Prusa MK3S Hotend DIY Mod
creation date: 2025-03-11 13:09
modification date: 2025-03-11 13:09
The Problem
Over the last 8 years that I have owned this wonderful Prusa MK3s 3d printer, I have spent countless hours maintaining the dang thing. The most common maintenance procedure I find myself doing is swapping out the hot end, heater block, thermistor, and the heat transfer threaded adapter, i forget what its called.
I've probably changed it out 20 times at this point. Recently I found out why I had to keep changing it: I've been incorrectly assembling the hot end assembly this whole time!
Oozing
What kept happening was, everything would be fine for the first couple prints and then I would start to see oozing from the nozzle. I'd tighten the hot end (at 230C) and everything would be great for a while. Then the oozing would start again. Tight then nozzle again. Repeat until eventually the oozing would start coming out of the top of the heating block. In some cases it got so bad during an unattended print that it totally caked the cooling block and the heating block together.
Fuzzy Skin
I recently learned how to use fuzzy skin for my prints in prusa slicer and have been experimenting with the textures. Little did I know, some settings for fuzzy skin will THROW your extruder assembly around. I believe this had something to do with why the hot end was loosening every couple prints.
Thermal Paste
Luckily I work at a place filled with nerds that also love 3d printing. I told them what was going on and they suggested I use thermal paste around the threaded insert only in the part that goes into the cooling block. That worked!
I started printing again with confidence until it happened again. Oozing out of the top of the heating block. What the heck is going on?
It was at this point that I realize that when I was tightening the hot end, it wasn't actually getting any tighter because the heat transfer threaded insert wasn't fully seated into the cooling block.
How could that be? I made sure I tightened it in a vice when I assembled it. Well it turns out, over time as the printer moves, this thread was slowly loosening. In the middle of the night trying to salvage a bad print, it hit me.
Just keep the cooling block from rotating! That has been the crux to this machine this whole time!
The Solution
I tapped the side of the cooling block? and threaded an M3 screw into it. This will give the 3d printed part of the hot end assembly something to grab onto. Additionally I drilled a small hole in the assembly for the screw head to click into.
This actually did the trick and I have not seen any oozing since installing this mod.
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Increased Print speeds
Since doing this mod, I figured i'd push the little prusa a bit and increase the print speed to 200%. To my amazement, they prints are coming out flawlessly. So so sick.