HELP ! Prusa i3 - Z axis bounces 4mm from endstop when first printing

Hello fellow Printers,

Basically i'm new to the whole 3d printing game but now i've got a pretty good jist of it.
My problem is that when i go to print (using cura and repetier host) the axis homes fine, then the axis goes into printing position but the z axis goes down hits the switch and goes back up 4mm (thinking that its at 0). So now its at 4mm and prints in the air.

I've tried adding start code but obvs because it thinks its at 0 it cant lower z by 4mm.
Also, I have changed the recheck/retract from 2mm to 7mm which makes the nozzle go down to home then it goes to the position to print at the correct height (0), however after it gets to this point and the x,y axis move to create the first layer, it suddenly jumps up again.

im thinking that i could move the switch down 4mm, although this could mean that the bounces may become inconsistent.. dunno?
I cant move the bed plate up because the screws come loose.


anyone have any ideas? thanks

Sounds to me like you have a 4mm value set for the Z axis of "Distance after Homing". This should be "#define ENDSTOP_Z_BACK_MOVE" in your configuration.h file assuming you are using Repetier firmware.

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Originally Posted by LuckyImperial

Sounds to me like you have a 4mm value set for the Z axis of "Distance after Homing". This should be "#define ENDSTOP_Z_BACK_MOVE" in your configuration.h file assuming you are using Repetier firmware.

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im using marlin so theres no #define ENDSTOP_Z_BACK_MOVE.... any other possible ideas? :/

In Marlin it should be "#define Z_MIN_POS 0" in the endstop portion of configuration.h.

It could also be that you have an excessive Z-Probe offset distance.
"#define Z_PROBE_OFFSET {0, 0, -5.1, 0} // X, Y, Z, E". Make the Z value less negative.

its not seeming to work either... no idea why its lifting the nozzle. could it be something to do with the test model file that im printing?

fixed it, just removed some start code and moved switch down