[Chiuso] Question about "Preheat" - Bed before Hot End  

RE: Question about "Preheat" - Bed before Hot End

Have a look at my Startup and End G-code which i created just for PETG printing.

The first step is to home the printer so it knows where it is, then I move the print head up and start heating, PETG comes off nicely starting from 90 Deg, and leaves a clean nozzle. At 150 Deg, pressing the control knob will continue to the next step or if left, it will continue on its own after approx 10 seconds.

I preheat the PINDA for most accurate bed levelling, but you can comment this out if you don't like the wait. 

I modded my purge as I found it was just too much and now get much cleaner starts without so much material stuck to the nozzle.

Here is the start and end  G-Code:

START:

M115 U3.5.1 ; tell printer latest fw version
M83 ; extruder relative mode
G28 W ; MUST FIRST home all without mesh bed level or else risk nozzle crash!
G1 X10 Y200 Z110 F1000 ; move print head up to allow nozzle to be cleaned
M104 S150 ; preheat extruder to no ooze temp to help clean deposits
M109 S150 ; wait for extruder temp 
M1 S10 ; Wait approx 10s to allow time to clean nozzle ooze then continue without user intervention.
G0 X70 Y70 Z0.5 F1000; PINDA warms faster near bed 
M140 S[first_layer_bed_temperature] ; set bed temp
M190 S[first_layer_bed_temperature] ; wait for bed temp
M860 S35 ; wait for PINDA temp. For most stable PINDA temp during mesh, set temp here 1-2 deg below your actual PINDA temp at end of mesh cal.
M104 S100 ; drop extruder to lower temp to minimize PINDA temp rise during mesh
G80
G1 Y-3.0 F1000.0 ; go outside print area
G92 E0.0
G1 Z3 ; raise head safely clear of bed before heating extruder
M104 S[first_layer_temperature] ; we heat extruder AFTER mesh to minimize ooze
M109 S[first_layer_temperature] ; wait for extruder temp
G1 Z0.6 ; move slightly above bed for easy clean intro line
G1 E5.0 F1000.0 ; squirt a blob to stick any gossamer threads to the print bed before movement
G1 X60.0 E6.0 F1000.0 ; intro line
G1 X100.0 E9.0 F1000.0 ; intro line
G1 X95.0 E0 F1000.0 ; -5mm intro line @ E0 to wipe other side of nozzle
G1 X100.0 E0 F1000.0 ; +5mm intro line @ E0
G1 Z0 ;lower head back to normal Z after intro line
G92 E0.0
M221 S{if layer_height==0.075}100{else}95{endif}

END:

G1 E-0.6 F2100;Anti stringing retract at end of print
G4 ; wait
M221 S100
M104 S0 ; turn off temperature
M140 S0 ; turn off heatbed
M107 ; turn off fan
{if layer_z < max_print_height}G1 Z{z_offset+min(layer_z+30, max_print_height)}{endif} ; Move print head up
G1 X0 Y200; home X axis
M84 ; disable motors

RE: Question about "Preheat" - Bed before Hot End

Actually - there is no need to wait for the extruder while heating the bed; the bed takes much longer to heat.  And like any good code, startup gcode should be structured and formatted for readability, and commented:

; initial settings
M115 U3.7.1 ; tell printer latest fw version
G90 ; use absolute coordinates
M83 ; extruder relative mode

; preheat things to a low temp, get nozzle plastic mushy before driving into the bed with G28
M140 S[first_layer_bed_temperature] ; set bed temp
M109 S175 ; wait for extruder temp
G28 W ; home all without mesh bed level
M190 S[first_layer_bed_temperature] ; set & wait for bed temp

; soak PINDA then level
G0 X50 Y50 Z1 F3000; this is a good PINDA heating position
M860 S37.5 ; wait until PINDA is >= 35C in winter, 37.5C spring/fall, 40C summer
G80 N7 R5; mesh bed leveling

; heat nozzle to extrude temp
G0 X0 Y-3.0 Z10 F3000; this is a good nozzle heating position
M109 S[first_layer_temperature] ; set & wait extruder temp

; purge
G1 Y-3.0 Z0.15 F1000.0 ; go outside print area
G92 E0.0
G1 X60.0 Z0.3 E9.0 F1000.0 ; intro line
G1 X100.0 Z0.4 E15.0 F1000.0 ; intro line
G1 X90.0 E0.0 F1000.0 ; wipe
G1 X95.0 E0.0 F3000.0 ; wipe
G92 E0.0

G92 E0.0
M221 S{if layer_height<0.075}100{else}95{endif}

; Some other examples
; 
; M104 S ; set extruder temp
; M140 S ; set bed temp

; M109 S ; wait for extruder temp
; M190 S ; wait for bed temp

; layer_height
' layer_z

RE: Question about "Preheat" - Bed before Hot End

Everyday's a school day.

How I missed that I'll never know, make the filament soft before homing! and yes, start the bed heating ASAP. (Thanks Tim)

It's well worth going over your startup G-code after you have been using it for a while as you may well find, there is always room for improvement as well as tidying up the commenting. I had been commenting each line as it makes it easier to cut and paste to create new code, but it is fairly complete how I use it, so adding block commenting like Tim does, is good practice as it allows you to skip over parts quickly and get to just what you may want to change without having to read it all.

RE: Question about "Preheat" - Bed before Hot End

Yeah - my gcode is in constant flux; I'm fighting a purge line stringing problem I have yet to solve.   Trying to do a proper wipe to remove klingons is proving a lot more difficult than I would expect.  where is Captain Kirk when you need him?

RE: Question about "Preheat" - Bed before Hot End

Sorry for the log reply, been a bit under the weather the last couple days.

Thanks everyone for the advice and tips, I will see what I sift thought and see about making the start and end Gcode changes for my prints!!  I just wish they would implement this into the firmware of the machine so that when you choose the material that you're working with from the "Preheat" menu on the printer it would heat the bed first and then start warming the hot end.  I guess I might be the only one that is wondering about this specific feature though, lol!! 😀 

RE: Question about "Preheat" - Bed before Hot End

Posted by: @tim-m30

Yeah - my gcode is in constant flux; I'm fighting a purge line stringing problem I have yet to solve.   Trying to do a proper wipe to remove klingons is proving a lot more difficult than I would expect.  

I do a small retraction before wiping and extend the final wipe action past the end of the prime line (X110). That has eliminated any of the prime line stringing for my prints.

RE: Question about "Preheat" - Bed before Hot End

Posted by: @miserieschild

I guess I might be the only one that is wondering about this specific feature though, lol!!

No, you're not. There are tons of different requirements. That's why this behavior is in gcode and not in the firmware hard coded.

If you print PLA in the regular home temperature environment (50-60C bed, 200-220C nozzle) then it heats up almost at the same time. Only if you go over 60C, the difference is getting bigger. But usually if I print ABS, I want the enclosure to be preheat. Nozzle heat is helping in this process. So my default setting is still Prusa Default, heat up everything at the same time.