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We have a Makerbot Replicator 2X at our school. I have a class in the computer lab and one of our focuses is using the printer. Currently, it is not printing properly. We are using PLA at 210 degrees Celcius. The built plate is not heated (using Build Tak). This has worked very well in the past. The problem is that when the extruder goes to lay down plastic, the filament is too hot and curls up in a clump around the extruder. This is characteristic of when we first tried PLA at a higher temperature. I think that our heat sensor is not working properly. Does anyone know how we can fix this problem? Is there a way to calibrate the sensor is should we install a new one?

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  • $\begingroup$ I noticed that your question has a few answers available and has been open for a while, just curious if any of the available answers was able to help. If not, then what questions do you still have? $\endgroup$ – tbm0115 Jul 3 '16 at 20:19
  • $\begingroup$ @tmb0115 I selected the proper answer. We replaced the thermocouple and it started working again. $\endgroup$ – Ryan Mar Jul 5 '16 at 16:19
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Overall, it is unlikely that the problem is temp sensing accuracy. There are only a few things that will throw off the thermocouple's reading:

  • Poor thermal coupling between the tip and the hot block, such as if the tip has partially pulled free of the brass thermowell crimp (this will make the hot block hotter than the reported temp)
  • Loss of electrical insulation between the tip and the hot block, plus some ground loop noise or stray voltage on the hot block (this will typically add noise to the reported temp)

You should be able to visually check for the first, and test for the second with a multimeter. The resistance between the board end of the thermocouple leads and the brass thermowell at the tip should be infinite / out of range.

To actually check the thermocouple calibration, you have a few options:

  • Easy: Look at the behavior of the printed plastic. PLA that is too hot will smell of pancakes/waffles much stronger than normal, or even smell burnt. The printed material may be more shiny than usual. It will string and ooze more as you print.
  • Moderate: Secure another reference thermocouple (such as might come with a digital multimeter) tightly to the hot block with some Kapton tape, somewhere the aluminum block is exposed. The external TC should read within a few degrees of the printer's TC. (Assuming you get it attached well enough.)
  • Hard: Place the tip of the TC in boiling water to check if it reads 100C (or slightly lower if you live at a high altitude). Repeat with well-mixed ice water to check if it reads 0C. Both measurements should be within a couple degrees. You will probably need to dismantle much of the extruder to detach the thermocouple for this test.

But, again, the problem probably isn't the TC. It's more likely either a bed tramming issue (eg too much gap between nozzle and surface) or the BuildTak is degraded and not adhering. This can happen if you do a large number of prints in the exact same place, or get the surface oily, such as with fingerprints. Try a fresh sheet of buildtak or cleaning it with rubbing alcohol and moving the print to a different location.

In some rare cases, low-quality filament or filament stored in very high humidity may not stick well. This is pretty rare though. For the most part, if your nozzle gap is right, any extruded plastic will stick to Buildtak.

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The temperature is fine.

In my experience the filament curls up only when the extruder is extruding way up, far from the plate: are you experiencing this while actually printing?

If yes: recalibrate the printer so that the extruder is closer to the build plate and this shouldn't happen. For the filament to curl up it means you are way higher than you should be.

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    $\begingroup$ "Recalibrate" meaning adjust the leveling screws using the built-in leveling script from the LCD, or by printing a level check STL. $\endgroup$ – Ryan Carlyle Mar 1 '16 at 15:43
  • $\begingroup$ Also, if the problem is really about the distance between plate and extruder, and not the temperature, I would suggest editing the question title accordingly. $\endgroup$ – gcatalfamo Mar 1 '16 at 16:14
  • $\begingroup$ Could also be finger grease on the Buildtak. $\endgroup$ – Ryan Carlyle Mar 1 '16 at 17:19
  • $\begingroup$ It wasn't the distance between the plate and extruder. Will be trying more options soon. @gcatalfamo $\endgroup$ – Ryan Mar Mar 7 '16 at 14:27
  • $\begingroup$ Could you post a very close-up picture of the filament curling up while printing? It might help us understand your problem better :) $\endgroup$ – gcatalfamo Mar 7 '16 at 15:07

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