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Nozzle cleaning… what’s really going on  

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Tobycwood
(@tobycwood)
Estimable Member
Nozzle cleaning… what’s really going on

This is pure inference since Prusa seems to think it’s users don’t need to know or fully understand what this machine is doing or why… they’re incorrect on that…

Why the nozzle cleaning? Plainly it’s to ensure accuracy to the load sensor which reads pressure at the tip of the nozzle which acts as the z limit switch as well as the z probe for z height offsets (what Prusa incorrectly calls the mesh). As such, it looks like an assumption was made that there will typically be material at that tip which could in turn make the load sensor reading inaccurate. So someone decided that this tip must be automatically cleaned off by the machine. Essentially the “wipe” which Prusa has ignored. So their approach is to touch the tip of the nozzle on to a well heated build plate (hence the probable need to have the heat absorption wait) and have the material stick to the plate a number of times and each time the load sensor should sense that the tip gets closer until it stops changing. Now, if the material on the nozzle tip does not stick to the plate and instead stays on the nozzle then it simply does it again and again until it gives up and moves the extruder to the front… what Prusa neglects to tell its user is that they should then manually clean the thing off (I use a paper towel) after which the user selects from the ui panel to try again and hopefully this time sense a clean nozzle tip before doing the z probing.

So if these inferences are incorrect someone please correct me.

Posted : 16/11/2023 8:57 pm
Acht
 Acht
(@acht)
Trusted Member
RE: Nozzle cleaning… what’s really going on

I actually thought that all that was already known and kind of expect everyone who has a machine like an XL would come to that conclusion. But good to clarify it anyway.

Posted : 16/11/2023 10:13 pm
Zappes liked
Jeggo
(@jeggo)
Estimable Member
RE: Nozzle cleaning… what’s really going on

I case you did not know this video deals with this problem:

https://www.printables.com/de/model/462473-prusa-xl-series-nozzle-scrubber-brush-update-now-w

Posted : 17/11/2023 8:45 am
gareth.ky
(@gareth-ky)
Active Member
RE:

I suspect we can change the stock nozzle cleaning routine to wipe over a wiper.

  • It looks like there is plenty of room to mount a nozzle wiper. Either in front of the tools or front corners of the bed (or both).
  • The cleaning should be triggered by the start gcode in the slicer, so we can modify it.

PTFE tube works well on that other brand of printers. Printables has some mods we might try adapting: https://www.printables.com/model/452240-bambu-x1p1p-nozzle-wiper-brushptfe

The Voron community has had a go at adapting this already:

I'd also like to change the start routine to not hold the tool over the bed while the bed "absorbs heat". It just sits here an oozes filament. I'd rather leave the tool parked and wait for it to heat up after "absorbing heat" to limit oozing. Tools should be parked unless  they are in-use.

Posted : 21/11/2023 7:56 pm
Razor and Area51 liked
Tobycwood
(@tobycwood)
Estimable Member
Topic starter answered:
RE: Nozzle cleaning… what’s really going on

If you use that wiper mod be sure not to use brass or steel brushes. They can and will damage the relatively expensive nozzles. Use coarse horse hair versions and it’ll be ok…

Wiping is tricky thanks to the load cell sensor… otherwise I go to the solution I used on my E3d… silicon pad which fully cleans the entire nozzle, but it would easily set off the crash sensing.

However, I’m not seeing any string issues at all because as I’ve posted elsewhere I lower the temps on my material and I always “Retract on tool disable” to 11.7mm to get the material out if the melt zone when parked.

Posted : 01/12/2023 1:06 am
Jeggo
(@jeggo)
Estimable Member
RE: Nozzle cleaning… what’s really going on

Why does Prusa recommend to clean the nozzle with a brass brush?

Posted : 07/12/2023 9:15 am
Jeggo
(@jeggo)
Estimable Member
RE: Nozzle cleaning… what’s really going on

@gareth.ky: I just added the tool parking to the printer setting.

Look for the line G29 G ; absorb heat

P0 S1 L1 D0; park the tool to prevent oozing <-- added command
G29 G ; absorb heat <-- original command
; select previous tool again
T{initial_tool} S1 L0 D0; <-- added command

Just running the first print on my 5 head XL. The print only uses one tool. But I think the added commands should work for all tools.
Use at own risk 😉 

Posted : 07/12/2023 10:29 am
Tobycwood
(@tobycwood)
Estimable Member
Topic starter answered:
RE: Nozzle cleaning… what’s really going on

Yah… I do recall seeing that somewhere and I was a bit stunned by it. Brass nozzles are soft. Even softer than brass brushes. The former are machined while the later are hardened for polishing work. Using a harder material than your nozzle will damage the nozzle. It’ll be ok the first time, then the second but soon you will see distortion in the extrusions. Don’t believe me? Ok… try it for yourself! I simply wipe it with a paper towel.

From my perspective Prusa sometimes seems totally clueless about a lot of things. But i can imagine if all you know is from Prusa you may think they are the know all be all for hobby 3d printing. They’re not!

Posted : 07/12/2023 4:23 pm
Tobycwood
(@tobycwood)
Estimable Member
Topic starter answered:
RE: Nozzle cleaning… what’s really going on

The “nozzle sealers” can only do so much. If you park a tool with material in the melt zone it will ooze down on to the nozzle sealer. When you heat up again and move the tool out of the parking place it will leave a string.

or… if at the end of the print you park and leave material in the melt zone, again it will ooze down and then it will be on the tip of the nozzle when the print starts making the fw nozzle cleaning routine to try to get it off, but it will likely not and the routine will fail.

Posted : 07/12/2023 4:28 pm
Jeggo
(@jeggo)
Estimable Member
RE: Nozzle cleaning… what’s really going on

At least the nozzle cleaning does not fail so often. If the tool is parked during heat absorbing the nozzle stays clean. Otherwise the oozed string at the nozzle is pushed on the print bead and most times the nozzle cleaning fails. Before I made the parking mod, I removed the oozed string from the nozzle just before the heat absorbing ends.

Posted : 07/12/2023 5:11 pm
Tobycwood
(@tobycwood)
Estimable Member
Topic starter answered:
RE: Nozzle cleaning… what’s really going on

It won’t ooze out the print head if the material is not in the melt zone!

Posted : 07/12/2023 7:58 pm
Razor liked
Jeggo
(@jeggo)
Estimable Member
RE: Nozzle cleaning… what’s really going on

I made a feature request on Github and it has the status "closed as completed". So this might show up in one on the next versions 😀 

Posted : 11/12/2023 6:50 am
Razor liked
Jeggo
(@jeggo)
Estimable Member
RE: Nozzle cleaning… what’s really going on

Sorry to correct this. Prusa believes this belongs to the firmware. Same as the behaviour with the M601 G-code. While the printer waits for your interaction, the tool stays over the print bed and oozes out filament, that is later smashed into the print object. This sure is a firmware thing.

I tried to explain this. Especially when I print with PETG, more than 50% of the time, the nozzle cleaning after the heat absorbtion fails. With other filaments this might not be such a big problem. My patch cures the problem so far and works well.

It it also not necessary to have the tool picked during heat up of the print bed. But it is not a big think, as the print head stays at 170°C and more or less no filament leaves the nozzle.

Posted : 11/12/2023 8:20 am
Tobycwood
(@tobycwood)
Estimable Member
Topic starter answered:
RE: Nozzle cleaning… what’s really going on

I do not see the behaviors you are describing. If the material is left in the melt zone while parked some will still ooze down and if it does it touches the nozzle sealer. When the tool is picked up the stuff that touches the sealer sticks and the tool leaves a string.

Retracting out of the melt zone stops this. If the material all leaves the melt zone then on detraction no priming is needed since the material stays contiguous between tool use. I can get it to work that well with PLA. PETG still needs a prime tower.

Posted : 11/12/2023 4:02 pm
Jograybeal123
(@jograybeal123)
Member
RE: Nozzle cleaning… what’s really going on

After watching this guys video it’s terrible. Sadly someone who doesn’t know what’s going on with his XL for someone to print that many bad prints it’s either an uneducated/bias user or a faulty machine somewhere in the technology. That video is not a good video to watch if you’re serious about the XL. It’s showing one random person who deemed himself a teacher…. Failing at getting quality from a machine that spits out unbelievable results when used correctly. Anyone who knows about this machine knows this guy doesn’t know the machine. Lol it’s super brand new to him in this video. In that he has only been learning how to use it since he got it. He wasn’t an expert prior to getting it and he’s new to learning it just like everyone else…. Only his video shows his knowledge/skill. Is sub par. 

Posted : 11/01/2024 6:24 pm
fuchsr liked
Tobycwood
(@tobycwood)
Estimable Member
Topic starter answered:
RE: Nozzle cleaning… what’s really going on

Dems da Toobers!

Most are clueless, but I've actually seen some of the most respected say some pretty ignorant things too.

It's too bad that there's so many poor performance reports which I believe are directly related to the lack of system level testing for "Fully Assembled" units. I was lucky I guess because all the issues I've run into (so far) I've been able to rectify myself. Toolchangers are WAY WAY more complex then Mendels and to jump from a MkIII to the XL and expect to know what you're doing is really naive. As such, would I recommend a fully assembled XL-5? No. Not until they start shipping them with the extruders attached and after full system level verification on each extruder. I.e., a sample print from each delivered extruder.

Posted : 12/01/2024 9:27 pm
Nikhil S.
(@nikhil-s)
Trusted Member
RE:
Posted by: @jograybeal123

After watching this guys video it’s terrible. Sadly someone who doesn’t know what’s going on with his XL for someone to print that many bad prints it’s either an uneducated/bias user or a faulty machine somewhere in the technology. That video is not a good video to watch if you’re serious about the XL. It’s showing one random person who deemed himself a teacher…. Failing at getting quality from a machine that spits out unbelievable results when used correctly. Anyone who knows about this machine knows this guy doesn’t know the machine. Lol it’s super brand new to him in this video. In that he has only been learning how to use it since he got it. He wasn’t an expert prior to getting it and he’s new to learning it just like everyone else…. Only his video shows his knowledge/skill. Is sub par. 

Just have to add that the whole sales pitch, marketing, price point, and feature set of this machine are explicitly made so that you **don't** have to tweak or learn why your machine is not doing what it is supposed to out of the box. If they can't guarantee a certain level of out-of-box reliability, it's time to reexamine the design and/or the packaging for shipment.

Like it or not, this is 2024, and expectations for premium-priced printers are a LOT higher than even 1-2 years ago. And, let's be clear, their marketing is overselling it. But that's business, if you say it does it perfectly every time, it damn well better.

Brand new to 3D printing and my 5-tool XL is my first 3D Printer! I have done massive amounts of research though, so I'm not starting completely from square one....

Posted : 15/01/2024 9:08 pm
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