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IndustryArena Forum > WoodWorking Machines > DIY CNC Router Table Machines > Avid CNC > My Z-Axis seems to be losing reference
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  1. #1

    My Z-Axis seems to be losing reference

    Hey folks, I first apologize if this has been discussed before, but I have a significant problem that is just beyond my skill level. Second, I apologize for the length of this post as without the proper description, it won't make true sense. I would appreciate any comments toward finding a solution.

    Basic parameters. I'm running an AvidCNC 48x96 with an independent Lenovo PC. I work with Vectic Aspire v11 and use a separate computer for design and place the g-code file (with the proper post processor) to a thumb drive and load that onto the Lenovo with the Mach 4 to drive the CNC.

    I downloaded one of the project files, the Vectric Buffalo Nickel Bank, made no modifications to the file (other than inserting the correct bit feeds and speeds) and cut it with the following toolpaths, 1) 3D roughing .25 endmill, then 1/8 inch tapered ball nose, then a 1/16 tapered ball nose for rest machining (handled by Aspire). Both heads and tails of the nickel are cut from one board in the same toolpath on a board that I have planed to the proper thickness, so I know that there are no discrepancies in material thickness.

    The first cut of the tapered ball nose, using an offset toolpath. into the toolpath, for whatever reason, the Z-height changed leaving a pronounced difference. Even though I knew it was incorrect, I used the touch-plate to zero the next smaller ball nose and it cut the depth properly but it looks horrible since the z height was off.

    So, I thought that maybe this was associated with the offset toolpath and switched to a raster toolpath. Well, same issue occurred. I don't think that this is an issue with the actual model as hundreds of those have been cut and I don't know of any complaints about the model on that forum. I tried to post photos but it won't let me. Any suggestion or advice would be appreciated.

    Would you folks think that this is a machine issue, Mach4 issue or an Aspire issue?

  2. #2
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    Re: My Z-Axis seems to be losing reference

    These kind of issues can be tough to troubleshoot. It's hard to see in the photos how much depth there is to the Z value change. The first photo with the straight line looks like a typical issue where the Z clearance value for a move to a new part location was set too low, but the second photo with the circular error probably rules that out because transfer moves are usually linear. Does this same issue repeat from part to part when using the same machining strategy or does it vary in location and severity?. If the Z discrepancy is random, then it's probably a machine issue - Z axis motor, drive, wiring, controller etc. I had a bad stepper motor on one of my lathes recently that was causing a small random error. I was positive it was a drive or controller problem, but in the end I was wrong and it was a failing motor (ran for too long at too high of a power supply voltage and finally started to fail). The error could also be caused be by some kind of mechanical interference in the Z axis - should be easy to check for that.

    Alternatively you can dig through the gcode and try to find the area where the problem occured (dry run in mach4 perhaps), and check the Z values to see if there is an abrupt change that doesn't seem correct.

  3. #3

    Re: My Z-Axis seems to be losing reference

    Thanks, I appreciate it. The change (about 1/16-1/8) seems to occur at random with or without a clearance toolpath. It only happens on 3-D models of larger size, say over 10". I've checked everything that I know to check so far without success. It has done this since I have had the machine about a year or so. I was still working and didn't have a lot of time to spend as my job had me on the road a good bit. I did contact AvidCNC about this issue and they had me change some settings in Mach4, but that wasn't the solution.

    Interesting thing is that it always happens on larger models and usually at a somewhat random location half way through or less in the model. If it is mechanical, I'll have to remove the whole z-axis mechanism but don't mind doing that. It has done this from the start, so it indeed could be mechanical but if that is the case, why doesn't it occur on smaller 3-D models? I'm perplexed.

    I'm not fluent in g-code, especially thousands of lines of code in such a large model. Is there a software simulation tool for g-code to speed it up and watch? (this model takes about 2 hours to run. Again, thanks!

  4. #4
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    Re: My Z-Axis seems to be losing reference

    Check out ncviewer.com - you can upload a gcode file and animate the motion, view from different angles etc., start and stop from any location by pulling down the code window to any desired location and clicking on the line. I just tried it with a 25,000 line program I uploaded (see image below) and it seems to work well. You can zoom in to look for any Z issues. The only drawback is it doesn't shade the image making it slightly more difficult to find any issues.

    I forgot to mention that you should also check every screw terminal in the control box (especially the Z-axis drive and controller connections) and make sure they are tight. It's not uncommon for something as simple as a loose screw to cause missed steps etc.

    Attachment 484686

  5. #5
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    Re: My Z-Axis seems to be losing reference

    PS - if you try ncviewer the middle scroll roller is zoom, left click to pan, right click to rotate. If you can't find the Z issue in the code then it's a machine, machine controller or mach4 issue. I'm not familar with mach since I use Centroid and others, so I can't help with that.

  6. #6

    Re: My Z-Axis seems to be losing reference

    Quote Originally Posted by cobiecat View Post
    PS - if you try ncviewer the middle scroll roller is zoom, left click to pan, right click to rotate. If you can't find the Z issue in the code then it's a machine, machine controller or mach4 issue. I'm not familar with mach since I use Centroid and others, so I can't help with that.
    Thank you! I will do so!

  7. #7

    Join Date
    Dec 2020
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    146

    Re: My Z-Axis seems to be losing reference

    Check the Z motor to Z ball screw coupler for being tight. Try slowing the Z axis accelerations if the coupler is tight.

  8. #8

    Re: My Z-Axis seems to be losing reference

    Appreciate it very much. I'm struggling.

  9. #9
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    Apr 2022
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    Re: My Z-Axis seems to be losing reference

    Have you tried to run in in a different spot of the table.

  10. #10

    Re: My Z-Axis seems to be losing reference

    Yes, I have tried running on a different table location, same issue.

    I'm going to go out today and check everything from top to bottom and take all the suggestions into consideration. I'll report back to let everyone know what I discover.

    Thanks everyone for your help.

    Mike

  11. #11

    Re: My Z-Axis seems to be losing reference

    Okay, issue is identified. There was an update to Mach4 that corrected this problem. I reached out to Avid and there was an issue with the original Mach4, so I updated and cut and it is perfect. I really think it was an issue with a interface between Mach4 and Windows. Personally, I use a MACbook Pro and just in my opinion, Windows is the worst program ever stolen from IBM. It's pretty bad.

    I want to thank everyone for trying to help me. It was a great outpouring of help and suggestions.

    Mike

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