3D Printing (Part 10)

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Almost shocking ! As I was not very satisfied with the quality of my prints, and after experiencing a strange awful printing incident (Wires every where, big melted material blob on top), I started having some sort of concern about temperature readings.

I used a very thin thermocouple connected to a pro grade thermometer (Testo 945). Then I managed to  lock the tip of the thermocouple firmly on the heated block and started performing measurements. And the readings where alarming. Although the set point for ABS was set to 245°C, the reading showed a good 280°C ! Some posts from the Vertex forum rang my bell, but none reported real data. Now it’s done. The original sensor is very badly reporting the print head temperature.

I quickly found on the Internet some vendors of thermistors (100k Ohm), some of them offering for a very cheap price assembled thermistor. So, why bother ? Here is the one I chose.

sensor_4

For less than 3€, the thermistor comes insulated and nicely wired

sensor_5

The I used a Faston connector adapter

sensor_1

that I modified in order to fit the print head profile and sensor size

Note: Watch out, the bead is fragile do not over tighten it

sensor_2

Once you are happy with the mechanical arrangement, remove the sensor, add some thermal compound around the bead and put it back. Remove the original thermistor wires from the print head PCB and place the new ones after adjusting their length.

  sensor_3

sensor_6

And now the readings are alright, no more than 5°C in difference between the thermocouple and the thermistor. The benefit from this modification is that you can retrofit it in case you find a better option.

Short discussion about the original sensor: Firstly, it is pretty risky to install it as specified, “feeling the bump” from the insulated tube. A minimal improvement would consist in removing the sleeve, marking the wire length in order to make sure that the glass bulb is properly fitted in its hole. In my opinion, what makes this big difference in readings is that the hole is too wide and the insulating tube is … insulating too much. I am afraid that using thermal compound would not help bridging the thermal gap. Am I the only one with this problem ? Didn’t it occurred during testing at VELLEMAN labs ? That’s strange ! And dangerous for the “plastic” parts all around.

And by the way, using 230°C for extruding ABS is just fine.

HTH

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