What setting did I change to make Cura add "G1 F600 Z1.2" as the first move?

[racketteer 0]

Hi,

 

I am using Cura 4.8. I have a delta printer, so the first hotend movement command usually brings the nozzle down from Z270 to Z0.2 or whatever my first layer will be.

 

I have been experimenting with some settings to try to improve the print. One of the settings changed the initial move. It now adds "G1 F600 Z1.2."

 

It used to be:

;LAYER_COUNT:226
;LAYER:0
M107
G0 F5400 X16.135 Y-17.736 Z0.2
;TYPE:SKIRT
G1 F2400 E0

 

But now it is

;LAYER_COUNT:226
;LAYER:0
M107
G1 F600 Z1.2
G0 F5400 X16.135 Y-17.736 Z0.2
;TYPE:SKIRT
G1 F2400 E0

 

What setting made this happen?

 

Thanks,

Daniel

 

[gr5 2,099]

I'm thinking "z hop when retracted"

[racketteer 0]

Thank you! This was it. Since nothing is printed yet I am surprised that the z hop would get triggered, but I'm pretty new to 3D printing. I appreciate your quick response. I'll go and play some more.

Daniel

[gr5 2,099]

It could also be related to "retract on layer change".  Since going to the very first layer is sort of a layer change it might retract.  And whenever it retracts it hops.

 

"z hop when retracted" is a really bad idea for 90% of printers but works great for Delta printers like yours.

 

retracting on layer change - probably not a good idea.

[racketteer 0]

Thank you for the additional suggestion. The gcode does not show a retraction before that first move. I have coded an initial extrusion as part of the initial sequence, but that is extrusion, not retraction.

 

When I turned off z hop but left all other settings alone, the offending line went away. I'm puzzled, but now that I know its origin I can work with it, experiment with some of the related z hop settings, etc.

[gr5 2,099]

Well cura almost likely considers the start of your print an "unretraction".  The moment before it starts printing.  So it probably feels it also has to do an "unhop". 

 

It also considers the first layer a "layer change".  Most likely.  Just guessing here (trying to think like the programmer who wrote these features).

 

[racketteer 0]

Actually, it seems to be a known, open bug, if I am interpreting github correctly. https://github.com/Ultimaker/Cura/issues/7382

 

Is it recommended for me to add my experience to that thread, or leave it alone (if I even have the necessary permissions)? Or maybe you can point me to the “rules” for submitting issues to the sw?

 

 

[gr5 2,099]

I guess I don't understand why you care.  On the way to printing at z=0.2 it pauses for just an instant at Z=1.2.  Why is this a problem?

[racketteer 0]

The issue isn’t the momentary pause at Z1.2, it is the speed F600 instead of F5400 (or max speed of config.h).
 

Instead of zipping down from Z275 to Z1.2 at speed F5400, it slowly moves down the center of the bed at speed F600. The extra 10 seconds or so also wouldn’t be too bad except the nozzle oozes filament on the way down (I have a priming extrusion as part of the start up). If the effector moves quickly to the first print location, the ooze becomes part of the brim. Also, I can easily “wipe its nose” on the way to the starting location. When the effector drops that slowly down the center, the ooze makes a puddle of filament in the very center of the bed where the print will be the entire way down, before it finally moves quickly to the first X,Y location.

[GregValiant 1,146]

Can you add a couple lines to the end of your start gcode like maybe:

G1 F{machine_max_feedrate_x} X-100 Y0   ;move to far left

G1 F{machine_max_feedrate_z} Z1.2     ;move down

that would move the head out of the center and then drop the head at the faster rate.

 

I have a similar situation but it's a retraction that Cura adds "G1 F1800 E-6".  I use the Search and Replace plugin to change that line to G92 E-4 and any skirt or brim now starts correctly.  That trick only works because the "search" line only appears once in the gcode.  Your line might appear multiple times and they would all be replaced.

[racketteer 0]

That's a clever workaround. I have been editing the gcode in Notepad++ to delete the line. It is right near the top of the file and very easy to find. Adding a fast move to Z1.2 in the startup means I wouldn't have to postprocess by hand. Thank you for the suggestion.

[GregValiant 1,146]

Your welcome.

What's your useable build plate diameter?