Z axis measurement problem

Good morning all.
First, sorry for my English, I’m French and I’m using Google Translate.
I just finished editing my MPCNC and I have a problem on the Z axis.
If I want to go down the Z axis by 5 mm, I have to ask him to move about 30mm. The X and Y axis do not pose a problem, only the Z axis. Has anyone ever had this problem?
Thanks in advance.

That has to do with your leadscrew/drivers/firmware. Can you specify what you decided to use.

This lead screw advances 8mm per revolution: https://www.amazon.com/gp/product/B01HBHUSPQ

This lead screw advances 2mm per revolution: https://www.amazon.com/gp/product/B07QXYT9MH

The default steps per mm assume the first type (8mm per revolution), but if you are using the second type the movement will be 1/4 of what you request. You can fix this by changing steps per mm in the firmware but you have to be careful to reduce the maximum Z speed because the motor can only go so fast and if the motor goes too fast then it will skip steps and you are likely to crash.

Thanks for your help. For the leadscrew, I ordered this one : Leadscrew

My drivers are DRV8825 and the firmware I took: MPCNC_Ramps_T8_16T_LCD_32step

Can you do an exact measurement so we can figure out what is wrong, if you tell it to move 10mm, how far exactly does it go? Does it make nasty sounds when it is moving (binding or too fast), How are you telling it to move (software tellng it to move to fast), does your Z axis move easily with your fingers when powered off (binding)?

I have just taken a step. When I ask from the LCD to Z axis to go down or climb 10mm, it only moves about 2.3mm. No unpleasant sounds and the axis moves easily when the steppers are off

Microstepping not set correctly? That could throw things off by a multiple of 2. (10 / 4 = 2.25 ~= 2.3)

Just a thought…

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That leadscrew looks like a 2mm advance per revolution instead of 8mm, which would make everything move 1/4 the requested amount.

Change steps per mm to 4x the value in firmware for Z (3200 instead of 800) on DEFAULT_AXIS_STEPS_PER_UNIT


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