Nozzle going below Z-home before first layers

Hello,
I am having a very weird problem in my Prusa i3. While starting the print the nozzle goes to X,Y,Z home (the corner), at this point the distance between nozzle and bed is perfect. Now to print, the extruder moves towards the print location but also simultaneously goes down (with the help of z motors). The screw puts excessive pressure on the Z end stop. The nozzle gets blocked because its touching the bed and filament doesn't extrude causing the extruder motor to give a 'tak-tak' sound.

I have already checked that there is equal distance between hot nozzle and bed at every X and Y combination at Z home.

As far as I have understood, the nozzle shouldn't go down before printing because its already at Z home. But somehow it overrides the Z end stop signal and touches the bed.

I have also uploaded a video here [youtu.be] (make sure annotations are enabled while watching).

Please help, thanks.

Hi, a possibility would be a line in your slicer start up g-code. Look for a nozzle lift command and remove it. Oddly enough it doesn't lift but causes the nozzle to override the end stop

What firmware are you using?

I had a similar problem with Repetier until I reflashed it...

Also try a different slicer...

---

Self-sourced Mendelmax 2.0-based Reprap Machine -- Ramps 1.4 & Mega 2560 -- DRV8825 (Z@1A, [email protected], [email protected], E@1A) -- genuine E3D v6 direct setup -- 350W custom silicone heated bed -- ABS 1,75mm -- Marlin 1.1.0-RC7 -- Cura 15.04.6

@ShankMan: There's no such line. I have attached an image of G-code. Please have a look.

@Icefire: I am using Marlin firmware. I am using Cura, I tried doing it with repetier, but I was facing another problem with that. The extruder was going up before print and was extruding atleast 50 mm away from the bed.

Check the firmware has the z stops set as hard stops - you should not be able to go past these.
Check you have the correct machine selected in the software your last attachment mentions moving the bed lower. I don't know if that is a generic term used incorrectly but clearly your bed doesn't move so it will be an issue.

@MCcarman: It was working perfectly, then suddenly 2-3 days back this problem started occurring. I haven't touched the firmware. It was pre-installed by the seller. I have tried it with Cura and repetier, both are giving me same problems.

Slic3r used to include this automatically in the startup code.



get rid of the nozzle lift line if you have it. all it did was cause the nozzle over ride the limit switch and plunge into the bed

look at your firmware settings to verify the min and max end stop settings are defined

#define min_software_endstops true // If true, axis won't move to coordinates less than HOME_POS.
#define max_software_endstops true // If true, axis won't move to coordinates greater than the defined lengths below.

// Travel limits after homing
#define X_MAX_POS 160
#define X_MIN_POS 0
#define Y_MAX_POS 155
#define Y_MIN_POS 0
#define Z_MAX_POS 95
#define Z_MIN_POS 0

If your printer homes correctly and the problem starts only after you start printing than there is a problem with your
slicer generated g-codes. open up the g-code in a text editor and locate the line thats telling your nozzle to drop
below 0 or your first layer height.

here is a snippet of some start up g-code


; generated by Slic3r 1.1.7 on 2017-02-05 at 14:34:09

; perimeters extrusion width = 0.25mm
; infill extrusion width = 0.35mm
; solid infill extrusion width = 0.35mm
; top infill extrusion width = 0.35mm

G21 ; set units to millimeters
M106 S0
G28 ; home all axes


G90 ; use absolute coordinates
G92 E0
M82 ; use absolute distances for extrusion
G1 F1800.000 E-1.00000
G1 Z1.150 F7800.000
G92 E0
G1 X30.237 Y30.893 Z1.150 F7800.000 ( check to see if Z is a negative number like Z-1.50)
G1 Z0.150 F7800.000
G1 E1.00000 F1800.000
G1 X31.973 Y29.487 E1.04030 F1080.000

Check your z-offset value.
Every so often I have to reset mine (strange behaviour, i know)