Is this the right lead screw?

I just bought this “8mm T8x2 Threaded Rod for Trapezoidal ACME Lead Screw”. Is this the right one to replace my threaded rod on my MPCNC with? I know I probably should’ve asked first before buying it but either way, no biggie.

Running DIV268N drivers at 1/16 steps. Can anyone tell me what the steps per mm is that I would need to enter/change in Marlin?



You should be fine just use my firmware for the rambo mini and change the board to whatever board you have.

Oh OK. I’m using your firmware now, but for ramps T8 threaded rod. So I’m guessing it would be easier to do it the way you said rather than changing the values needed to make it right

Just cut the Z value in half on the ramps version, either way only one edit (I’m 99% sure).

I think on mine might have to be much less than half. My steps per mm on Z right now is 2600. It is a fine thread 8mm rod.

When you said to reduce it by half, did you mean from default 400? I think default was 400?? Could be wrong

Hi John. If this math is correct, then your steps per mm should be 1600.

You are using a TR8*2, which has:

1 Start

2mm pitch

2mm lead.


(motor step angle x driver microsteps) / (thread pitch x starts) = steps/mm

For a 1.8º motor: (200 x 16) / (2 x 1) = 1600 steps/mm

For a 0.9º motor: (400 x 16) / (2 x 1) = 3200 steps/mm


Please someone correct me if wrong.

Hope it helps, Martin.

Forgot to mention, if you have EEPROM enabled you will need to update your steps/mm there too (or just there :P).

Im not at a computer to check but that doesn’t sound right. You can verify by matching the minirambo z steps.

The t8’s should be 4 start.

OK thanks guys,

I’ll have a look at the rambo config.h. I also think this is a 4 start thread

uhmmm, that’s a TR82, or you are using TR88 like stock MPCNC? (

TR88 has 4 starts and a 2mm pitch, so 8mm lead. But for a TR82 is like I said earlier.


If you do have a TR8*8 then your steps/mm should be 400. (x16 microsteps, 1.8º motor)

I can only go by what it is sold to me as, and indeed it is TR8X2

Thanks Martin