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Hot-Ends review

A long melt-zone can show up as both a lot of spring (compression) in the melted filament and also increased ooze from the nozzle end. In my use of different nozzles it seems better to have a shorter melt-zone and so less spring /compression in the filament and minimal side-wall grip so when pressure is released oozing is minimized. You can’t just have a bigger barrel size as this usually produces a plug at the thermal transition zone actually causing oozing and other problems when trying to retract the filament during printing.

Materials Wherever possible I have tried to use similar materials and batches for testing, I use PLA mostly, then Nylon, PET and lastly ABS. Not all materials are the same, so as they say ‘your mileage may vary’ Wood/chalk/mineral filled filaments, conductive and soft materials all bring their own challenges and will be covered in a future article.

Feature

element. Both of these have issues too, but they were usually less powerful than most of the cartridge heaters being fitted now. I have always limited the power available to the hot-end in firmware. While this does not take away the risk of a shorted Mosfet applying full power, it will at least limit the energy going into the hot-end when in normal operation. It may take slightly longer to get to temperature, but this can also have benefits for the temperature control algorithm (PID loop) that is aiming to reach a target temperature without too much over-shoot. If you do adjust the maximum power to your hot-end do make sure you re-run the M303 Auto-tune again and enter the new values. You can get 24V 40W heaters, running these at 12V is another option to lower the power. Ideally we need a ~12W 12V Cartridge heater for most general 3D printing requirements.

Nozzle Heating - a word of caution. Many nozzles not come with a cartridge heater, these heating elements are usually well over powered for use in a 3D printing hot-end. The standard types mostly available are usually rated 12V at 40W. This is a lot of power and can get your nozzle temperature well in excess of 400 Degrees C. Be aware that if uncontrolled full power (usually +12V) is applied to a hot-end it’s going to get really, really hot indeed. A 12V 40W cartridge heater running at full power for just 15 minutes in free-air will glow orange then white hot, expand the metal case and start to break-down the fibreglass insulation. It’ll melt almost anything it touches and make things catch on fire. Back in the early days of RepRap is was common to fit nichrome wire or use a vitreous enamel resistor as a heating

Cartridge heater

Running a cartridge heater at 12v, this is current limited 2.7A by my power supply, still glowing red-hot and burning the insulation. REPRAPMAGAZINE

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RepRap Magazine Issue 3  

The third issue of RepRap Magazine. Interview with Nicholas Seward, Paste Extrusion, Hot-Ends, and much more.

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