Replaced Steppers, Z axis overshoots, I3 Pro B

[M4df4c3]

Hello,

I bought a I3 Pro B from a friend and noticed the previous rods where damaged due to lack of lubricant. I purchased new stepper motors (310mm lead screw length, 8mm diameter, 1.8 degree step angle).

I installed the new motors and steppers can move the extruder carrier up and down without issues.

But the issues starts, once I begin a print. The first layer prints perfect, and then once it begins the 2nd, 3rd, etc. layers, the z axis hops too high, and the layers are too far apart. When the print is finished, it looks like a stretched accordion; very tall, very flimsy and barely intact.

In control, I tried changing the z steps per mm setting from 2560 down to about 2100, this helped slightly, but the setting always resets, and it take over an hour the manually click the LCD button down 500+ steps (I think it needs to be at 1600 or less).

The grooves on the new threaded rods are much thicker than the old ones, so I understand what the problem is. I just hope I don’t have to replace them again. I also cannot find rods with as small as grooves as the originals.

It there a way I can set the z steps per mm in Repetier Host? Or is there another way to changes the z steps per mm? Perhaps in the firmware using Arduino IDE?

Thank you, I am having lots of difficulty with this, anything helps! Let me know if you nee more information than this

-Tony

[rdany62]

Hello,

You may have found solution by yourself, but if not, you can use M92 Z<your Z step/mm> then M500 to save to eeprom.

The rods I had in my kit are 8mm and move nearly 8mm by revolution. The steppers step angle are 1.8°, they have to do 200 steps to do 1 revolution, that is to say with 200 full steps the axis nuts move 8mm. So to move the nuts 1mm they need to do 200/8=25 full steps.
With microstepping set to 8 by the jumpers on the mainboard, the driver has to provide 25*8=200 steps to move 1mm,
with microstepping set to 16, they have to provide 25*16=400 steps to move 1mm,
with microstepping set to 32 (drv8825 drivers), they have to provide 25*32=800 steps to move 1mm.

If you use other rods with different moves by revolution, you have to calculate correct values:
Mrev is the move length/revolution of your rods (in mm/rev),
Sang is the stepper step angle (in °) and Sstepmm is the stepper steps by revolution,
Mstep is the microstepping as set on the mainboard,
and Sbymm is the Steps/mm you want to know.

The formulas are:
If you know Sang but not Sstepmm:
Sbymm = ((360/Sang)/Mrev)*Mstep
If you know Sstepmm:
Sbymm = (Sstepmm/Mrev)*Mstep

You can use online calculator if you prefer (eg. https://blog.prusaprinters.org/calculator_3416/ )

With genuine Geeetech rods and steppers, and with 4988 driver, we have:
Mrev=8
Sang=1.8
Mstep=16
Sbymm = ((360/1.8)/8)*16 = 400 steps/mm

With genuine Geeetech rods and steppers and with dr8825 and microstepping set to 32, we have:
Mrev=8
Sang=1.8
Mstep=32
Sbymm = ((360/1.8)/8)*32 = 800 steps/mm

If your rods are different, measure the length the nut moves while the rod does 1 revolution.
Eg. 1:
you use standard M8x1.25 rod, with drv8825 driverand microstepping set to 32, with Geeetech steppers.
Mrev=1.25
Sang=1.8
Mstep=32
Sbymm = ((360/1.8)/1.25)*32 = 5120 steps/mm

Eg. 2:
you use standard M8x1.25 rod, with 4988 driver and microstepping set to 16, with Geeetech steppers.
Mrev=1.25
Sang=1.8
Mstep=16
Sbymm = ((360/1.8)/1.25)*16 = 2560 steps/mm


Do the calculation with your values, then send M92 Z<Sbymm> to your printer to set the Z steps/mm (replace <Sbymm> by the result, no space between Z and the result), then send M500 to save to eeprom.

You should be able to print a calibration cube and adjust the values of X, Y and Z steps/mm.

I hope this helps even if detailed and you posted nearly 1 month ago

[M4df4c3]

Hello, thank you very much for your response. I am not super knowledgeable on this subject; this is my first 3D printer.

I do not know how to find, Sbymm, Mrev, Sang, or Mstep. However I found another post that accurately describes what I am doing. Here is the link to the bottom image attached: viewtopic.php?f=66&t=69776&p=115237#p115237

The rods that CAME WITH the i3 Pro B are just as you see on the left, and the Z step is permanently set to 2560/mm. I replaced the rods with ones identical to the one on the right. I understand that in order to find the right value, I must use the calculations you provided, but I do not know if the microstepping is set to 8, 16, or 32. I think I need to set the Z step to 400/mm like the image on the right. But I cannot simply do this from the LED screen.

CAN I CHANGE the z step in Repetier-Host? Somewhere in the G-code? (Top Image). I am not sure what you mean by " M92 Z<your Z step/mm> then M500 to save to eeprom." I see this same thing in the post, what is the 'eeprom'?

Thank you for you patience with me, I am very novice with this.

-Tony S