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

===== Hot-end Thermal Management  -  Discussion Page =====


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

Insulation, air flow from the fan, how to debug 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.

(Note that the fan mount can be mounted in two different positions, and this will change the air flow.)

You need to construct somehow a thing that will keep the airflow where it is needed, and away from where it is not.  (Polyimide tape applied to the bottom surface of the multi-lobed aluminum part right above the thermal boundary would be a good place to start, although that alone is probably not enough.)

In addition to the air flow from the fan, convection currents will naturally arise next to the hot part, and carry heat away.  Anything you can do to stop this flow, or slow it down, will probably 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.  Obviously, you must provide a way for those four wires to escape from the box, without letting too much air leak through.

Just putting some tape around the heater block (the rectangular part near the bottom) may not fully solve the problem, as the metal cylindrical part will also leak heat.

There is some concern that completely enclosing all of the metal parts below the thermal boundary may cause the brown insulator at the boundary to overheat.

The best way to insulate the hot end is a matter of active discussion.  Solutions that are demonstrated to work well should be shown here.

Remember that a solution that works today may not work on a much colder day.  Experimentation required.


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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 ohms and the thermistor should be roughly 90,000 ohms (this one varies a lot, depending on the temperature of the room) [is that number right?].

If you get significantly wrong numbers, like infinity or zero, 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.

If you have dual extruders, make sure you haven't gotten one extruder's thermistor connected to the other extruder's thermistor connector on the controller.  Likewise, make sure you haven't got the heaters swapped.  Decide which extruder is going to be #1, and which is #2, and be consistent all the way through.

To make sure your thermistors are working properly, you can do a sanity check with a high-temperature thermometer  (infrared, or a meat thermometer?).  Get your user interface running on your computer, power up your hot ends and see what the computer thinks the temperature is.  Then measure the temperature of the heater block with another thermometer and see if it agrees.  Remember to properly convert between degrees C and F if necessary.

Make sure the 115V/230V switch on the side of your power supply is set correctly for your location.

Check that the spade lugs are solidly crimped onto the cable that connects the power supply to the controller.  Check the power supply voltage at the power supply screw terminals (-V to +V) and at the controller screw terminals;  they should be nearly the same even when the extruder is being heated.


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