Homing issue

We are building a Prusa i3, with the kit from 3dPrinterCzar. I am having an issue homing the printer. I am using Pronterface to control the printer, with Marlin firmware. If I home to each axis individually, everything works fine. If I press the All-Home button, it homes the X-Axis correctly, the Y-Axis correctly, then moves the X & Y to around 75 or 100mm each and then homes the Z-axis. If I understand the expected behavior, it should end at 0,0,0 not 75,75,0. I'm confused as to why this is happening. Any advice is appreciated.

Thank you,
Matt

Ok, I see the area in Configuration.h that causes this to occur. It is Z_SAFE_HOMING, which causes the nozzle to move to the center of the print area.
This makes sense, but my problem is more specific.

If I issue a G28 command, when it gets to the Z-axis it just hits the limit switch, and raises it up slightly. If I then issue command M114 to get current positions, it is NOT at home on the Z axis. In fact, it has chosen a home well below the limit switch.

SENDING:M114
X:68.00 Y:68.00 Z:10.88 E:0.00 Count X: 68.00 Y:68.00 Z:10.88

Why is this true? Obviously, if I send a move command on the Z axis now, I crash into the glass.

Problem solved: Bed Auto Leveling was turned on. This causes the behavior of the homing function to change drastically. Now that i have turned it off, homing occurs properly now.

-Matt

Quote
mappler
Problem solved: Bed Auto Leveling was turned on. This causes the behavior of the homing function to change drastically. Now that i have turned it off, homing occurs properly now.

-Matt

I love you!

I also have czar's printer and never knew how to fix that annoying problem.

For me it was the same, after doing m114, the Z automatically added 10.88 mm... so each time i wanted to go to 0, the print head crashed with the bed...
Usually i never homed, just moved each axis until reaching the end switch, then set 0 with G92.

Thanks for sharing.

-Marcos