is fine. I checked it with a dial indicator.
     
  2. foamlvr

    foamlvr Member

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    Sounds like something slipping. If not a set screw then maybe the plastic part of one of the pulleys. Look at where the bearings for the Acme screw are mounted, is the wood broken or bulging? Did you change driver boards? A few years back we got some boards with bad opto isolators, that would do just what you are describing. You've been running that machine quite a bit, maybe the zero backlash nut is worn out.
     
  3. TigerPilot

    TigerPilot Well-Known Member

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    I didn't change the driver board. It's the original that came with the first batch of PhlatPrinter III. I'll try to switch the z and y motor connection on the board to see if it will persist.

    The plates where the Acme screw bearings are, are new. I had changed them not to long ago. What boggles my mind is that all those physical things that you mentioned should not, I think, make the error on the up only and not on the down and if they do, shouldn't it be non accumulating? As compared to what I encounter, that it is accumulating and goes farther and farther down.

    As I've said in the OP, I did look at the backlash possibility. I had increased the backlash value and it didn't make a difference. As it shouldn't have. Backlash would have been on the up as well on the down, which is not what I have.
     
  4. foamlvr

    foamlvr Member

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    The only thing I mentioned, that I think it would really be is the plastic part of a pulley slipping, and only because gravity would make it slip going up but not down. I turn mine by hand quite a bit, and it is always easier to lower the Z than raise it. Those pulleys seem tight even if they are slipping. Just a thought,, are you still running the big pulley on the stepper and the little one on the screw? That big pulley puts a lot of torque into the hub. I'm running equal size pulleys on the stepper and screw. It's been quite a while since I did it, but I think I did it so I would get a decent steps per in count without micro stepping.
     
  5. Flashsolutions

    Flashsolutions Active Member

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    When going down you have the weight of the gantry working for you. Going up makes the stepper work harder because of the weight of the gantry has to be lifted and gravity works against you.

    My guess is that there is slippage in the pulley either at the set screw not holding tight to the shaft or it could be dirt and debris between the gear teeth or worn pulley gear teeth or even a belt but probably not likely to be the later.

    However there is also the possibility that the stepper motor is weak, or the controller is bad. The early round steppers were notoriously bad and if I remember right, I think there were shelf life issues with them.

    Try holding the pulley with your fingers (with the belt removed) to see if the torque is strong enough to resist your trying to stop it. If you can stop it from turning by holding it, you could have stepper/controller issues.

    If the set screw is not holding or it is worn, you may or may not be able to detect that visually.

    Too much belt tension might also cause extra strain on the stepper. Too loose and the belt could slip teeth.

    There are a lot of variables to contend with. Perseverance and a bit of luck and you should be able to isolate it. Can't tell you how many times I have stumbled across a solution by accident while fiddling with things.
     
  6. TigerPilot

    TigerPilot Well-Known Member

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    I too have the pulleys changed to equal size, small.

    I'll take a closer look today at the pulley and see if it is slipping or if it is a little damaged and slipping internally. Didn't think of it before Flashsolutions and you mentioned it. That's why I posted here first, before I asked that question at CNCZone. You guys here are awesome.
     
  7. TigerPilot

    TigerPilot Well-Known Member

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    Did you hear about the guy who jumped off the Golden Gate bridge this morning? No? It was me!!! :D

    I can't believe I spent all this time to try to solve the problem and in the end it was the set screw on the motor pulley that was not 100% tight. Oh man, I hate those set screws. I always change them, if it is possible, to screws with heads. I had it changed on the spindle side but not on the motor side. It's done now. Those set screws can not be tightened as well as screws with heads.

    Thanks for the help, guys. Now it's off to cut some extensive 3D parts. :)
     
    swarfer likes this.
  8. rcav8r

    rcav8r Moderator Staff Member

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    Yep, the set screw was my first guess when I read your first post...been bit by that one myself.
    Something that wasn't mentioned, and obviously not your issue,was those white wiring blocks. They used to cause my fits with missed steps and such. I replaced with soldered 4 pin headers (for easy removal if needed)
    Hopefully someone will remember this if they have "weird" stepper issues, but now that you know you won't have the problem :rofl:
     

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