Z-AXIS moves only 25% of what it should

New Home Forum Mostly Printed CNC – MPCNC Troubleshooting – MPCNC Z-AXIS moves only 25% of what it should

This topic contains 11 replies, has 5 voices, and was last updated by  Jay 2 months, 1 week ago.

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  • #104965

    Jay
    Participant

    I just installed a new makita spindle on my MPCNC and wanted to finally try cutting something instead of just drawing. That’s where I noticed that while X and Y movements are very precise, the Z movement is exactly one fourth of what it should. If I try moving 10cm the Z axis from the control panel it moves exactly 2.5 cm. All the other motors travel perfect distances, but the depths are all 75% off. What could it be that causes this strange problem? Is there some setting I can tweak to make the motor spin 4 times more?

    #104969

    Jay
    Participant

    I modified the DEFAULT_AXIS_STEPS_PER_UNIT from 800 to 3200 to correct the movement. This in theory should have worked but in reality it generates some strange behaviours where it doesn’t really move the right amount during a cut. It carves a pocket and then when it’s time to do the finishing pass it does it in the air…in the simulation this setup previews correctly so I’m pretty sure it is something that has to do with my Z axis issue.

    #105002

    Ryan
    Keymaster

    What hardware and electronics are you using?

    When you make such giant numbers to move the Axis your CPU can not handle higher speeds. Try g0 Z20 F100, if that works correctly you just have a speed issue.

    1 user thanked author for this post.
    Jay
    #105048

    Jay
    Participant

    I created a .gcode file with only “g0 Z20 F100” inside, when I launch it I get no motion or feedback whatsoever from the machine, I’m not entirely sure what the result should be but when I launch it it’s like I did nothing.

    Anyway with the DEFAULT_AXIS_STEPS_PER_UNIT set to 3200 I managed to get some test jobs done in styrofoam. Considering what you just said, probably the height issues I’m having are because it sometimes skips some fast movements due to my 3200 steps setting. At moderate speeds it all works fine for now.

    I’m using the lcd dual endstop firmware, and the hardware suggested for the arduino/ramps build, I’m using cheaper clones for the arduino and the ramps, and the same drivers shown in your build instruction, plus generic chinese nema 17 motors off banggood.

    I don’t know if I’m allowed to post links, it’s just to show what I’m using:

    Ramps: https://www.amazon.it/gp/product/B07BSRS9WS/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

    Mega: https://www.amazon.it/gp/product/B071W7WP35/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

    Stepper Drivers: https://www.amazon.it/gp/product/B07K9ZB7M5/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

    Motors: https://www.banggood.com/Nema17-59Ncm-2A-1_84-lead-48mm-Stepper-Motor-For-3D-Printer-CNC-p-1252415.html

    #105067

    Ryan
    Keymaster

    I created a .gcode file with only “g0 Z20 F100” inside, when I launch it I get no motion or feedback whatsoever from the machine, I’m not entirely sure what the result should be but when I launch it it’s like I did nothing.

    Run it from repetier’s command line.

    You did not show your leadscrew.

    I suggest your rapids and plunges no more than 8mm/s, if it is a regular piece of all thread.

    1 user thanked author for this post.
    Jay
    #105073

    Jay
    Participant

    Right, here is the leadscrew.

    What should that code do? I mean How do I know I’m having a good or bad result?

     

    #105081

    Barry
    Participant

    It will move the z axis up 20mm.

    1 user thanked author for this post.
    Jay
    #105112

    Bill
    Participant

    Yeah, that lead screw has exactly one quarter the pitch. It’ll have to be spin four turns to get the same as one turn with the stock screw.

    1 user thanked author for this post.
    Jay
    #105117

    Jay
    Participant

    Crap! I thought that T8 indicated one and only one type of screw. I can’t believe you can have 2 screws so different under the same name! So I need a T8 screw with a 8mm pitch…

    #105237

    Barry
    Participant

    Crap! I thought that T8 indicated one and only one type of screw. I can’t believe you can have 2 screws so different under the same name! So I need a T8 screw with a 8mm pitch…

    It’s the X2 part you need to keep an eye on.  The T8 just means it’s an 8mm diameter trapezoidal leadscrew.  The X part is the thread pitch.  You can get different pitches to do things like faster movement, or more torque.  The higher the pitch, the farther it will go per revolution, so faster, but less torque.

    1 user thanked author for this post.
    Jay
    #105258

    Jamie
    Participant

    Crap! I thought that T8 indicated one and only one type of screw. I can’t believe you can have 2 screws so different under the same name! So I need a T8 screw with a 8mm pitch…

    I had to educate myself on this too.  Technically, the “pitch” is the distance from one thread to the next, but these lead screws have “multiple starts” which means there are multiple helixes around the screw and the nut advances multiple threads each revolution.  The “lead” is the distance traveled per revolution, which is where you want 8mm.  But the pitch might still be 2mm.

    Looks like Ryan’s Amazon link needs fixing; this is the one I got: https://www.amazon.com/OctagonStar-L300mm-Start-Screw-Printer/dp/B01HBHUSPQ

     

    2 users thanked author for this post.
    #105528

    Jay
    Participant

    Got myself a “4 starts” T8 off amazon  and fixed the problem. Thank you all very much for the prompt support.

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