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I want to use my Ender 3 as a multi-filament-printing printer

As many users already have asked, printing PLA with an all-metal hot end is not really recommended.

But, if I am attempting to use my stock Ender 3 printer (no hardware and software modifications) as a safe indoor 3D printer that can both print PLA and PETG, without risking any fumes coming out of the PTFE tubes.

How may I reliably print PLA with an all-metal heat break, without any further hardware modifications?

Are there any reliable slicer settings (such as print speed, retraction, etc.) that should be systematically tried?

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    $\begingroup$ All printers are at least a bit smelly/fumey. If you want to avoid that, an enclosure that is vented through a filter, or vented outside is a solution. $\endgroup$
    – Criggie
    Dec 14, 2023 at 2:14
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    $\begingroup$ Can you expand a bit on what you mean by "printing PLA with an all-metal hot end is not really recommended."? Prusa printers are known to be reliable, and have all metal hotends. I've been printing PLA on my Prusa MINI+ for years very reliably (and more recently a Prusa XL, again with all-metal hotend). $\endgroup$
    – RobM
    Dec 27, 2023 at 13:42

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You can look up the material properties of Polytetrafluoroethylene (PTFE) and see that its glass transition temperature (when it softens) is around 115 °C, and it melts at 327 °C. The PTFE in a not-all-metal hotend will be in the heatbreak which is significantly colder than the hotend, and should not reach 115 °C.

The plastic casing which holds the heatbreak is typically injection molded ABS which softens at 105 °C. So your hotend would begin to shift in a softened carriage before the PTFE began to soften.

The fumes you are worried about are caused by off gassing, which may be a better term to search for if you want something with hard numbers you can reason with.

That said, if you can reason about the maximum temperature your PTFE will experience in the heatbreak (which should be significantly colder than the temperature of the nozzle), you can use this safety chart to reason about how dangerous (or not) it is to be near (see Capricorn's Safety Precautions).

Chart of PTFE temperatures against 'Is it safe?'

As regards the safety of an indoor printer, PLA does not emit a lot of Volatile Organic Compounds (VOCs) and is generally deemed "safe". (ABS is known to emit a lot, and is known to cause headaches). PETG seems to emit more than PLA, but still low at 550 parts per billion (ppb).

That said, all plastics emit some amount of VOCs when heated, so it is always best to print in a well-ventilated area. Personally, I print in my bedroom and spare room and just leave the doors to the rest of the house open, and those little vent slots you get at the top of windows have been enough to keep the air in the house fresh.

(If I print ASA or ABS I absolutely close the doors during printing, then air the room with an open window for 10-20 min when it is done: you don't want the ambient temperature too low when printing - causes excessive warping and other issues).

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