Steps/mm question in Z

Hi guys,

I just finished modifications on my reprap (from 5mm screw to 8mm lead screw from China). Of course I changed the steps/mm in z from 8000step/mm (what I had before), to 6400steps/mm, based on 2 mm pitch and the prusa calculator. I have 0.9 degrees nema 17 and go with DRV8825 drivers and 3 jumpers underneath.
The issue is that with 6400steps/mm, the axis flies over what it should move. Speed and torque are very high.
In order to get it to move correctly 1 cm, I had to go as low as 800steps/mm. Speed is slow, although I modified the feedrate for Z to 300 in Marlin.
Now it moves precisely 1 cm, it is slow and the driver heats up like crazy (I will use a fan for this).

Could you share some of your knowledge? Is 800steps/mm correct for such a setup?

That depends on which lead screw you bought

This is my 1.8°/step Stepper motor
// Typical stepper motors have 200 steps per full step/rev = 1.8°/step, so 1/16 microstepping = STEPS_PER_REVOLUTION_E = 3200
// Z Axis 3200, / 1.25mm pitch leadscrew = 200*16 /1.25 = 2560 :: (STEPS_PER_REVOLUTION_Z / PITCH_OF_Z_ROD)
// Z Axis 3200, / 2mm pitch leadscrew = 200*16 /2 = 1600 :: (STEPS_PER_REVOLUTION_Z / PITCH_OF_Z_ROD)
// Z Axis 3200, / 4mm pitch leadscrew = 200*16 /4 = 800 :: (STEPS_PER_REVOLUTION_Z / PITCH_OF_Z_ROD)
// Z Axis 3200, / 8mm pitch leadscrew = 200*16 /8 = 400 :: (STEPS_PER_REVOLUTION_Z / PITCH_OF_Z_ROD)

This is your 0.9°/step Stepper motor
// Typical stepper motors have 400 steps per full step/rev = 0.9°/step, so 1/16 microstepping = STEPS_PER_REVOLUTION_E =6400
// Z Axis 6400, / 1.25mm pitch leadscrew = 400*16 /1.25 = 5120:: (STEPS_PER_REVOLUTION_Z / PITCH_OF_Z_ROD)
// Z Axis 6400, / 2mm pitch leadscrew = 400*16 /2 = 3200 :: (STEPS_PER_REVOLUTION_Z / PITCH_OF_Z_ROD)
// Z Axis 6400, / 4mm pitch leadscrew = 400*16 /4 = 1600 :: (STEPS_PER_REVOLUTION_Z / PITCH_OF_Z_ROD)
// Z Axis 6400, / 8mm pitch leadscrew = 400*16 /8 = 800 :: (STEPS_PER_REVOLUTION_Z / PITCH_OF_Z_ROD)

I believe you are correct unless my numbers are wrong.

thanks mate. as long as as 800 step/mm is moving correctly 1 cm it is clear I bought the 8mm pitch leadscrew it seems

Cheers!

Quote
vonaurolacu25
thanks mate. as long as as 800 step/mm is moving correctly 1 cm it is clear I bought the 8mm pitch leadscrew it seems

Cheers!

Not really!
You got 4mm pitch leads, since the calculation above is based on 1/16 microstepping, while your DRV8825 has 1/32 microsteps ( with all jumpers set )

Quote
o_lampe

Quote
vonaurolacu25
thanks mate. as long as as 800 step/mm is moving correctly 1 cm it is clear I bought the 8mm pitch leadscrew it seems

Cheers!

Not really!
You got 4mm pitch leads, since the calculation above is based on 1/16 microstepping, while your DRV8825 has 1/32 microsteps ( with all jumpers set )

Was wondering about that but was not sure!

Edited 1 time(s). Last edit at 10/22/2017 08:08AM by Roberts_Clif.