Prusa Silcer Starting Gcode M221 Question
Hello Everyone,
I am confuse about M221 in the start gcode found in Prusa Slicer. (See gcode highlighted in red)
M115 U3.7.2 ; tell printer latest fw version
G90 ; use absolute coordinates
M83 ; extruder relative mode
M104 S[first_layer_temperature] ; set extruder temp
M140 S[first_layer_bed_temperature] ; set bed temp
M190 S[first_layer_bed_temperature] ; wait for bed temp
M109 S[first_layer_temperature] ; wait for extruder temp
G28 W ; home all without mesh bed level
G80 ; mesh bed leveling
G1 Y-3.0 F1000.0 ; go outside print area
G92 E0.0
G1 X60.0 E9.0 F1000.0 ; intro line
G1 X100.0 E12.5 F1000.0 ; intro line
G92 E0.0
M221 S{if layer_height<0.075}100{else}95{endif}
Does this mean if my layer height is set smaller then 0.075, my flow rate will be set at 100%, otherwise it will be reduce to 95%?
If this is the case, then I am very confused because all layer height i use is will be higher then 0.075mm then this line of gcode will effective underextrude all my layer. Since the flow rate will reduce to 95%
Typically, I want the first layer not to under to extrude and to have a 200% extrusion width right?
If someone can explain a bit more about it I will be greatly appreciated.
Thank you in advance.
RE: Prusa Silcer Starting Gcode M221 Question
I think it's more like a "little bit of under extrusion" helps the over all print quality. But at low layer heights (and the very low flow rates they imply), the trade-off is full extrusion is more helpful to keep filament flowing well than any slight under extrusion for appearances.
Add a semi-colon in front of the line before producing gcode, test it. See what happens on your printer.
And no - you do not want layer 1 to be 200% wider than the other layers. In general, you want the same basic extrusion width everywhere. Other printers, ones without PEI heated sheets, need to lay down silly wide thick layer ones to glue the part down. The Prusa doesn't need to do this.
RE: Prusa Silcer Starting Gcode M221 Question
Deep in the forum history there's a post in which JP himself is describing issues with (then) Slic3r over-extruding at larger layer heights. The explanation I last saw explained this as a work-around fix. I have actually gone with reducing the extrusion factor to 0.90 when printing at layer heights over 0.32mm which is where I see the problem. That said, I don't print at layer heights below 0.10mm often.
I wouldn't over-extrude your 1st layer. That sounds a bit like how Simplify 3D handles it, which is one of the reasons I quit using it. As Tim notes, just comment the line out if it causes any confusion.
RE: Prusa Silcer Starting Gcode M221 Question
Thank you Bobstro and Tim taking the time to answer my question and for the explaination 🙂
I will try to comment the line out and see what happens.
RE: Prusa Silcer Starting Gcode M221 Question
I have found that, as supplied by Prusa, I need the extrusion rate to be 95% to get accurate extrusion. That is, if the Gcode says to extrude 1mm of filament, I'll get more than that unless M221 S95 is used. With very small layer heights there is probably more back-pressure reducing flow, so S100 helps there.
Do your own extruder calibration and see what works for you. I followed the steps in https://mattshub.com/2017/04/19/extruder-calibration/ but the process is fairly generic.
RE: Prusa Silcer Starting Gcode M221 Question
[...] Do your own extruder calibration and see what works for you. I followed the steps in https://mattshub.com/2017/04/19/extruder-calibration/ but the process is fairly generic.
What did you wind up with? I went through the process and the result was within 0.02 of the default 280 (IIRC). I've since read that this isn't really necessary in a printer with consistently built designs ... sort of like Apple computers not having variation.
RE: Prusa Silcer Starting Gcode M221 Question
I ended up with 94.8% which is close enough to 95 as to not matter. I had been having some overextrusion issues which I eventually tracked down to my commenting out that M221 line in the start Gcode!
RE: Prusa Silcer Starting Gcode M221 Question
I ended up with 94.8% which is close enough to 95 as to not matter.
My value came out very close as well, so I didn't bother. Fortunately I'd only taken it so far as including a line of gcode with the new value, so backing out was painless.
I had been having some overextrusion issues which I eventually tracked down to my commenting out that M221 line in the start Gcode!
Heh. I left that M221 out just to be avoid surprises. I find I have over-extrusion with layer heights over 0.32, but below that my filament calibration seems to have taken care of it for lower layer heights. I've recently done some 0.04mm and lower tests and didn't have to adjust for the lower heights.
The other thing I started doing was resetting speeds and extrusion multiplier and anything else that might possibly get changed at the start of each job. I got burned a couple of times with prints made after I did some tweaking from the front panel.
RE: Prusa Silcer Starting Gcode M221 Question
At low layer heights (and the very low flow rates they imply), the trade-off is full extrusion is more helpful to keep filament flowing well than any slight under extrusion for appearances.
Add a semi-colon in front of the line before producing gcode, test it. See what happens on your printer.
And no - you do not want layer 1 to be 200% wider than the other layers. In general, you want the same basic extrusion width everywhere.
RE: Prusa Silcer Starting Gcode M221 Question
At low layer heights (and the very low flow rates they imply), the trade-off is full extrusion is more helpful to keep filament flowing well than any slight under extrusion for appearances.
Add a semi-colon in front of the line before producing gcode, test it. See what happens on your printer.
And no - you do not want layer 1 to be 200% wider than the other layers. In general, you want the same basic extrusion width everywhere.
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RE: Prusa Silcer Starting Gcode M221 Question
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RE: Prusa Silcer Starting Gcode M221 Question
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RE: Prusa Silcer Starting Gcode M221 Question
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RE: Prusa Silcer Starting Gcode M221 Question
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