Nozzle starts printing with temp not yet achieved

Bambu Lab H2 Series
1

I would not find this issue unless trying printing the transparent object.

If I print just thin cube (2 lines thick) with transparent MABS standing vertically in the plate, it prints very well.

But as soon as I put this cube as a window into the bigger part, printing MABS with one nozzle and ABS with another nozzle, the quality if window is awful, it puts balls of air inside and in general has defective surface.

I noticed that as printer starts switching the nozzle, it stops heating the nozzle being changed (demoted). That would be totally understandable and ok, but the nozzle which is being promoted into operation is cooled down when process starts, and while printer does specific tasks on printing tower before approaching the part to print, it comes to the part with temp up to 10 C less than minimal allowed. I’d expect printer to wait until nozzle heats to nominal temp and temp stabilizes, and only then starts touching the part.

AI proposes to dig into filament properties or slicer state machine disabling G codes but I think it is totally wrong. There must be an option to instruct printer to sacrifice speed and favor the quality and wait until nozzle heats and only then start printing.

Please advise. Thanks.

2

It would help to know what printer you’re using.

Generally, though, this isn’t done by accident, I suspect what’s really happening here is a method to avoid nozzle ooze, so heating is being timed to just get up to temp as the print begins. Keep in mind, the onscreen temperature you’re seeing is delayed as nozzle temp only refreshes every ~1 second.

And 10 degrees below the minimum temperature is nothing. It’s still going to be well above the glass transition temperature for all common filaments.

3

Thanks.

Is there any proof for this? That printing actually really begins when temp is the one set for filament AND this temp is proven to be stabilized? I’d love to see the implemented algorithm for it and possibilities for tuning.

When printing transparent object this is not true. +10 C will lead to darker/smoked internals. Proven by my experience. -10 C may lead to worse adhesion of the nearby plastic, less gas mobility and thus bubbles in the layers. When printing without nozzle operation interruptions the adverse effect is missing.

4

These are the controls for [not/blocking] till nozzle temp achieved
https://marlinfw.org/docs/gcode/M104.html
https://marlinfw.org/docs/gcode/M109.html

If it’s as critical as you claim, give it the ol’ m109 and/or make it sleep for a second afterwards

5

Yes, it does, and the inertia causes the temperature to overshoot the set point by up to 5°C. Then it cuts off to cool down, only to overshoot the set temperature again. It goes up, then down again, and after a few oscillations, it finally stabilizes. It didn’t used to do this, it used to reach the perfect temperature right away on the first layer tower. Now, however, I’m finding pieces of plastic on the print bed. I’m exhausted.

6

This is what I wanted to avoid. Manual editing of the printer machine g-code. First of all, I am not sure how to do it. E.g. start code has section

;===== nozzle load line ===============================
    G29.2 S1 ; ensure z comp turn on
    G90
    M83
    G1 Z5 F1200
    G1 X270 Y-0.5 F60000
    G28.14 R0
    G29.2 S0
    G91
    G1 Z0.8 F1200
    G90
    G1 X250 F60000
    M109 S{nozzle_temperature_initial_layer[initial_no_support_extruder]}
    M83
{if (filament_type[initial_no_support_extruder] == "TPU")}
    G1 E5 F{filament_max_volumetric_speed[initial_no_support_extruder]/2.4053*60}
{endif}
    G1 E5 F{filament_max_volumetric_speed[initial_no_support_extruder]/2.4053*60}
    G1 X290 E10 F{filament_max_volumetric_speed[initial_no_support_extruder]/2.4053*60}
    G91
    G3 Z0.4 I1.217 J0 P1 F60000
    G90
    M83
    G29.2 S1 ; ensure z comp turn on
;===== noozle load line end ===========================

seems to be the section to deal with, BUT “noozle” at the end of the section confuses me - ok if it just a comment, not ok if it somehow used to identify blocks of the code.

This is clear that nozzle’s temp is not a perfect constant, and it will be fluctuating a little. I need printer to ensure that, before proceeding to **wipe tower** and then to the part, it waits for nozzle to reach temp, and have it stabilized for some time (have no significant temp overshoot).

Alternatively, I think it would be acceptable for printer NOT to cool down the nozzles at all putting over-heated plastic onto the wipe tower before going to the part.

Update: here’s the code from “change filament” section

;======== H2D ========
;===== 20260116 =====
M993 A2 B2 C2 ; nozzle cam detection allow status save.
M993 A0 B0 C0 ; nozzle cam detection not allowed.

{if (filament_type[next_extruder] == "PLA") ||  (filament_type[next_extruder] == "PETG")
 ||  (filament_type[next_extruder] == "PLA-CF")  ||  (filament_type[next_extruder] == "PETG-CF")}
M1015.4 S1 K0 ;disable E air printing detect
{else}
M1015.4 S0 ; disable E air printing detect
{endif}

M620 S[next_extruder]A
M1002 gcode_claim_action : 4
M204 S9000

G1 Z{max_layer_z + 3.0} F1200

M400
M106 P1 S0
M106 P2 S0

{if toolchange_count == 2}
; get travel path for change filament
;M620.1 X[travel_point_1_x] Y[travel_point_1_y] F21000 P0
;M620.1 X[travel_point_2_x] Y[travel_point_2_y] F21000 P1
;M620.1 X[travel_point_3_x] Y[travel_point_3_y] F21000 P2
{endif}

{if ((filament_type[current_extruder] == "PLA") || (filament_type[current_extruder] == "PLA-CF") || (filament_type[current_extruder] == "PETG")) && (nozzle_diameter[current_extruder] == 0.2)}
M620.10 A0 F74.8347 L[flush_length] H{nozzle_diameter[current_extruder]} T{flush_temperatures[current_extruder]} P[old_filament_temp] S1
{else}
M620.10 A0 F{flush_volumetric_speeds[current_extruder]/2.4053*60*0.8} L[flush_length] H{nozzle_diameter[current_extruder]} T{flush_temperatures[current_extruder]} P[old_filament_temp] S1
{endif}

{if ((filament_type[next_extruder] == "PLA") || (filament_type[next_extruder] == "PLA-CF") || (filament_type[next_extruder] == "PETG")) && (nozzle_diameter[next_extruder] == 0.2)}
M620.10 A1 F74.8347 L[flush_length] H{nozzle_diameter[next_extruder]} T{flush_temperatures[next_extruder]} P[new_filament_temp] S1
{else}
M620.10 A1 F{flush_volumetric_speeds[next_extruder]/2.4053*60*0.8} L[flush_length] H{nozzle_diameter[next_extruder]} T{flush_temperatures[next_extruder]} P[new_filament_temp] S1
{endif}

{if long_retraction_when_cut}
M620.11 P1 I[current_extruder] E-{retraction_distance_when_cut} F{max((flush_volumetric_speeds[current_extruder]/2.4053*60), 200)}
{else}
M620.11 P0 I[current_extruder] E0
{endif}

{if long_retraction_when_ec}
M620.11 K1 I[current_extruder] R{retraction_distance_when_ec} F{max((flush_volumetric_speeds[current_extruder]/2.4053*60), 200)}
{else}
M620.11 K0 I[current_extruder] R0
{endif}

M620.15 C{new_filament_temp - filament_cooling_before_tower[next_extruder]}

M628 S1
{if filament_type[current_extruder] == "TPU"}
M620.11 S0 L0 I[current_extruder] E-{retraction_distances_when_cut[current_extruder]} F{max((flush_volumetric_speeds[current_extruder]/2.4053*60), 200)}
{else}
{if (filament_type[current_extruder] == "PA") || (filament_type[current_extruder] == "PA-GF")}
M620.11 S1 L0 I[current_extruder] R4 D2 E-{retraction_distances_when_cut[current_extruder]} F{max((flush_volumetric_speeds[current_extruder]/2.4053*60), 200)}
{else}
M620.11 S1 L0 I[current_extruder] R10 D8 E-{retraction_distances_when_cut[current_extruder]} F{max((flush_volumetric_speeds[current_extruder]/2.4053*60), 200)}
{endif}
{endif}
M629

{if (filament_type[current_extruder] == "TPU" || filament_type[next_extruder] == "TPU") && (old_extruder_variant != "Direct Drive TPU High Flow")}
M620.11 H2 C331
{else}
M620.11 H0
{endif}

{if  (old_extruder_variant == "Direct Drive TPU High Flow") && (filament_map[current_extruder] == 2) && (filament_map[next_extruder] == 1)}
;debug log pe:{previous_extruder} ce:{current_extruder} ne:{next_extruder} oev: {old_extruder_variant} nev:{new_extruder_variant}
;debug fm-curr:{filament_map[current_extruder]} fm-next:{filament_map[next_extruder]}
;sw from R2L&TPU kit, travel run a distance for sketch TPU
G1 X30 Y30 F5000
M400
G1 X300 Y30 F5000
M400
{endif}

T[next_extruder]

;deretract
{if filament_type[next_extruder] == "TPU"}
{else}
{if (filament_type[next_extruder] == "PA") || (filament_type[next_extruder] == "PA-GF")}
;VG1 E1 F{max(new_filament_e_feedrate, 200)}
;VG1 E1 F{max(new_filament_e_feedrate/2, 100)}
{else}
;VG1 E4 F{max(new_filament_e_feedrate, 200)}
;VG1 E4 F{max(new_filament_e_feedrate/2, 100)}
{endif}
{endif}

; VFLUSH_START

{if flush_length>41.5}
;VG1 E41.5 F{min(old_filament_e_feedrate,new_filament_e_feedrate)}
;VG1 E{flush_length-41.5} F{new_filament_e_feedrate}
{else}
;VG1 E{flush_length} F{min(old_filament_e_feedrate,new_filament_e_feedrate)}
{endif}

SYNC T{ceil(flush_length / 125) * 5}

; VFLUSH_END

M1002 set_filament_type:{filament_type[next_extruder]}

M400
M83
{if next_extruder < 255}

M620.10 R{new_extruder_retracted_length}
M628 S0
;VM109 S[new_filament_temp]
M629
M400

;prime_tower_interface
{if is_prime_tower_interface && filament_tower_interface_purge_volume !=0}
G150.1
M620.13 W0 L{filament_tower_interface_purge_volume} T{filament_tower_interface_print_temp} R0.0
{endif}
;prime_tower_interface

M983.3 F{filament_max_volumetric_speed[next_extruder]/2.4} A0.4 R{new_extruder_retracted_length}

M400
{if wipe_avoid_perimeter}
G1 Y320 F30000
G1 X{wipe_avoid_pos_x} F30000
{endif}
G1 Y295 F30000
G1 Y265 F18000
G1 Z{max_layer_z + 3.0} F3000
{if layer_z <= (initial_layer_print_height + 0.001)}
M204 S[initial_layer_acceleration]
{else}
M204 S[default_acceleration]
{endif}
{else}
G1 X[x_after_toolchange] Y[y_after_toolchange] Z[z_after_toolchange] F12000
{endif}
M621 S[next_extruder]A

M993 A3 B3 C3 ; nozzle cam detection allow status restore.

{if (filament_type[next_extruder]  == "TPU")}
M1015.3 S1;enable tpu clog detect
{else}
M1015.3 S0;disable tpu clog detect
{endif}

{if (filament_type[next_extruder] == "PLA") ||  (filament_type[next_extruder] == "PETG")
 ||  (filament_type[next_extruder] == "PLA-CF")  ||  (filament_type[next_extruder] == "PETG-CF")}
M1015.4 S1 K1 H[nozzle_diameter] ;enable E air printing detect
{else}
M1015.4 S0 ; disable E air printing detect
{endif}

M620.6 I[next_extruder] W1 ;enable ams air printing detect
M1002 gcode_claim_action : 0

“;:sob: VM109 S[new_filament_temp]” ???

And I do not see explicit nozzle change section.

7

I added M109 S[new_filament_temp] after this commented line, will post results asap.