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  1. #1

    X and Y axis move 10x distance they should.

    I am building a briefcase printer from scratch and have run into a problem on my x and y axis. I thought I had configured my x and y steps/mm when I realized that the gcode i was sending was in mm. When I send a g0 x10 command the x axis moves 10 cm instead of 10 mm. This is my first printer so I am not positive I'm not missing something obvious but from what I can find "g0 x10" (I tried g1 too) should move 10mm. My obvious assumption was that the steps/mm where 10x what they should be but at the moment they are x49.82 and y50.07, and if I divide these by 10 I would only get about 5 steps/mm which I think is way too low. When I did try this it did fix the gcode problem but now both axis now move louder and more forcefully than before. There are obvious steps of acceleration that as each axis speeds up and slows down, and changing the acceleration from the default of 100 simply changes when these steps occur. I also messed a little with the jerk but did not see much change. I don't think the original problem was the result of too high of a steps/mm value as before I changed it both axis moved quietly and smoothly with a gradual s-curve, just 10x further than the gcode told it to.

    I am using nema 17 stepper motors with separate belts on each axis and drv8825 drivers on a ramps1.4 board. I have tuned each driver to what I believe is the correct current (my steppers are rated for 1.5A so .75 v on the drivers). I am using a default configuration of marlin with current steps/mm of x49.82 y50.07, acceleration of x100 y100, and jerk of x5 y5, however I intend to change these values.

    Thanks for any and all help

  2. #2
    Sorry if this isn't helpful as I'm no expert but i see there is a G21 in gcode. Could this possibly help?

  3. #3
    For some reason pronterface doesn't recognize g21 at the moment (I may have to enable it in marlin idk), however I have used g20 to ensure I'm working in mm and nothing has changed. However I have tuned my movement feedrate and it has helped quite a bit. The beginning and ends of each movement are still louder and jerkier but once the axis speeds up the movement is smooth. Although because x and y are still jittery when accelerating and decelerating, and that is mostly what it does while printing, most prints are quite jittery and loud. I'm not sure if this is a acceleration or jerk problem or if it has to do with my steps per mm, as my current value of about 5 does seem quite low.

    I have also encountered another problem that may or may not be involved; when fine tuning the Unified Bed Leveling Mesh with the lcd knob one z axis motor doesn't always turn right. One motor turns in small increments just fine, but the other motor sometimes moves a little then moves back a little. My guess is that theres too much pressure on the z screw and the motor is therefore skipping steps, but would kinda expect the other motor to do the same too then. Is there anything I can do to avoid skipping steps?

    My last (maybe) issue is that the motors only really move smoothly at around one feedrate. They move just fine with a feedrate of about 6,000-8,000, however if i want the motor to move any slower it becomes quite loud grindy. I'm continuing to mess with my settings so hopefully I will be able to find the issues but I figured I'd post them anyways in case someone has had any experience with them.

  4. #4
    Well again I don't know much but the first thing that comes to mind is your bearings/bushings are binding or need lubrication. Just throwing that out there.

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