This problem only affects prints taller than 268mm when printing with materials that require the chamber heater to be enabled.
The hot air exhaust of the chamber heater exits into the main chamber towards the very bottom of the left side of the chamber.
Unfortunately the print bed, when at Z heights of 268mm and greater will increasingly block off the chamber heater's outlet when the heater is active. This can lead to a thermal event being triggered by Klipper, resulting in Klipper shutting the firmware down immediately and ruining any print in progress.
A true fix for this issue would require Qidi to come up with a hardware fix that does not result in the print bed blocking the outlet of the chamber heater when the print bed is near the very bottom of the chamber.
NOTE: While the following does not fix the fundamental hardware flaw in the printer's design, it does essentially nullify its impact.
The following configuration will disable the chamber heater's coils whenever the print bed is at a Z height of 268mm or greater. The idea here is to disable the heater coils and then complete the remainder of the print using the latent heat within the chamber and by making best possible use of the heating element of the print bed. This will mitigate the firmware shutdown issue and, in almost all reasonable scenarios, will allow the print to complete successfully.
Within the gcode-macro.cfg file we can add in the following macro:
[gcode_macro SET_PRINT_STATS_INFO]
rename_existing: SET_PRINT_STATS_INFO_BASE
gcode:
{% set curlayer = params.CURRENT_LAYER|default(1)|int %}
{% if (printer.toolhead.position.z) >= 268 %}
# Set chamber target to 10C, which still keeps the chamber heater fan on
# This allows the print bed to warm the chamber more effectively even
# though the heater coils are effectively disabled
M141 S10
{% endif %}
SET_PRINT_STATS_INFO_BASE CURRENT_LAYER={curlayer}
This will call the macro upon every layer change (as this command is called on every layer change in all stock printing profiles). When the Z height exceeds 268mm, the chamber heater target will be set to 10C.
The target of 10C is important here, instead of using a 0C target.
Using a 10C target will keep the chamber heater's fan spinning, which will still help to circulate some air under the print bed, and this will in turn help to keep the chamber warm as the print bed warms the air-flow under it.
Doing this will prevent the chance for a thermal shutdown event being triggered by the chamber heater, and will keep the chamber warm for the remainder of the print.
The v1.6.0 firmware introduces a new field called target_min_temp to the [heater_generic chamber] config section. The above
macro conflicts with this new field unless target_min_temp is set to 10
For example:
[heater_generic chamber]
heater_pin:U_1:PC8
max_power:0.4
sensor_type:NTC 100K MGB18-104F39050L32
sensor_pin:U_1:PA1
control = pid
pid_Kp=63.418
pid_Ki=1.342
pid_Kd=749.125
min_temp:-100
max_temp:70
target_min_temp: 10 #<--- Ensure that this field is set to 10C (default is 45C)
target_max_temp:65
heat_with_heater_bed:True
heat_with_heater_bed_tem_add:25
In addtion, for added safety the chamber heater fan can be set to run even if the printer does shut down due to the chamber heater overheating.
This can be done by modifying the following in printer.cfg:
[chamber_fan chamber_fan]
shutdown_speed: 1
Qidi's stock PWM power setting for the chamber heater for Firmware versions 1.4.2 and earlier is too aggressive and has been known to cause the Chamber Thermal Protection Sensor to trip. This has been seen to result in a firmware shutdown even in normal operation when a print is first starting to warm the chamber up.
Making the following config change will prevent this from happening.
Additionally, setting a lower max_power value here will also help protect the SSR unit from potentially failing in 110VAC countries as reports
of this for the first batch of Plus4 printers have started to surface somewhat frequently within the first month of customer use.
Find the [heater_generic chamber] section within the printer.cfg file, and then find the line starting with max_power, and set its value to 0.4.
For example:
[heater_generic chamber]
max_power:0.7
Should be replaced with:
[heater_generic chamber]
max_power: 0.4
Note that while the chamber will take a little longer to reach a target temperature, it should still reach the target temperature before the print bed reaches it own target in almost all reasonable scenarios.
Additional note!!!
This should actually be standard from Qidi, but it's not:
Within the G29 macro, which is normally located in the gcode_macro.cfg file, find that macro, and change the M141 S0 portion
at the start of the macro to the following:
[gcode_macro G29]
variable_k:1
gcode:
{% set temp = printer["heater_generic chamber"].target %}
M141 S0
{% if temp > 0 %} # ADD THESE
G4 P15000 # 3 EXTRA
{% endif %} # LINES HERE
BED_MESH_CLEAR
... # Rest of macro continues as before
This will ensure that the chamber fan will stay on for at least 15 seconds longer to allow for the heater unit
to cool down a little more before get_zoffset turns the chamber fan off with TOGGLE_CHAMBER_FAN after G28 is called.
Ideally, Qidi should not be disabling the chamber fan on a potentially hot heater unit, so this is the best we can do in the meantime until they fix this bit of ugliness.