different steps/mm for X and Y

Mostly Printed CNC - MPCNC Troubleshooting
1

I have just about completed my MPCNC dual-endstop build. I am using an SKR 1.3 controller, TMC2208 drivers, and the dual-endstop Marlin code.

Using a dial indicator, I am calibrating the machine movement. Y and Z are dialed in pretty close. But, the X is off.

I mean it is significantly different from the Y. Both have the same motors, gears and belts. At 50 steps per mm on the Y, I was getting 11cm movement when I asked for 10cm. On the X it was 7.6cm.

I cannot wrap my puny brain around this, although I can MAKE the X work correctly, I just wanted to understand how this can happen???

 

2

11 when you ask for 10, I would not call “pretty close”. I’m also wondering how you get 50 steps per mm unless you have some unusual motors or pulleys. If your pulleys are large, you will have less force for the same torque, and it will skip steps more easily.

The crown will be distorted, but draw it anyway. Better yet, draw it twice. It will probably give some good clues.

3

Check pulleys and belts. Make sure the belts aren’t steel reinforced. If those are good, I think it would be interesting to swap the x and y plugs and see what happens. If it follows, swap the drivers and see what’s happening.

4

I cannot remember the number of teeth of the pulley, maybe 20 instead of 16.

I will try swapping X and Y motors at the controller board to see if there is some sort of mechanical difference.

Of course, I should have said 11mm to 10mm not cm. This was also the case when calibrating my 3D printer. It was off 5-6 percent as well.

I was kind of assuming that if I get repeatability that I am not skipping…

I am using spread cycle 1/16 micro steps, Not stealthchop.

The motors seem strong, and kept going when I hit a stop and had the limit switch adjusted incorrectly!