I'm experiencing some extremely repeatable underextrusion that increases with extruder feed rates above 500mm/min with no skipping of the extruder motor and no slipping of the filament. I've gone through a round of support emails with E3d but we didn't get to the bottom of it. The faster I go, the more it underextrudes.
I have an E3D PT100 sensor on a Duet Ethernet with PT100 board as my hotend thermistor, a normal EPCOS100k thermistor for my bed and my chamber heater monitor. I've got an E3D Titan extruder with a common stepper motor, not the smaller pancake motor. I've got a Volcano block with the 0.8mm and 1.2mm nozzles. At room temperature, all thermistors are within 0.3C of each other, and I've confirmed that temp compared to room temperature with a Fluke thermocouple. Then I kapton taped my chamber thermistor to the volcano block, and graphed the difference in temps up to 285c. Turns out the taped on chamber thermistor reads consistently 20C low once it gets above about 100C, but I'm not sure if that's normal for that thermistor, the less contact with the block than the cartridge PT100, or some other factor. Anyway, I did some more testing with extrusion rates and temperatures.
I tested marking out and then extruding 1000mm at various feed rates. I started at 440mm per minute, which was giving excellent print results, but is a pretty slow print on a big layer height. I was able to easily confirm my steps per mm were correct this way as well.
I found that at 245C on the coolest reading thermistor, 440mm per minute got perfect results. No measurable slippage.
Leaving it at 245C, I tried 500mm/min, 600mm/min, 700mm/min, and 800mm/min several times each, cleaning the hobbed bolt with a brush between each test. I used new ABS of a brand I've had excellent success with.
- At 500mm/min I was getting 5 to 10mm of underextrusion (10mm before my mark still sticking out of the point I measured from).
- At 600mm/min I was getting 15 to 25mm underextrusion,
- at 700mm/min I was getting 25 to 40mm underextrusion, and
- at 800mm/sec I was getting 100mm underextrusion.
The temperature graph was steady, there was no drop or increase in temp more than about 2C during these tests.
I then returned to 600mm/min (a little underextrusion, same as before) and repeated the testing, increasing the hot end temp 10C per try. I went from 245C up to 285C in 10C increments, and over that 40C range, the underextrusion improved by only about 5mm, still underextrusion by about 20mm.
I dropped the temp back to 265 (it was starting to stink at 285), and then began retesting at 600mm/min, increasing tension by 1 turn on the knob each try. I got to the maximum tension where I was no longer able to release the filament by pushing the lever over, with no more than 5mm underextrusion improvement. (still underextruding by 15 to 20mm).
I tried pushing 1000mm at 800mm/sec on my long-suffering hard-used delta that has a direct drive bowden extruder with a large motor on it, and I was able to extrude at 15mm/sec (900mm/min) on a standard 0.4mm nozzle V6 hotend. On that one I was able to extrude fast enough to see a temperature drop without any grinding but I didn't remember to note the feed rate for comparison after 900mm/min. The 96oz/inch motor will actually stall and start skipping before the filament grinds. I've got a standard 40oz/in stepper on the titan, with no skipping or stalling ever occurring that I can tell. I've even pulled on the filament so that I could experience what stalling or slipping would be like, and it's a very audible clicking noise with pulsations through the machine. None of that occurs during the normal higher speed underextrusion.
I've tried turning the microsteps down by half at a time all the way down to 1/2 (adjusting the steps per mm to be correct), and turning interpolation off and on at each setting, with no change in the results.
Does anyone have any ideas what could be wrong? I know a volcano setup is capable of more than this. I've found people being able to get 40mm/sec (2400mm/min) out of theirs.
Any ideas? I've been working on this for weeks and I'm all out of things to check. There's nothing mechanically or electrically wrong that I can find, I've even rewired the motor twice and used two different (though identical model) motors!