Modifying Start Gcode To Prime A Line?

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Modifying Start Gcode To Prime A Line?

Postby novice » 2018-Apr-Wed-13-Apr

The ultimate goal is to prime a line across the front of the bed on the X axis of a Simple Metal prior to printing, similar to the Simple Pro routine. Looking at the Marlin Wiki causes me to realize my understanding of the change required is to put it kindly, limited. Could someone recommend modification to accomplish that?

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
G29 ;Run the auto bed leveling
G1 Z10.0 F{travel_speed} ;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 F{travel_speed}
;Put printing message on LCD screen
M117 Printing...
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Modifying Start Gcode To Prime A Line?

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Re: Modifying Start Gcode To Prime A Line?

Postby Mooselake » 2018-Apr-Wed-14-Apr

That's pretty much what I've done for years...

I'd suggest moving to a bit higher Z, and extrude more like 10mm instead of 3. The extra room gives you some space to grab the extrusion so it doesn't get hauled around the bed, and the extra 7mm will do a better prime. Also, the speeds in gcode are mm per minute so you might want to revisit them. Z should be able (off the top of my head, always dangerous) to do 2 or 3 mm/sec so try at least F100 (my allthread Z would do 300, the T8-8 mod 1200 mm/min), and 3mm/sec (around 200/60) seems really slow for an extruder. I'd boost that by at least a factor of 5, then experiment by increasing the speed to see how fast it'll go. Your maximum speeds are set in EEPROM, and will be limited to the configured maximum. It's likely those are quite conservative, but that's another topic.

i thought I'd posted my start gcode here in the past (it's a bit more elaborate), but either the search-fu is weak or I haven't. Unfortunately I'm not at the computer that has it.

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Re: Modifying Start Gcode To Prime A Line?

Postby RetireeJay » 2018-Apr-Wed-15-Apr

For starters, you won't be able to extrude anything until you heat up the extruder. You would have to insert that command somewhere before the command to do any extruder motion. You would use M109 in order to force the 'bot to wait until reaching setpoint heat before going on to the next steps. For example, "M109 S200"

novice wrote:The ultimate goal is to prime a line across the front of the bed on the X axis of a Simple Metal prior to printing

Does that mean you want to actually print a line on the bed across the bed? It may be a better option just to specify a "skirt" in your slicer, which will print one or more loops around your model before starting to print the part itself. Or, as seems to be implied by the discussion above, do you simply want to fill the extruder hot zone so that it's ready to print?

I actually do most of those things "manually". I click home buttons to zero X, Y, and Z, then raise Z 20mm, then heat the extruder. When the extruder reaches final temperature, I click the "extrude 10mm" button twice, then (while it's still extruding) I click the "print" button. While the extrusion is happening, I reach in with a pair of pliers and grab the filament coming out, pulling it off to the side at just the right rate so it doesn't break but doesn't fall onto the bed. When the final 10mm is finished extruding, the print starts with the nozzle moving down to print level and them moving to the correct X, Y coordinate. In spite of this "priming" manually, I also use a skirt to make absolutely sure that the extruder chamber is full and pressurized.

By the way, the commented line "G1 Z10.0 F{travel_speed} ;move the platform down 15mm" holds a couple of gotchas for the reader. First, and this may be obvious, the "travel_speed" inside curly brackets is referring to a variable that must have been established somewhere before the parser reaches this line. If you are writing this yourself, you would put in a number, e.g. "G1 Z10.0 F300". Second, the comment "move the platform down 15mm" refers to a printer with a different mechanism than our Printrbot. All Printrbots move the printhead UP, not the platform down, when moving to a Z value greater (more positive) than it is a present.
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Re: Modifying Start Gcode To Prime A Line?

Postby Mooselake » 2018-Apr-Thu-14-Apr

Repetier-Host will preheat the bed and extruder if you don't add explicit gcode. I think Cura does the same but don't have a way to verify it handy.
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Re: Modifying Start Gcode To Prime A Line?

Postby novice » 2018-Apr-Thu-20-Apr

Mooselake wrote:Repetier-Host will preheat the bed and extruder if you don't add explicit gcode. I think Cura does the same but don't have a way to verify it handy.


Cura 15.04.06 rev. has preheating and that has always been my method of printing.
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Re: Modifying Start Gcode To Prime A Line?

Postby RetireeJay » 2018-Apr-Thu-21-Apr

Are you saying they preheat without your giving a manual command to heat up AND without your hitting the "PRINT" button? I doubt it. What would trigger the preheating? Surely it doesn't start preheating just because you connected.

Here's the thing: almost all slicers will embed the M109 command in the startup code automatically - unless you go to great lengths to prevent that - so "preheating" is not a function of Repetier or Cura per se (the User Interface), but it is a function of the slicer. When you hit "PRINT" then the gcode starts running, and the printer pauses when it hits the M109 command until the extruder has reached temperature.

Come on, guys, recognize that the slicer is not the same thing as the User Interface! Repetier gives you a selection of slicers; Cura gives you only its own slicer, but in either case, the slicer is really a separate piece of software that can be run independently of the User Interface part of Repetier or Cura. And it's very advantageous to do so, IMHO! I NEVER run Slic3r from within Repetier; I ALWAYS slice first and then load the gcode into Repetier. It gives me much more control over the whole process.
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Printrbot Plus operational January 2013
Brass threaded rods (5/16" X 18) & nuts for Z axis
GT2 belts & pulleys
Cable chain to reduce probability of fatigue failure in wires
E3D V5 Hot End, 0.4mm nozzle, also 0.8 and 0.25 in use occasionally
PB fan mount + 40mm fan -- using printed mount adapter, not the E3D supplied fan
Injection molded extruder gears
Optical Z "endstop" (custom designed and built)
Have used many pounds of T-Glase filament. Now also doing some work with Ninjaflex SemiFlex
Print on glass with Scotch Craft Stick or other glue stick
"My next printer is..." Prusa i3 MK3
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Re: Modifying Start Gcode To Prime A Line?

Postby Mooselake » 2018-Apr-Sun-13-Apr

I meant to say that slic3r will insert the missing heater gcode commands, somehow that became mentally abbreviated to r-h and preheat. I plead haste and old-timers
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Re: Modifying Start Gcode To Prime A Line?

Postby Flordonwrath » 2018-Apr-Sat-09-Apr

RetireeJay wrote:Are you saying they preheat without your giving a manual command to heat up AND without your hitting the "PRINT" button? I doubt it. What would trigger the preheating? Surely it doesn't start preheating just because you connected.

Here's the thing: almost all slicers will embed the M109 command in the startup code automatically - unless you go to great lengths to prevent that - so "preheating" is not a function of Repetier or Cura per se (the User Interface), but it is a function of the slicer. When you hit "PRINT" then the gcode starts running, and the printer pauses when it hits the M109 command until the extruder has reached temperature.

Come on, guys, recognize that the slicer is not the same thing as the User Interface! Repetier gives you a selection of slicers; Cura gives you only its own slicer, but in either case, the slicer is really a separate piece of software that can be run independently of the User Interface part of Repetier or Cura. And it's very advantageous to do so, IMHO! I NEVER run Slic3r from within Repetier; I ALWAYS slice first and then load the gcode into Repetier. It gives me much more control over the whole process.
I've noticed frokm playing around with different software that in Cura, you do not have to pre-heat before hitting the print command, once you start the print it goes by whatever settings had been set prior.

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