Z-axis overshooting sometimes


Page 1 of 3 123 LastLast
Results 1 to 20 of 45

Thread: Z-axis overshooting sometimes

  1. #1
    Member
    Join Date
    Jan 2008
    Location
    USA
    Posts
    90
    Downloads
    0
    Uploads
    0

    Default Z-axis overshooting sometimes

    I am having an intermittent issue with my Fineline machine. When I go to run a program it will start with the z all the way up to the safe Z height, and then drop to the piece. Randomly sometimes it will make a barking noise and just plunge all the way into the piece like it gained a bunch of steps and dropped through the leadnut. I have since learned to hold my hand on the Estop button and listen for that when starting a new program, but would like to fix it permanently. I tried lowering the safe Z height and lowering the velocity and acceleration of the axis, thinking it would be a decent bandaid, but it still happens starting 2.5" lower. It only seems to be an issue in the top half of the Z travel. Before I start tearing it apart to figure it out, could it be something else? Are the ACME leadnuts a wear item that needs regular replacement?

    Similar Threads:


  2. #2
    Community Moderator ger21's Avatar
    Join Date
    Mar 2003
    Location
    Shelby Township
    Posts
    35091
    Downloads
    1
    Uploads
    0

    Default Re: Z-axis overshooting sometimes

    Sounds like it's binding. HAve you oiled the screw/nut?

    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


  3. #3
    Member
    Join Date
    Jan 2008
    Location
    USA
    Posts
    90
    Downloads
    0
    Uploads
    0

    Default Re: Z-axis overshooting sometimes

    Hmm, I can definitely say that I have never oiled it. I figured its some sort of plastic piece so it would need it. Its from here: https://www.finelineautomation.com/p...ly?taxon_id=39

    Wouldn't binding make it lose steps, not gain them and plunge into the table? Or is the binding making it skip teeth and drop?



  4. #4
    Member
    Join Date
    Jan 2007
    Location
    Australia
    Posts
    220
    Downloads
    0
    Uploads
    0

    Default Re: Z-axis overshooting sometimes

    compare the rated voltage of the z motor with the actual supply voltage, perhaps.



  5. #5
    Member
    Join Date
    Jan 2008
    Location
    USA
    Posts
    90
    Downloads
    0
    Uploads
    0

    Default Re: Z-axis overshooting sometimes

    Quote Originally Posted by Stewey View Post
    compare the rated voltage of the z motor with the actual supply voltage, perhaps.
    It's not an issue with the motor for once on my machine! I upgraded to Clearpath servos and am utilizing the closed loop portion so the machine will shut off if the servo isn't behaving correctly.

    Could the backlash nut be spinning in the housing? I guess that would actually make it appear to have missed steps, not gained them.

    Hmm... Maybe the fast acceleration at the higher location is overcoming the spring tension. Would increasing the spring tension help overcome this?

    Last edited by drxlcarfreak; 09-09-2019 at 09:39 AM.


  6. #6
    Community Moderator ger21's Avatar
    Join Date
    Mar 2003
    Location
    Shelby Township
    Posts
    35091
    Downloads
    1
    Uploads
    0

    Default Re: Z-axis overshooting sometimes

    If you have Clearpaths, then you can't be losing steps. The coupling may be slipping? Yes, you should definitely be lubricating the nut.

    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


  7. #7
    Member
    Join Date
    Jan 2008
    Location
    USA
    Posts
    90
    Downloads
    0
    Uploads
    0

    Default Re: Z-axis overshooting sometimes

    Quote Originally Posted by ger21 View Post
    If you have Clearpaths, then you can't be losing steps. The coupling may be slipping? Yes, you should definitely be lubricating the nut.
    Exactly my thoughts. Its almost as if I am gaining steps, not losing them though. Like the lead screw is falling through the nut at the top half of the Z travel. This happens only in the top half and in the down direction. When running actual code the Z is dead nuts accurate.



  8. #8
    Community Moderator ger21's Avatar
    Join Date
    Mar 2003
    Location
    Shelby Township
    Posts
    35091
    Downloads
    1
    Uploads
    0

    Default Re: Z-axis overshooting sometimes

    The nut still may be binding, causing the couplers to slip.
    The motors should fault if they lose position, so you aren't gaining or losing steps at all. Must be a mechanical issue.

    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


  9. #9
    Member
    Join Date
    Jan 2005
    Location
    USA
    Posts
    11405
    Downloads
    0
    Uploads
    0

    Default Re: Z-axis overshooting sometimes

    Quote Originally Posted by drxlcarfreak View Post
    I am having an intermittent issue with my Fineline machine. When I go to run a program it will start with the z all the way up to the safe Z height, and then drop to the piece. Randomly sometimes it will make a barking noise and just plunge all the way into the piece like it gained a bunch of steps and dropped through the leadnut. I have since learned to hold my hand on the Estop button and listen for that when starting a new program, but would like to fix it permanently. I tried lowering the safe Z height and lowering the velocity and acceleration of the axis, thinking it would be a decent bandaid, but it still happens starting 2.5" lower. It only seems to be an issue in the top half of the Z travel. Before I start tearing it apart to figure it out, could it be something else? Are the ACME leadnuts a wear item that needs regular replacement?
    It could easily be lost steps, caused by binding or EMI noise problem that could cause lost position also, if it is not going to the command position in the program, can you cut and paste the G-code where this is happening, there could be something in your program also

    Remove your Z axes motor and see if the Z axes move up / down freely, this will eliminate anything mechanical problem with the Z axes

    Mactec54


  10. #10
    Member
    Join Date
    Apr 2016
    Location
    United States
    Posts
    840
    Downloads
    0
    Uploads
    0

    Default Re: Z-axis overshooting sometimes

    Quote Originally Posted by drxlcarfreak View Post
    I am having an intermittent issue with my Fineline machine. When I go to run a program it will start with the z all the way up to the safe Z height, and then drop to the piece. Randomly sometimes it will make a barking noise and just plunge all the way into the piece like it gained a bunch of steps and dropped through the leadnut. I have since learned to hold my hand on the Estop button and listen for that when starting a new program, but would like to fix it permanently. I tried lowering the safe Z height and lowering the velocity and acceleration of the axis, thinking it would be a decent bandaid, but it still happens starting 2.5" lower. It only seems to be an issue in the top half of the Z travel. Before I start tearing it apart to figure it out, could it be something else? Are the ACME leadnuts a wear item that needs regular replacement?


    I used to have a Fineline machine with the ACME screw and had exactly the same problem you are describing. The machine worked fine for quite some time. Then, suddenly the problem manifested. Had me scratching my head for awhile, but I finally tracked down the problem. On mine, the coupling part that clamps to the ACME screw was slipping. When I assembled the parts, I used a product called Vibra-tite as a thread locker. Big mistake. It is not designed for such small clamping screws. I should have used blue Locktite. Anyway, the clamping screws loosened just enough to allow the screw to slip. Messed up a few pieces and made some bad cuts into the spoilboard before tracking down the problem. Dollars to donuts, you have loose clamping screws. I suggest looking there first. While you are at it, you should also check the clamping screws on the upper coupler.

    Note: Even if you used blue Locktite, it may be that you didn't get the screws tightened down enough. They are so darned small, that there is a real risk of stripping out the hex. In fact, when I retightened the screws, I managed to strip the hex on one of the screws. I was never able to get it back loose. I no longer have the Fineline (I built a better machine), but when I took the Fineline apart, I wasn't able to get the coupler off the screw. I could have cut the screw with a dremel, but didn't bother. I wasn't going to reuse it anyway. I mention it as a caution. My advice: GET NEW SCREWS.

    Gary


    The Old Man and the C -----NC


  11. #11
    Member
    Join Date
    Jan 2008
    Location
    USA
    Posts
    90
    Downloads
    0
    Uploads
    0

    Default Re: Z-axis overshooting sometimes

    I actually sprayed the acme screw with silicone last night and it seems to have fixed the issue, now when I power the machine off there is so little friction the z axis noticeably sinks into the table, so I may wipe some off.

    Hmm, I will take a look at those bolts as well to see if I can crank them back down. Hopefully I don't strip them out!

    Thanks guys!



  12. #12
    Community Moderator ger21's Avatar
    Join Date
    Mar 2003
    Location
    Shelby Township
    Posts
    35091
    Downloads
    1
    Uploads
    0

    Default Re: Z-axis overshooting sometimes

    I still think the coupler is loose, and the lack of lubricant caused it to be noticeable. Adding lubricant lowered the torque requirement, so it's no longer slipping. But, it's still loose.

    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


  13. #13
    Member
    Join Date
    May 2005
    Location
    USA
    Posts
    3920
    Downloads
    0
    Uploads
    0

    Default Re: Z-axis overshooting sometimes

    Coupling slippage is a huge issue with the lower cost clamp types. However you wouldn’t hear the slippage thus there was or could still be lubrication or binding issues. In any event considering previous posts I suspect that your whole machine could use a bit of maintenance.



  14. #14
    Member
    Join Date
    Jun 2010
    Location
    Australia
    Posts
    4008
    Downloads
    4
    Uploads
    0

    Default Re: Z-axis overshooting sometimes

    Is this a Chinese machine? I ask because you often find that the Allen head screws they use inside China are rather soft. The hex hole burrs around and the tip of the bolt squashes. Strangle, the Allen head bolts I have bought from China/eBay have been good.
    So ... try replacing the bolts with a better brand, and tighten them up.

    By the by: I have a small Chinese lathe. It goes OK now that I have replaced just about every Allen head bolt in it! Especially in the QCTP!

    Cheers
    Roger



  15. #15
    Member
    Join Date
    Jan 2008
    Location
    USA
    Posts
    90
    Downloads
    0
    Uploads
    0

    Default Re: Z-axis overshooting sometimes

    I took the z axis off tonight to check it out, there were a couple loose nuts there. I tightened it all back up and it seems to be working like a champ now. I think the threads are slightly stripped on one of the couplers, I may at one point do a through bolt drill through both the coupler and acme screw just so that I know it'll never slip on me.

    Regarding maintenance, what all maintenance needs to be done other than cleaning off and oiling the cold rolled steel and the acme threads?

    It is a fineline automation machine,



  16. #16
    Member
    Join Date
    Jan 2008
    Location
    USA
    Posts
    90
    Downloads
    0
    Uploads
    0

    Default Re: Z-axis overshooting sometimes

    I thought I had the issue sorted out, and went to try again today and the bit dove right into my piece. I took the Z-axis apart to install a new anti-backlash nut, and noticed when tightening down all the bolts that one of the acme coupler screws was broken. Not sure how I missed that before, but instead of messing with a screw, I tig welded the acme thread right to the coupler, there is no way that they will slip now. Honestly, I really doubt that it was slipping before because I tried spinning the other end of the amce rod with pliers hard enough to torque it a bit and mar up the threads and it wasnt budging.

    I tried started a gcode (the same one that gave me trouble this morning) about 10 times and the Z seems to have stuck for me. On one run though, it looks like I lost/gained about 1/16" in the X&Y axes as I never touched their offsets when repeating the code over and over. I double checked the tension on the R&P drives, its nice and tight. At this point I think I may be having a computer issue. Is that possible? I am running the newest software 1.2111 with your 2017 screenset Ger, because I was having an EMI issue with my VFD so I run 2ms debounce ignore so the spindle doesn't trip the limits.



  17. #17
    Member
    Join Date
    Jun 2010
    Location
    Australia
    Posts
    4008
    Downloads
    4
    Uploads
    0

    Default Re: Z-axis overshooting sometimes

    2 mS is awfully long. With that sort of filtering you could even miss encoder pulses.
    How about setting the speed and acceleration to painfully low values (5%) and rerunning the test programs? If the system is then OK, your filter length may be a problem.

    Cheers
    Roger



  18. #18
    Community Moderator ger21's Avatar
    Join Date
    Mar 2003
    Location
    Shelby Township
    Posts
    35091
    Downloads
    1
    Uploads
    0

    Default Re: Z-axis overshooting sometimes

    The encoders go directly to the drivers, so wouldn't be affected.

    As I mentioned before, you shouldn't be able to lose position with servos, as the drives should be faulting.

    Also, keep in mind that 1.2111 is a test version which may contain bugs. If you are having any issues, you should be trying the stable release.

    And I don't think any computer issues would cause a loss of position.

    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


  19. #19
    Member
    Join Date
    Jan 2008
    Location
    USA
    Posts
    90
    Downloads
    0
    Uploads
    0

    Default Re: Z-axis overshooting sometimes

    The encoders go directly to the drivers, so wouldn't be affected.

    As I mentioned before, you shouldn't be able to lose position with servos, as the drives should be faulting.

    Also, keep in mind that 1.2111 is a test version which may contain bugs. If you are having any issues, you should be trying the stable release.

    And I don't think any computer issues would cause a loss of position.
    That's true, and I don't see these motors losing position at all with their strength and the speeds I have dropped them to.

    True as well, unforunately, I need a version with the debounce option otherwise my vfd is tripping the limit switches.

    2 mS is awfully long. With that sort of filtering you could even miss encoder pulses.
    How about setting the speed and acceleration to painfully low values (5%) and rerunning the test programs? If the system is then OK, your filter length may be a problem.
    Hmm, I guess that is a decently long time. Unfortunately the software doesn't allow for decimals and 1ms was still tripping occasionally.


    UGH, all this is starting to sound like I need to just pony up and buy a new VFD instead of trying to limp this one along. Are there any decent 2.2kw VFDs out there for the money? My spindle still seems to be operating 100% fine.



  20. #20
    Member
    Join Date
    Apr 2016
    Location
    United States
    Posts
    840
    Downloads
    0
    Uploads
    0

    Default Re: Z-axis overshooting sometimes

    Quote Originally Posted by drxlcarfreak View Post
    I was having an EMI issue with my VFD so I run 2ms debounce ignore so the spindle doesn't trip the limits.
    Quote Originally Posted by drxlcarfreak View Post
    T unforunately, I need a version with the debounce option otherwise my vfd is tripping the limit switches.

    Unfortunately the software doesn't allow for decimals and 1ms was still tripping occasionally.

    UGH, all this is starting to sound like I need to just pony up and buy a new VFD instead of trying to limp this one along. Are there any decent 2.2kw VFDs out there for the money? My spindle still seems to be operating 100% fine.
    New information we didn't know before. As you've already identified, you have a noise problem.

    1. Have you been using dust collection, and if so, do you have it grounded with a bare braided ground wire in the hoses. If you are using PVC anywhere in the system, the static buildup goes way up. I have typical 4" clear hoses and some PVC in my system. The amount of static buildup was incredible. If I got anywhere near the hose with the dust collector on, my hair stood on end. I had limit switches tripping from static within less than a minute of running time. Properly grounded (to earth ground) and the problem went away. I have a ground wire inside the PVC and wrapped abound the outside. Ditto for the hose running from the PVC to the Z axis.

    2. Mactech suggested EMI filter on your incoming power line to the VFD to reduce noise. With the problem you are having, it makes sense to try it. The filters are pretty cheap. I admit that I don't have one, but I'm not having problems with too much noise.

    3. What wire are you using from your VFD to the spindle? Is it grounded at both ends? Improper wire (it needs to have a braided shield) and improper grounding can/will cause noise issues. Igus makes some great cable for VFDs. I'm using IGUS CF6, which is flexible and well shielded.

    4. Is the wiring to your limit switches shielded? If not, it probably should be.

    I wouldn't be too quick to blame the VFD for your noise issues. I believe virtually all VFDs will put out noise. Some just put out more than others. If you are using an HY VFD (one of the more popular Chinese VFDs), you should be able to get the noise down to a usable level. Even if you buy one of the very best/most expensive VFDs, you could still have noise issues. The trick is to filter out/shield out/ground out the noise.

    If you want a lower noise VFD, you might consider an Hitachi model. The WJ200 is popular and gets good r=eviews, although it costs a lot more than the Chinese models. In any event, if you don't take the precautions noted above, you many not solve your limit switch tripping problem.

    Maybe mactech54 will stop by with some pearls of wisdom. He knows way more about VFDs than most of us.

    I still think your over-travel issue sounds mechanical.

    Gary


    The Old Man and the C -----NC


Page 1 of 3 123 LastLast

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  


About CNCzone.com

    We are the largest and most active discussion forum for manufacturing industry. The site is 100% free to join and use, so join today!

Follow us on


Our Brands

Z-axis overshooting sometimes

Z-axis overshooting sometimes

Z-axis overshooting sometimes