Axis moves in the LCD not reflecting real bed size

Howdy all,

My Mpcnc does not reflect the dimensions of the bed when I move it on the LCD screen and also files sent from Repetier firmware. For example, when I move 20mm on the LCD for x or y the machine moves 100mm on the bed. When I send files designed in Fusion 360 cam w/ mpcnc v10 protocols throught USB or sd card from repetier, the machine crashes into its max limits in both axis even if the file is designed within the bed x800 × y1200 max real milling reach of tool mount. My Mpcnc specs: mks gen 1.4 ,drivers a4988 onboard, motors 1.8°, gt2 belt, 16t, Z t8*2, dual endstop, marlin firmware from Vicious for dual endstop_16t_t8. I am probably forgetting crucial info for troubleshooting, but I feel this is a start for resolution.

CAN someone relate to this problem and point me in the right direction?

Your steps per mm are wrong in the firmware, 5X is not a typical value though.

Best is to test with reptier or the LCD, I can not provide any help with fusion and its post processor as there are far too many setting to get wrong.

Let’s separate this into two problems:

  1. Your steps/mm are possibly wrong, or you don't have the jumpers installed for the steppers to change it to 16th sub-steps. A factor of 5 is odd, though it could be explained by having 20T pulleys and missing some jumpers. It's not hard to check, but under each stepper there should be a 3x2 gang of pins which should be jumpered in pairs. Double check the pulley teeth, too.
  2. I don't use Fusion360 for my cam, but the post-processor needs to be configured properly to set speed limits on each axis. Specifically, Z should be 8mm/s - you may be able to increase it by trial and error to see where you start missing steps. The X and Y should be something like 10-15 mm/s and should be adjusted based on the depth of cut and material you are cutting through. IF you think you have the Fusion360 post-processor setup right, then upload the g-code so we can look at it.
  3. Pictures of your board and your MPCNC would also help diagnose what may be going on.
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First of all, thank you for replying so promptly.

I will be getting some photos of the board and the Jumpers which I did not use previously when I had the board in a Tevo Tarantula printer. Meanwhile, I am posting some screenshots that I have of Marlin firmware and Repetier configuration.


This is picture of my MKS GEN board. Never mind the disconnected drivers for cover removal. The fusion 360 post processor V10 I downloaded from of of the posts here in the Forum. I uploaded to the Fusion 360 post folder unchanged.

Are you getting the movement you expect now?

For the Fusion360 post-processor, Guffy (@guffy) has a github which he updated more recently than V10.

I will try that. So there is a big possibility that the movement disparity of Firmware and the machine is the post-processor?

Yes, if there’s a mismatch in the units (like design is in inches and CNC runs in millimeters). Are you still having a mismatch between requested motion and actual motion? I didn’t see anything wrong with the motion in the video - were the dimensions still wrong?

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Yes I am still having the issue of mismatch of requested and actual motion. The video is done while working a small design, but a bigger design that is not bigger than the bed will crash the axis to its limits. So my LCD shows 200 mm max for both axis, but my bed is 800x1200(I took this measurement from the homed tip of the bit to the max cutting area)

Are you sure you have A4988 steppers? I do not see any jumpers on your board picture to set the sub-steps. Could your steppers be A4982 instead? Try setting the board to BOARD_MKS_BASE_HEROIC which will set the sub-steps via software.

@BT, you are correct!! the steppers are A4982 in the specs for Motherboard MKS Base V1.4, so I changed to BOARD_MKS_BASE_HEROIC in Marlin firmware as you suggested. Should I define _driver_TyPe from A4988 to A4982 or marlin assumes that defining the BOARD_MKS_BASE_HEROIC? Could you please look into the pictures that I sent of my Marlin config_h just to make sure I have the right speeds for this board? thank you in advance

@BT, or should I be using the highlighted info that I got from

I don’t think you need to change the stepper type, just the control board. Sure, try BOARD_MKS_BASE_15. For the steps/mm, looks like is should be

#define DEFAULT_AXIS_STEPS_PER_UNIT { 100, 100, 400, 100 }

The z-axis may need to change depending on your specific lead screw. If you’ve got the typical T8 leadscrew with 4 starts and 8mm/rotation, then 400 is the right number.


The default axis steps needed to be calibrated from 100, 100, 400, 100 to 48,48,400,48, so Z was perfect at 400. Now I can move the X axis on the LCD to 780mm and Y axis after 1000 starts from 0 again. Do you have any info on how to set up the post processor code for Fusion 360?


I’m sorry, but I use Estlcam for my CAM and don’t really know anything about using Fusion360 to generate gcode. If you check out Guffy’s (@guffy) github, he’s got some good information. Ryan also has some basic information on milling that may help, too.

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