Nozzle drops (and tracks) ~10C during print
I've noticed after about 20 minutes my nozzle temperature drops 10°C below the target temperature. It fluctuates ±2°C around that point. Sometimes the nozzle temperature will return to matching the target with no intervention.
I tried turning the cooling fan down but that did not change the behavior.
If I increase the temperature, the 10°C differential remains. For example: set to 240C, the nozzle stays around 230C. If I change to 245C while printing, the nozzle quickly reaches 235 and stays around there. If I set target to 250, the nozzle reaches 240 without an issue. So that rules out being unable to reach the target. It is possible, but for some reason the controller is keeping it below target.
I noticed this while printing with Octoprint on firmware 3.2.1-576.
What are reasons that the printer's PID will decide to keep temperature 10degrees lower than either the gcode or the tuning overrides?
Edit: Updated Title
Re: Nozzle drops ~10C during print
To start, i would run the PID configuration. Use the temperature you usually print and turn fan at 50% speed if you use one to print. I've seen temperature drops like this when fan kicks on the full speed and PID was out of range.
Re: Nozzle drops ~10C during print
I once had similar to what the OP is observing, and the problem turned out to be a hole that the hot-end had melted into the blower shroud, resulting in most of the blown air being blown against the hot end. So, maybe worth a look? I printed a new (different) blower shroud, and the problem immediately went away after installing it.
You can also install a sock on the hotend.
Re: Nozzle drops ~10C during print
Update, it is possible to "fix." Going from Normal -> Stealth, the temperature nozzle temp starts tracking the target temperature again. I'm in the middle of a long print and it tracked for several hours.
It looks like a bug in the PID causes an incorrect target. Something about Normal -> Stealth or Stealth -> Normal resets it.
Edit: Update2: Maybe this change does not help. This time I switched back and forth a few times before the temp started tracking again. It was not an instant tracking change. However, there does seem to be correlation.
Re: Nozzle drops ~10C during print
Update, it is possible to "fix." Going from Normal -> Stealth, the temperature nozzle temp starts tracking the target temperature again. I'm in the middle of a long print and it tracked for several hours.
It looks like a bug in the PID causes an incorrect target. Something about Normal -> Stealth or Stealth -> Normal resets it.
I had the same issue. Target was 235 and temp was stuck at 225. Bumped the target to 240, and it stayed at 230. Bumped the target to 250 and it went to 240. When I returned to the printer half an hour later the nozzle was at the target 250. I didn't change anything other than the target before leaving. I'm not sure why it was stuck 10º below target consistently.
Re: Nozzle drops (and tracks) ~10C during print
I had this happen to me once a couple of weeks ago. Identical problem: 10°C under target, regardless of what said target was set to. When I went to start my next print later on it held the nozzle temperature at the target temperature without fault. It hasn't happened before or since then.
I ended up upgrading to 3.2.0 sometime around when that happened, but I can't remember if I did that before or after the incident.
Re: Nozzle drops (and tracks) ~10C during print
I took Octoprint out of the picture. Prints still continue to drop ~10C approximately 10 minutes into the print, based on just watching the LCD. Switching in and out of stealth mode eventually allows the nozzle temp to track.
Re: Nozzle drops (and tracks) ~10C during print
I have seen this behavior from time to time. I have yet to find a cause- but it sure is unnerving. It suggests the firmware has a potentially nasty bug (like overwriting memory somewhere).
Re: Nozzle drops (and tracks) ~10C during print
Considering it seems to be a consistent 10°C drop I'm not sure that it's quite that severe. My guess would be that there's some sort of logic bug that's causing the heater temperature to get adjusted as it's heating (or, alternatively, when it's being reported to the LCD and serial port—do we know for sure that the hot end temperature is actually dropping?).
10 is just an odd number for it to off by. It's not a power of two and doesn't seem to be the result of a flipped bit so it's doubtful that it's a bitwise operation gone wrong, it's not a doubled or halved value so it's not an accidental bit shift, and it's a consistent offset across multiple printers.
What firmware is everyone running? Does this happen with all gcode that you feed to the printer or does it happen across the board?
Re: Nozzle drops (and tracks) ~10C during print
I have this problem. It just started happening on a larger print with large base. It's PETG temp set to 240 and it is riding at 230-231. I tried the Stealth/Normal trick with no luck. Tuning temp higher didn't change it from the 230 area. It's a MK3.
Re: Nozzle drops (and tracks) ~10C during print
The same problem is happening on my newly build (day 2, print no 4) at the moment. Consistent drop of 10 C while printing a larger (12x15 cm) print. Happened when the third layer started printing. Print is being done using Octoprint.
Firmware is 3.3.1. Printing with FormFutura Stonefil PLA.
Re: Nozzle drops (and tracks) ~10C during print
In all this discussion I've not seen anyone talk about the end result, you know, the print. 😆
What do the prints look like when this supposed drop takes place?