weird Z step units

My Z calibrates at 10,000 steps per 1mm. When i calculate the numbers it should be 8,000. I have .9* step motors at 16 micro steps, m5 x .8 Z screws. Am i figuring wrong or am i possibly missing steps on my Z axis? Prints look good, very little banding but there is a little.

360* / .9* = 400 steps per rotation.
one rotation = .8 mm
1mm = .8 x 1.25
400 x 1.25 x 16 = 8,000 steps per mm

Is that not correct?

Edited 1 time(s). Last edit at 10/18/2014 01:19PM by GITRDUN.

Your calculation seems correct, Do you drive the m5 rod directly by the motor or with som belt and pulley? If you have a 16 tooth pulley on the motor and 20 tooth pulley on the M5 rod you will end up with 10.000 steps / mm (20/16=1.25 ; 1,25 * 8000 = 10.000)

/Martin

Edited 1 time(s). Last edit at 10/18/2014 01:56PM by bond.

Direct drive. It is a Prusa I3.

Never mind. I am using marlin firmware and i just noticed that the Z steps are set to 10000.0/1.25 . Why it has /1.25 in it i dont know. but obviously thats it.

that was for 8mm rod which is 1.25mm per revolution.

You could specify yours as 6400/0.8 if you wish

Prusa calculator?
As i think i use 4000 for m5 threaded rod and 1.8º 400step motor with 1/16

So 8000 would be right for your stepper angle

Edited 1 time(s). Last edit at 10/21/2014 07:54PM by pushthatbolder.