Step/mm Error - Nema 17 0.9°/step

Following the replacement of my previous motors, I am trying to recalculate the steps/mm to be set in the Arduino firmware.

The value that makes things work is 1600 for the Z-axis (the one I'm interested in), but theoretically, it should be 800.

I can't figure out the conceptual error I'm making, so I will now list my components and present some hypotheses in the hope of resolving it with your help.

COMPONENTS LIST:

Motor Link (Nema 17 with 0.9°/step): [www.omc-stepperonline.com]

Printer: Prusa I3

Driver: DRV8825 with 1/16 microstepping

Board: RAMPS 1.4

Screws: [www.amazon.it]

Possible errors:

1- The lead screw mentioned in the screws of my 3D printer purchased on Amazon is 4mm, so it is actually a 2-start screw, not 4 as indicated.

2- There might be an error in the firmware, and the microstepping is not actually 1/16.

0.9 steppers are 400 steps per rotation * 16 micro stepping = 6400 steps per rotation with micro stepping.

as for your lead screw, you linked to your-account order-history, no one but yourself can see this

If it has 4 mm per rotation then the steps/mm would be 6400/4 = 1600

Edited 3 time(s). Last edit at 07/09/2023 11:04PM by Dust.

Hello and thanks for your answers.
I am afraid that the lead of those screws is 8mm. It makes things really unaxpected.

Screws:
Cnloyua 2pcs 300mm T8 in Acciaio Inox Filettato Rod Piombo + T8 Dado, per Macchina Stampante 3D ASSE Z, Vite Guida Stampante 3D, Sostituzione per Ender 3 / Ender 3 PRO/Ender 5 / Ender 5 Plus

lead screw does seem to be 8 mm per rotation

so what does that leave... wrong micro stepping

You say you have drv8825 at 1/16th ie jumpers are set to low (off) low (off) high (on)

I suspect you really have 1/32 micro stepping

0.9 steppers are 400 steps per rotation * 32 micro stepping = 12800 steps per rotation with micro stepping.

At 8 mm per rotation then the steps/mm would be 12800/8 = 1600

What I think is happening is your ramps is a weird but not uncommon one.

Even though you removed ms1 and ms2 jumpers under the stepper driver, the pcb has wire links under the jumpers, so you cannot change them

So they are always set to High (on) High (on) High (on) which is 1/32 micro stepping on a drv8825


Check with a multi meter on ms1 pins with jumper off, check for continuity. It should be open, but I suspect they will be connected

Edited 3 time(s). Last edit at 07/10/2023 03:56AM by Dust.

It seems reasonable, I'll check later with a multimeter.

Anyway, now that the mystery is solved, I wonder how I can set it right and whether 1/32 microstepping makes a difference with respect to 1/16 microstepping.

Thank you once again; you have been really insightful.