mendel z axis steps per mm

read everything!!!

ok I have a techzone lazercut mendel,
[reprap.org]
I have replaced all the electronics and the extruder / hotend
(exactly yeh same as the AO-100 so I KNOW these are 100% correct)
ramps 1.4 pololus w/ overvoltage support
wiring is correct
endstops are correct (thanks nophead)

the real problem is my z axis steps per mm
I have tried several values,
hundreds 1000 2000 3000 4000
I am currently settled at 4500 as I can at least make a 1 inch print without problem, but this is still not correct
as the exact size of the leadscrew is not listed I assume M8, because the m8 bolt fnut fits but is not correct because the m8 screw is fine and the bolt is m8
by plugging in 8/20 (T5 for z axis) and M8 (1.25)I get 6400 or a 5xxx number
at 5000 or 6400 it nose dives into the bed and crashes

I would use the techzone value but I do not know how to add in 16x stepping

can anyone point me in the correct direction or provide a good steps per unit/mm

With motor steps/rev at 200
microstepping at 16 and..
8mm rod @ thread pitch of 1.25mm, then...

Z steps= 200 x 16 / 1.25..

Z axis steps/mm = 2560

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_______________________________________
Waitaki 3D Printer

too low
and as I said before Im running 4500 with problems
acceleration = 5 still gives problems

I don't understand what you mean when you say it nosedives into the bed. This happens when the head is too low, and the steps/mm is used to pace when the carriage is lifted up - it does not come into play when it is homing. One should have nothing to do with the other.

As Waitaki has said, Z calibration is an exact calculation. There should be no estimation involved. If your calculated value does not work, then you either have a different problem or perhaps you entered an incorrect parameter into the calculator. How many steps/rev does your motor make? What microstepping level are you using? What is the thread pitch on your threaded rods? There is no other factor involved.

One other thing I just thought of - Are you perhaps losing steps on the axis? You can usually hear when it happens, and if it is happening, it would mean that the carriage is not being raised up as high as you want - which is your symptoms.

it has a belt and threaded rod, so its not direct drive, sorry if I didnt mention that.
the gears are 8 and 20 T5

waitaki Wrote:
-------------------------------------------------------
> With motor steps/rev at 200
> microstepping at 16 and..
> 8mm rod @ thread pitch of 1.25mm, then...
>
> Z steps= 200 x 16 / 1.25..
>
> Z axis steps/mm = 2560