This short article is about how I got a headache from a damaged PTFE tube in the Kingroon KP3S 3.0 hot end and how I upgraded it to an all metal hot end afterwards.

For my WeirdCube 3D Printer project I started to print ASA and PETG with it. Against better knowledge and advice to push the temperatures beyond 220°C I printed ASA at 240°C and later on PETG at 225°C.

Maybe you remember the Kingroon KP3S 3.0 from my older posts:

It's a very fine little and cheap printer. I only had good results with it. With the WeirdCube 3D Printer project (see my other posts) there came a need to print more durable materials, like PETG and ABS/ASA.

Don't Trust 3D Printer Max Temperatures

One 3D Printing Discord Server told me to not use a stock cheap 3D printer to print PETG and ABS/ASA at temperatures around 230-240°C, because the PTFE tube in the heat break will deteriorate and emit nasty fumes. And there were some articles on the internet that warn about this too. The other 3D Printing Discord Server I was on assured me, that nothing bad will happen. That they also print PETG fine at up to 230-240°C. Requiring better plastic parts for the WeirdCube I tried my luck with ASA at 240°C.

After building a super quick and dirty enclosure for my printer from cardboard and plastic foil I managed to print ASA (with the help of some Acetone + ASA adhesive on the built plate) at 240°C with 80°C bed temperature on the Kingroon KP3S.

All was fine, but after a day printing a few little test pieces (A MakerGrid 1x1 Build Cube) the room I was printing in filled with fumes. And once I entered that room, I quickly got a stinging headache. I realized quickly that it might be due to the ABS/ASA I was printing, not yet realizing it might be that I print too hot for the Kingroon KP3S.

It took a few days of venting the room until the headache inducing smell was out.

I switched to printing PETG instead. It's durable enough for prototyping the parts for the WeirdCube. So I went with it. I printed PrimaCreator's PrimaSelect PETG at 225°C on a 65°C hot build plate. First everything was fine, I happily printed away and no nasty fumes were around. Well, at least until I got the stinging headache again!

I read online that there are no harmful or at least headache inducing fumes generated from printing PETG. So I realized, ok, it must be the PTFE tube.

Taking apart the Kingroon KP3S hot end quickly revealed the culprit:

It was a shrunken and burnt PTFE tube. Smelling at the burnt PTFE tube quickly confirmed that it is the source of the nasty headache inducing fumes in my room.

Upgrading The Kingroon KP3S 3.0 Hot End

My printer was broken. So I had to fix it. Lucky as I was I already had some new V6 J-Head hot ends around. One was the Mellow All Metal V6 J-Head Hot End with a bi-metal heat break:

I bought it on Aliexpress a few weeks ago. Taking apart the KP3S extruder and hotend was more or less easy. Watch out for the spring in the Titan extruder clone. It slipped out two times already and jumped through the room. Luckily I was able to find it again. Watch out for this!

I took the heater from the old KP3S hot end and replaced the thermistor with the one that came with the Mellow hot end. Don't forget to fixate the new nozzle with a heated up hot end. You don't see the heat in the following picture:

Reassembling the extruder was not hard:

One unanticipated problem was that the tool head shroud would not be suited for the length of the new nozzle. The fan shroud touched the build plate before the nozzle would.

Designing A New Fan Duct For The Kingroon KP3S

This unfortunately meant, I would have to print a new fan duct. Printing PETG does not require part cooling luckily, so I could print fine with the fan dangling on the side of the printer.

It would be a fun project to design my own fan holder for this printer I thought and after a day or two of designing and prototyping I arrived at this design:

I tested out the fan duct I designed with the water test. I have to be honest here, and I don't exactly understand what the test tells me. But as far as my judgment goes, the air hits the water a little bit too early and not exactly under the nozzle.

But for this iteration and for the moment I decided it would be fine enough for my needs. Luckily I thought ahead in my design and I made the fan duct easily swappable using the MakerGrid clips!

If I decide to iterate on the fan duct design in future I will be able to quickly do that.

Kingroon KP3S MakerGrid Fan Mount Overview

Here I give an overview of the assembly of the fan duct and the parts you might need to assemble it. The whole design consists of three 3D printed parts (not including the MakerGrid clip)

You can find the files for that here:

• 1x kp3s_3_0_hotend-fan_duct.stl
• 1x kp3s_3_0_hotend-fan_mount.stl
• 1x kp3s_3_0_hotend-hotend_mount_plate.stl
• 2x MakerGrid clip-clip.stl

You will also need 2x M4x10mm screws and 2x M4x20mm screws:

And last but not least here is the whole thing mounted on my Kingroon KP3S, it fits nicely with the new Mellow V6 J-Head hot end height: