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Archive for May 10th, 2013

Makergear M2: Nozzle Temperature Sensing

The stock Makergear M2 hot end uses a 100 kΩ thermistor for temperature sensing. A wrap of Kapton tape holds it against the brass nozzle, with a stretchy fiberglass-lined tube for protective insulation and a bit of pressure. This picture shows the tape pocket around the thermistor, with my thumbnail on the left:

M2 Nozzle Thermistor - as-shipped

M2 Nozzle Thermistor – as-shipped

Peeling back the tape a bit shows the thermistor against the nozzle, with the glass bead reflecting the LED ringlight around the macro lens adapter:

M2 Nozzle thermistor - exposed

M2 Nozzle thermistor – exposed

The RAMBo board in the M2 has four thermistor inputs and no thermocouple inputs, which surely drove the decision to use themistors. I want to use thermocouples with the LinuxCNC controller, because they’re more compact and happier at higher temperatures.

So I unwrapped the nozzle and lined up a thermocouple beside the thermistor:

M2 - extruder - thermistor-thermocouple

M2 – extruder – thermistor-thermocouple

Where a dab of JB Weld firmly bonds them to the nozzle:

M2 - extruder - epoxied sensors

M2 – extruder – epoxied sensors

As nearly as I can tell, the JB Weld that I used on the Thing-O-Matic is still going strong. I think the trick is to not apply mechanical force to the bond when it’s hot; secure the leads firmly and use the epoxy only as a thermal connection. Yes, you can get fancy higher-temperature adhesives, but this seems to work well enough.

For the moment, I’m using ordinary cotton cloth secured with Kapton tape as insulation:

M2 - extruder - cotton insulation

M2 – extruder – cotton insulation

The brown dot that looks like a bead is actually a flat stain on the nozzle.

The insulation should become something more suited for high temperatures, perhaps the ceramic fiber I used on the Thing-O-Matic, but cotton will suffice for now.

Now, wisely is it written that a man with one thermometer knows the temperature, while a man with two thermometers is never certain…

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