Hi everyone! Long time lurker, first time poster. I didn’t want to have to bother anyone with this issue, but since Aelph Objects support has been terrible lately (due to moving locations) I can’t rely on them.
The Machine:
I have a Taz 5 with the single v2 extruder. Nothing fancy
The Issue:
For almost a year now I’ve been combating under extrusion and didn’t figure out why until a few months ago. When my extruder temp is set to 205° for PLA (either set in cura, or octoprint, or at the machine itself), all signs point to it having heated up to 205° but when I take a Fluke thermometer with a thermocouple and touch the nozzle I get 170°. It doesn’t seem to matter what temp I set the extruder to, it will always be about 30° cooler than what the machine thinks it’s at. I currently have to have the extruder set at 260° to fool the machine to be able to print PLA.
Attempts to Fix:
This scenario sounds like a faulty thermistor, right? So I went and bought a few and tried each one; same problem.
Realized the 100k thermistors might not have the same beta value and didn’t want to try messing with firmware, so I bought an official Semitec NTC 100k 104GT-2 Thermistor and put that in. Same result. I disconnected it from the harness and measured its resistance at room temp and it’s at 100k, so this leads me to think it’s not the problem. I opened up the rambo box, disconnected the wires to the board and tested them for continuity to the connector for the thermistor, and they were good. I then tested the resistance of the wires and got zero, so they’re fine. Signals from the thermistor should be getting to the rambo board no problem.
Tried replacing the original 30w heater cartridge with a 40w one. Thought maybe it wasn’t getting hot enough and the 40w would be a nice upgrade. No change, except it heats up faster, which is nice.
I did PID tuning after changing out each thermistor and heater cartridge, but no luck. Tried rolling back to the first firmware version the printer came with and doing PID tuning again. Still no luck.
At this point I was running out of options and could only conclude it was the Rambo board, so I got a new one, put it in, flashed it with the latest firmware aaaaaaannnd it’s the same.
Thought maybe the heater block wasn’t transferring the heat from the cartridge throughout the block properly, so I made a new aluminum block and put a new nozzle in it and tightened everything as per the
online instructions from lulzbot, but no luck there either.
Maybe the filament is just dragging in the heat-break or is getting resistance from somewhere? I tried putting a new extruder stepper motor gear in the tool head, lubricating the bearings, realigning everything and reassembling. No better.
Finally, I bought a new block, new swiss 0.5mm nozzle, and put that together with the new 40w heater cartridge and the new 100k thermistor…and I get the same result.
I’m out of ideas. I’ve basically rebuilt the machine and there’s nothing left to change!!
I’m still getting the wrong temps at the nozzle and if it was off by 5° I would be happy, but 30° is way too much!
I’ve spent months trying to get this working properly and I’m starting to think the only solution is the dumpster. I’m losing my hair over this. Anyone have any ideas on how to fix this?
My only thought is the Fluke thermometer is incorrect, or perhaps you’re reading Celsius when you think you’re reading Fahrenheit? I know Fluke is a great brand name in electronic tools but… you’ve replaced everything.
I am reading celsius. That’s the units the printer uses.
I also thought that maybe the Fluke was mis-calibrated and was misreading the temps, but I happened to have a second one on hand, and that also obtained the same readings.
Even if I didn’t have the Fluke I could still tell the temps aren’t right. You know when you switch to a different roll of filament and you have to heat up the extruder so that you can manually force the new filament into it to get it started? When I do that at 205° for PLA, it struggles to ooze out the nozzle. I have to push the filament with a lot of effort to get it to extrude. Prior to this I used to be able to push PLA through the extruder with ease at 205°, with almost no resistance. It was practically a liquid when it came out. I miss those good old days…
When I look at the Marlin sources, they mention a 4.7 Kohm pull up resistor. I wonder where that is located. If it’s not on the Rambo board (which you say you swapped), then perhaps that could be the source of the discrepancy. The Marlin sources also mention some thermistors need a 1 Kohm pull up. I believe the LulzBot Marlin sources call out a “5” thermistor (see configuration.h, Thermal Settings, around line 250).
I think that resistor is in reference to the one that was on printers that had the Budaschnozzle, which I think the early Taz 5’s came with…maybe? I’m not sure. This is the part:
Pretty sure mine doesn’t have that since I have the hexagon hot end, but I could easily pull the wire loom off the harness and see if there’s a resistor soldered anywhere inline. I wouldn’t think there is though since I tested the resistance of the wires before and got zero on the meter.
I too found that the Marlin sources called for option #5 to be selected for the thermistor setting in the configuration firmware, but my understanding was that #5 is the default setting for the Taz 5 firmware, and that’s what I’ve using. Unless they sneakily changed that default to a different option number and swapped out all their downloadable firmware files online, I’m hesitant to think that’s the issue. But it does sort of seem that way.
I guess as a final resort I could try downloading the arduino software necessary to edit the firmware and see if editing those thermistor options has any effect. It’s just odd that if I’m using all stock parts and stock firmware that it wouldn’t work as is.
I have seen that thread before, and my situation does sound exactly like his, but the OP never came back to say if doing the PID tune fixed his problem or not.
I have done the PID autotune many times and it doesn’t have any significant effect on the issue. I could try entering the ‘C’ value to cycle the temperature more times than the default 3 times. Maybe that will get it more accurate, but I’m skeptical.
I wonder if I can cheat the system a bit by moving my thermistor so that it’s almost out of the heater block, then doing another PID tuning. That way, the thermistor would be far away from the heat source and the PID tuning would calibrate the heater cartridge to run hotter to get the desired temps. Know what I mean?
I do know what you mean. I’ve never done the PID tuning myself nor have I measured my nozzle temperature, I assumed everything was working correctly . I get how the problem came about and made you look closer. This is certainly a strange case. I did just replace a thermistor on one of my print heads, over tightened the set screw and that made the temperature readings swing wildly until it errorred with max_tmp error. Perhaps you over tightened the set screw just a bit? It’s working but not quite correctly? Try another thermistor? Tighten it just enough to prevent gravity from letting it fall out if you were to tilt it downward.
There’s no set screw on the thermistor; just a plate that’s held down with a screw.
I’ve already tried 3 thermistors and they all perform the same.
My latest attempt to kludge a fix was to pull the thermistor out of the heat block and put it back in so that it’s juuuuuust barely in the hole. You could yank it out with a gently tap with the tweezers right now. My thoughts being that if I get the thermistor further away from the heat source it should read cooler than normal because it’s barely in the block, thus the heater has to crank up the juice to get the block hotter, thus getting the results I want at the nozzle.
I’m kind of tricking it in a way. By doing this I’ve achieved a 15° difference rather than a 30° difference between the set temp and actual temp. I just don’t get why this is being so difficult. I’m 1mm away from having the thermistor completely out of the block. That’s just crazy to me.
I’m doing a test print now to see if it’ll work for now. My only other kludge would be to wrap something around the actual glass of the thermistor to insulate it so that it can’t pick up as much heat.
Bumping this, in the hope of updates on this issue!
I have a Taz6 DualV3 setup that has worked flawlessly for two years, and in the space of a few days began exhibiting the same symptoms as above. I rebuilt the hot ends and the thermistors and heating elements are new, etc. – still 30C or more too low, despite the machine reading that set temp is reached. Set at 255C the hot ends (both) are barely reaching 200C in-print.
Selecting temps at the machine VS in Cura does not change anything. PID autotune would only refine the PID settings, not like there are none to begin with. So, I haven’t tried that yet but OP did multiple times with no results so I stand by my statement that the process only fine-tunes the settings, which worked just fine for two years anyway?
Lulzbot support is NON-existent at this time! I have a hard time believing they will be around for much longer if they can’t at least have someone checking the forums, much less returning phone calls or emails!
I eventually got a response from Lulbot support, and they agreed it was strange and applauded the lengths I went through to try and remedy it, but ultimately had no other suggestions other than buying a whole new tool head. It would be nice to have an upgraded toolhead, but not exactly the solution I was hoping for.
My temporary fix of having the thermistor just barely in the block has been working for the most part if you want to try that.
Thank you for following up, Behrends. Very useful info, I am glad you had some contact with Lulzbot. I don’t think much of their original staff made the move to Fargo ND, so perhaps there is a lack of experience-based knowledge at the new headquarters.
A new toolhead will simply replicate the replacement of the same hot end parts we have already tried. What really got me was that your replacement of the RAMBO board (plus updating firmware) did not help, as that would seem like the last resort as far as throwing parts at it.
If only thermistors had a linear thermal/resistance curve - adding a resistor in series or parallel with the thermistors would be a simple enough trick. I might try it, nothing to lose! But it will correct for one temp and be wrong everywhere else, I think.
FWIW - the printer bed is dead on accurate, temp wise. Which really is even weirder if the PID loops all go through the same board and firmware…
I think Lulzbot had about 50 employees before the move, and now they have about 3. I could be wrong, but it sure seems like it.
Not only did I replace the RAMBO board and update the firmware, but I also tried installing all the variations of firmware that were ever released for the TAZ 5, and they all performed the same temperature-wise.
I think my bed is heating properly, but it doesn’t read that way on the fluke. It also reads a low temp, but I think that’s because I have an extra thick layer of PEI added to the bed which is dissipating some of the heat. I don’t have near as many problems getting prints to stick to the bed as I do extruding, so I’m not too concerned about it.
Maybe it is just a bad thermistor…that I got 3 times in a row. Maybe the 4th time is a charm?
I am using Octoprint and was not aware it can have temperature offsets. However, I don’t think that’s the issue in this case because most of my temp testing was performed at the printer by using the actual controller. I had to be nearby to measure it’s temperature with the Fluke meter.
I would replace the wiring between the board and the heater cartridge. You might have a wire with some broken strands that isn’t able to deliver the current necessary for the PID settings to function properly.
It is a long shot but I had a bed heater stop working even though I could measure voltage and continuity all the way from the board to the connector at the heat bed. The heat bed worked on another printer. Finally, I took the harness off and one of the bed heater wires was hanging on by a couple of strands.
I do believe I checked the wires, both visually and with a multimeter. No breaks or damage I could see, and when I had the machine warmed up I was back-probing the connector for the thermistor at the RAMBo board, and it was spitting out the correct resistance values for the temperatures.
I could check that over again though.
. I get how the problem came about and made you look closer. This is certainly a strange case. I did just replace a thermistor on one of my print heads, over tightened the set screw and that made the temperature readings swing wildly until it errorred with max_tmp error. Perhaps you over tightened the set screw just a bit? It’s working but not quite correctly? Try another thermistor? Tighten it just enough to prevent gravity from letting it fall out if you were to tilt it downward.