hot-end-thermal-management [Bukobot 3D Printer Instructions & Docs]

=====Hot-end Thermal Management=====


Ideas for how best to do thermal management on the hot-end should go here.

Insulation, air flow from the fan, debugging heating problems...

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Consider the hot end:

{{wiki:jitsbuild:hot-end.png}}

The brown insulator in the middle is the thermal boundary.  The part below it is to be kept hot.  The part above it is to be kept cool.

Don't allow the air flow from the fan to hit the part below.  Any part of it.

The part above, on the other hand, must be kept cool, so hit that with the airflow.

You need to construct somehow a thing that will keep the airflow where it is needed, and away from where it is not.

Furthermore, convection currents will arise next to the hot part, and carry heat away.  Anything you can do to stop this flow, or slow it down, will help.

Hot air rises, so a box open on the bottom but closed on the top can contain it.  Construct such a box, out of materials that can withstand the high temperatures.  Polyimide tape is provided, but you could use additional materials.

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Proper heating cannot occur unless everything on the hot end is wired up properly.  That's four wires, two from the heater resistor and two from the thermistor.  None of these wires is polarized.

If you power down everything, you can use an ohmmeter to check the wiring.  The spot nearest to the hot end where you can touch a wire is right next to where it enters the terminal block on the X carriage.  Measure the resistance between that point and the place where the wire connects with the controller;  it should be near zero.  To probe the thermistor from the controller end, pull the thermistor connector off the controller just enough to reach under it and touch the pin with the probe.

Alternatively, you can measure the resistance across each resistor from the controller.  From there, the heater resistor should be about 7.5 ohms and the thermistor should be roughly 90,000 ohms (this one varies a lot, depending on the temperature of the room).

If you get wrong numbers, check the wiring.  Make sure you haven't hooked wires up to the wrong places.  Make sure you haven't clamped down on the wire's insulation instead of the wire itself inside the terminal block.


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