Bed calibrated for paper thickness and when printing nozzle in air

Hello !!!
I have calibrated the bead level by thickness of paper. When I start to print a test cube my nozzle stays in air.
When I click start printing, all axis are homed, when Z axis is homed and is in "0" the next step (I don't know for what is) my z axis motor buzz and make noize but not rotating. After this Z is rised 5 mm and lowerd for the first layer hight.(here my nozzle stays in air)
After this first step I tryed to recalibrate... I have done it but again.
I have changed my Z ax home sensor. Until now it was a simple end stop. Recently I have changed it to an opto end-stop, in idea of malfunctioning end-stop switch, but now is the same problem. The opto trigger is a peace of 0.5 mm thin printed wall, that is still no moving or dislocating and miss triggering.
In your opinion what should I test change to resolve my problem.

Thank You for your help!

Sounds like the homing feedrate for the Z axis is too high

I have started changing parts, in idea of faulty part. I have changed the Z axis motor driver, I had green stepstick now I have pololulu stepstick(purple). After I have changed the stepstick I had to calibrate the Z axis from Firmware settings, I have calculated with leadscrew calculator and gave me 4000, but after measuring it was needed to adjust and the final value is 8000. After this i had problem with homing, Z axis moved when I moved from Repetier host but when I wanted to home Z axis the motors just buzzed and didn't rotated. I managed to repair the problem by lowering the feed rate from 4 * 60 to 2*60. But I have still this problem.
I managed to print out good parts(calibration cubes) after the print started.

Tomorrow I will try to lower feed rate to 1, and I will try to film the printing part that I am nat sure what happens and why.

Thanx for fast response!!

You probably want to reduce your micro stepping. Thats to many steps/mm for a 8 bit ardunio type controller.

"0.5 mm thin printed wall" might still be IR optically clear, wrap it in tin foil.

Edited 2 time(s). Last edit at 03/30/2017 11:10PM by Dust.

Hello today I have managed to capture the problem, it seems that the problem comes when I try to print in the first faze the alignment part. the movie starts when I hit "Start Printing" button and this is what happening at my printer. The problem is when Z axis is homed after that Z axis tries to rise 5 mm but only one motor is rotating.
**I have made more tries and once the left hand motor is stopped and the right h. motor is rotating and the other time is vice versa. There is no rule that only one motor is stopped and the other one is rotating.
Can I separate Z motors in two different stepper drivers? Now I have one stepper driver for the 2 motors.
Pls help my and give me idea what to search or modify to resolve this problem.
VIDEO LINK: [www.youtube.com]

Thank You!!

Quote
2*60

i used this setting with 4000 steps/mm and was close to maximum speed for the motors.

8000 steps/mm would indicate 1/32 microstpping with M5 rods
Either reduce your Z microstepping on the controller to 1/16 or try changing the 2*60 to just 100 or lower.

I have selected 8k becouse firt stime the leadscrew calculator calculated me 4k stp/mm but after I have mesured it was only the half of the distance that I wanted.
I have played a little bit with my feedrate, but ain't no good response, I have lowered to 60 but it is the same problem.
From this video [youtu.be] it can bee seen that normally the Z is going slow but when starts to rise or move( after I set it to print out a part) is is fast.

Thanks for help!

It looks like your homing speed is working ok, but the travel speed is still too fast, thats why the left Z stepper stalls after it homes Z