Hot End Issues - Possible Heat Break Alignement Issues  

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cyn42
(@cyn42)
New Member

Apologies for the book, but I want to make sure I cover the right context for my question!

I have been having increasingly frequent issues with my MK3S, and decided to replace the hot end. I bought a replacement MK3 Hot end (assembled), and an MK3S PTFE tube, but I was nervous about replacing it myself, so I took it to a 3D printer repair place to have it done. It came back with the new hot end and a silicon sock

Since I've had it back, it will print 1 or 2 things, and then it will jam, or not extrude (well or at all). A couple cold pulls will fix the problem, but it keeps happening, and there is a hard ring in the filament after the pull. I checked the nozzle, and it looked too low (like, 1.5mm instead of .5 mm below the heat block). Tried to tighten it, but wouldn't tighten anymore. And then I noticed that the MK3S tube I'd bought was still sitting in the box, uninstalled.

So tonight I'm going to dissassemble it to at least install the proper PTFE tube, but I am wondering if it is possible that the heat break is screwed too far into the heat block, preventing the nozzle from being screwed in as far as it should be? If so, is there a way I can safely unscrew it without breaking / bending it? I've been looking at replacement tutorials, but I'm not sure how I would grip the hear break to apply enough force if it was stuck and not damage the threads. (I've ordered a new one in case)

 

Posted : 09/04/2021 8:24 pm
bobstro
(@bobstro)
Illustrious Member
Posted by: @cyn42

[...] I checked the nozzle, and it looked too low (like, 1.5mm instead of .5 mm below the heat block). Tried to tighten it, but wouldn't tighten anymore. And then I noticed that the MK3S tube I'd bought was still sitting in the box, uninstalled.

If the heatbreak is screwed so far into the heater block that the narrow neck (the "break") is partway into the block, that will affect the ability to cool, which will result in eventual heatcreep that might explain exactly what you're seeing. The best way (IME) to assemble the hotend is as follows:

With everything disassembled:

  1. Hand screw the nozzle into bottom of the heater block so there's just a bit more than the < 1mm gap you want visible.
  2. Hand screw the heatbreak into the top of the heater block so it butts up against the nozzle. Don't overtighten. We do that at heat later.
  3. Apply some thermal paste and hand screw the heatbreak into the heatsink. Clean up any messy thermal paste (q-tip & alcohol work well).
  4. Check alignment of everything.
  5. Insert heater cartridge & thermistors.
  6. Reassemble and route cables.
  7. Check alignment again.
  8. Heat to 285C.
  9. Do final tightening of nozzle against the block and verify the < 1mm gap.

It's fairly foolproof this way and there should be little chance of screwing up the insertion distances.

As far as disassembling, be prepared to replace things, but if it hasn't been used heavily, most parts should unscrew without too much force. Just go slow and pay attention to where you're applying stress at each step. Nothing needs a lot of force.

My notes and disclaimers on 3D printing and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan...
Posted : 10/04/2021 5:57 am
cyn42
(@cyn42)
New Member

@bobstro

Thanks so much for your response; I was able to take the hot end apart and reassemble it, and everything is working great now. 

Posted : 13/04/2021 2:02 pm
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