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brit

z axis not homing properly

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I have been using Cura for several months with my Creatr printer. It has been fantastic. However when I replaced my Creatr motherboard for some reason the Cura G-code in Repitier –Host caused the z axis to be located higher than it used to be - and higher than it is when homing the Z. It always jogged down a bit then back up at the beginning of a print, but now it jogs too far up ....right into the bed.

So I then bit the bullet and bought Simplify3d. It is OK, but Cura is far better for my imperfect scans and intersecting meshs. Simplify3d has been creating some pretty weird slices with them whereas Cura does a perfect job every time.

How can I solve that jog up and down at the begining of the print so that it will home on the z axis properly? I assume that it has something to do with the G-code - that I could edit out?

Perhaps this: “G1 Z15.0 F5400 ;move the platform down 15mm”?

The beginning of the g-code:

140 S60.000000

G21 ;metric values

G90 ;absolute positioning

M82 ;set extruder to absolute mode

M107 ;start with the fan off

G28 X0 Y0 ;move X/Y to min endstops

G28 Z0 ;move Z to min endstops

G1 Z15.0 F5400 ;move the platform down 15mm

G92 E0 ;zero the extruded length

G1 F200 E3 ;extrude 3mm of feed stock

G92 E0 ;zero the extruded length again

G1 F5400

;Put printing message on LCD screen

M117 Printing...

;Layer count: 450

;LAYER:-2

;RAFT

G0 F5400 X30.00 Y63.05 Z0.30

 

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Cura does 2 assumptions.

a) The firmware homing takes care of setting Z0 = bed touching nozzle

b) The firmware limits the Z speed.

Could be that your firmware of your new board is configured differently then the old board.

 

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I have repetier host but I only use it to look at gcode files visually - I haven't connected it to my printer yet so I am unfamiliar with the interface but I assume it lets you type gcodes in one at a time, right? If not then use the cura print window to do this (with pronterface-like-gui plug in) or get pronterface itself (let me know if you needa link).

Anyway, once you do that, you should type in the "move" related commands to see what is going on exactly. Type them in one at a time and experiment.

These two commands home the axis and I expect it is at the "0,0,0" position afterwards. You only need to do the Z axis homing as that is where your curent problem is.


G28 X0 Y0 ;move X/Y to min endstops
G28 Z0 ;move Z to min endstops

This next command moves the Z axis by 15mm. Is this the problem command? Maybe F5400 is too fast for your printer? That's 5400 mm/ minute (which if you divide by 60 you can get it in mm/sec).


G1 Z15.0 F5400 ;move the platform down 15mm

This last command is where the had and the bed come back together. This is where your problem probably occurs:


G0 F5400 X30.00 Y63.05 Z0.30

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Thank you. I can edit the G-code in the start/end tab. Perhaps I can just delete the line "G1 Z15.0 F{travel_speed} ;move the platform down 15mm"? I'll try it when my 12 hour print is complete, and when I have a chance this weekend. I'll push the hot end up so i don't destroy another nozzle...and hope the bed doesn't break (it has not so far) in case it doesn't work.

 

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Do you really need automated starts? It's really a good thing to watch the first minute of the print as the bottom layer is the most common fail point.

Anyway I would leave the 15mm part - after that it extrudes a bit "E" is extruder. G92 resets the position so that:

G92 E0

Tells the extruder that it is "now at position 0".

Then after the extrusion move over to the side and down to the bed - maybe:

G0 X20 Z0

Then do the wipe

G0 X40 Z0

Then maybe lift slightly

G0 Z1

Then let it move to the start of the skirt/brim/whatever. The Z1 lift is optional but if you don't do the lift it may pull up some tape as it drags over to the start. Maybe Z0.1 instead.

Edit: oops - meant Z0, not Y0. Fixed now.

 

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