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[Solved] Filament catches on the nozzle during printing  

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WCunningham
(@wcunningham)
Active Member
Filament catches on the nozzle during printing

So, this has been a thorn in my side for some time now. When I print anything, even run a first layer calibration, the extruded filament will seem to jump, and catch onto the edge of the nozzle. I've ran a cold pull procedure several times, chemically cleaned the nozzle (which seemed to help for about a day before the problem returned), and tried clearing the nozzle with the supplied acupuncture needle. Nothing seems to be helping, not even lowering the Z-distance from the nozzle to the bed. Any suggestions or solutions are appreciated. COVID-19 has me stir crazy not being able to print things.

Best Answer by bobstro:

Posted by: @warhammer-kombatant

So, this has been a thorn in my side for some time now. When I print anything, even run a first layer calibration, the extruded filament will seem to jump, and catch onto the edge of the nozzle. I've ran a cold pull procedure several times, chemically cleaned the nozzle (which seemed to help for about a day before the problem returned), and tried clearing the nozzle with the supplied acupuncture needle. Nothing seems to be helping, not even lowering the Z-distance from the nozzle to the bed. Any suggestions or solutions are appreciated. COVID-19 has me stir crazy not being able to print things.

This is a good time to master your printer. Here's an info dump to get you going...
 
The filament doesn't "jump" up to the nozzle. The filament gets squirted out the nozzle and has no way of moving itself. What is happening is that your extrusions are either coming partially loose, causing them to move around as the printer continues to extrude (eventually being snagged by the moving nozzle), or completely loose, leaving the printer extruding in free air (creating the spaghetti). Your underlying issue is bed adhesion. This is a common problem that can be caused or aggravated by two factors that need to work together well for successful prints. Here's mama's tried and true copypasta recipe to get you going...
 
You are having bed adhesion issues. Filament should lay down cleanly on the PEI print surface and hold throughout the print. There are 2 main causes of bed adhesion issues. Even if you're dubious that these are the cause of your problems, they're 2 fundamental troubleshooting steps that you need to complete to rule out the basics:
  • A dirty PEI print surface. Even if you don't think this is the cause, it's always a good idea to make sure your PEI surface is clean before trying any other fixes. If it's a smooth PEI sheet, take it to the kitchen sink and give it a good dunk with Dawn (original formula, no vinegar or hand softener variants) dishwashing soap or your local equivalent (e.g. Fairy in UK). Use a clean paper towel to clean it off, and another to dry it. Avoid using any sponge or cloth that has been in contact with grease. Above all else, avoid touching the PEI print surface. Once it's good and clean, you should be able to use 91%+ isopropyl alcohol between prints, 100% acetone when that fails , and another dunk when acetone fails. Worst-case, use a 3M 7445 ScotchBrite pad or equivalent on smooth PEI to give it a very light buff, but only infrequently. If you've got a textured powder-coated PEI print surface, the official instructions are to use 91%+ isopropyl alcohol on it only. Rumors persist that some tribes deep in the jungle have had good luck getting started with these sheets by giving them a wipe with 100% acetone and a dunk with Dawn. Either way, there's no real warranty on these sheets. YMMV.
  • If you have not already done so, try using Jeff Jordan's "Life Adjust" procedure for calibrating your Live-Z setting. It is much easier to use and understand than the on-board routine and much easier to make mid-print adjustments accurately with. In general, start high (less negative) and work lower (more negative) in large increments (e.g. 0.1mm) until the filament starts to stick on its own. When you've got your Live-Z setting adjusted properly, you should be able to gently rub the extruded lines on the PEI surface without dislodging them.  Then start lowering (more negative) the level until there are no gaps between layers. You should not be able to peel the lines apart after printing, but the top should be regular. 
Remember that the effectiveness of a solvent such as isopropyl alcohol is going to depend on concentration and volume relative to the amount of grease you're trying to remove. 71% pads work... on very tiny amounts of grease. A squirt of 91% works better, but if there's a lot of grease, you need a lot more alcohol. This is why the wash under the sink with Dawn is so effective: There's a much larger volume of Dawn-and-water rinsing stuff away instead of just moving the broken-down grease molecules around.
  
And above all else, avoid touching the PEI print surface.
 
Glue stick is NOT necessary for PLA on the PEI print surface. You paid the big bucks for a Prusa with a removable spring still sheet with PEI, so clean it up and take advantage of it. Save the glue stick for printing sticky stuff like PETG that might adhere too well. Even then, I only find I need glue stick when printing high-temp PETG at 260C+ temps.
 
Try those 2 steps. If you're uncertain of the Live-Z results, post pics here of the 75x75 print bottom and you'll get quick help. If you want more detail, I've consolidated my notes on Prusa PEI adhesion, bed cleaning, and Live-Z calibration
 
A bit of trivia - The reason higher concentrations of alcohol seem to be harder to find is that isopropyl alcohol is most effective against bacteria at roughly a 71% concentration. A bit of distilled water helps slow evaporation, making the alcohol more effective. If you're looking in pharmacies, that's why 91% and higher seem to be hard to find.
 
This topic was modified 4 years ago by WCunningham
Posted : 03/05/2020 2:33 am
WCunningham
(@wcunningham)
Active Member
Topic starter answered:
RE: Filament catches on the nozzle during printing

EDIT: The filament catches on the nozzle frequently, but there are instances when it will not. It will jump onto the nozzle edge, then jump back onto the build plate. But if say, I'm printing supports where the axis makes repeated up and down movements, the filament will simply build up on itself, making a bad extruder blob.

Posted : 03/05/2020 3:15 am
JoanTabb
(@joantabb)
Veteran Member Moderator
RE: Filament catches on the nozzle during printing

if you are printing PETG, try reducing the Flow Rate to say 90%

If the printer is slightly over extruding, PETG tends to get picked up on the  nozzle where as with PLA the nozzle  tends to push the filament out of the way. 
If you are slicing your own models try making the extrusion multiplier 0.95 instead of 1, for petg... 

regards Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK

Posted : 03/05/2020 9:46 am
OZ1BMO liked
WCunningham
(@wcunningham)
Active Member
Topic starter answered:
RE: Filament catches on the nozzle during printing

@joantabb

Thanks, but I'm using PLA filament. Probably should've clarified that.

Posted : 03/05/2020 3:54 pm
bobstro
(@bobstro)
Illustrious Member
RE: Filament catches on the nozzle during printing
Posted by: @warhammer-kombatant

So, this has been a thorn in my side for some time now. When I print anything, even run a first layer calibration, the extruded filament will seem to jump, and catch onto the edge of the nozzle. I've ran a cold pull procedure several times, chemically cleaned the nozzle (which seemed to help for about a day before the problem returned), and tried clearing the nozzle with the supplied acupuncture needle. Nothing seems to be helping, not even lowering the Z-distance from the nozzle to the bed. Any suggestions or solutions are appreciated. COVID-19 has me stir crazy not being able to print things.

This is a good time to master your printer. Here's an info dump to get you going...
 
The filament doesn't "jump" up to the nozzle. The filament gets squirted out the nozzle and has no way of moving itself. What is happening is that your extrusions are either coming partially loose, causing them to move around as the printer continues to extrude (eventually being snagged by the moving nozzle), or completely loose, leaving the printer extruding in free air (creating the spaghetti). Your underlying issue is bed adhesion. This is a common problem that can be caused or aggravated by two factors that need to work together well for successful prints. Here's mama's tried and true copypasta recipe to get you going...
 
You are having bed adhesion issues. Filament should lay down cleanly on the PEI print surface and hold throughout the print. There are 2 main causes of bed adhesion issues. Even if you're dubious that these are the cause of your problems, they're 2 fundamental troubleshooting steps that you need to complete to rule out the basics:
  • A dirty PEI print surface. Even if you don't think this is the cause, it's always a good idea to make sure your PEI surface is clean before trying any other fixes. If it's a smooth PEI sheet, take it to the kitchen sink and give it a good dunk with Dawn (original formula, no vinegar or hand softener variants) dishwashing soap or your local equivalent (e.g. Fairy in UK). Use a clean paper towel to clean it off, and another to dry it. Avoid using any sponge or cloth that has been in contact with grease. Above all else, avoid touching the PEI print surface. Once it's good and clean, you should be able to use 91%+ isopropyl alcohol between prints, 100% acetone when that fails , and another dunk when acetone fails. Worst-case, use a 3M 7445 ScotchBrite pad or equivalent on smooth PEI to give it a very light buff, but only infrequently. If you've got a textured powder-coated PEI print surface, the official instructions are to use 91%+ isopropyl alcohol on it only. Rumors persist that some tribes deep in the jungle have had good luck getting started with these sheets by giving them a wipe with 100% acetone and a dunk with Dawn. Either way, there's no real warranty on these sheets. YMMV.
  • If you have not already done so, try using Jeff Jordan's "Life Adjust" procedure for calibrating your Live-Z setting. It is much easier to use and understand than the on-board routine and much easier to make mid-print adjustments accurately with. In general, start high (less negative) and work lower (more negative) in large increments (e.g. 0.1mm) until the filament starts to stick on its own. When you've got your Live-Z setting adjusted properly, you should be able to gently rub the extruded lines on the PEI surface without dislodging them.  Then start lowering (more negative) the level until there are no gaps between layers. You should not be able to peel the lines apart after printing, but the top should be regular. 
Remember that the effectiveness of a solvent such as isopropyl alcohol is going to depend on concentration and volume relative to the amount of grease you're trying to remove. 71% pads work... on very tiny amounts of grease. A squirt of 91% works better, but if there's a lot of grease, you need a lot more alcohol. This is why the wash under the sink with Dawn is so effective: There's a much larger volume of Dawn-and-water rinsing stuff away instead of just moving the broken-down grease molecules around.
  
And above all else, avoid touching the PEI print surface.
 
Glue stick is NOT necessary for PLA on the PEI print surface. You paid the big bucks for a Prusa with a removable spring still sheet with PEI, so clean it up and take advantage of it. Save the glue stick for printing sticky stuff like PETG that might adhere too well. Even then, I only find I need glue stick when printing high-temp PETG at 260C+ temps.
 
Try those 2 steps. If you're uncertain of the Live-Z results, post pics here of the 75x75 print bottom and you'll get quick help. If you want more detail, I've consolidated my notes on Prusa PEI adhesion, bed cleaning, and Live-Z calibration
 
A bit of trivia - The reason higher concentrations of alcohol seem to be harder to find is that isopropyl alcohol is most effective against bacteria at roughly a 71% concentration. A bit of distilled water helps slow evaporation, making the alcohol more effective. If you're looking in pharmacies, that's why 91% and higher seem to be hard to find.
 
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 : 04/05/2020 5:28 am
WCunningham
(@wcunningham)
Active Member
Topic starter answered:
RE: Filament catches on the nozzle during printing

@bobstro

Ah how archetypal. We Mechanicus always favor overly complicated solutions over the most basic and simple ones; praying machines to work with burning incense and overlooking the obvious solution.

Thank you very much. Cleaning the printing plate worked like a charm. Thank you so much for the help. I really appreciate it.

Posted : 05/05/2020 1:20 am
bobstro
(@bobstro)
Illustrious Member
RE: Filament catches on the nozzle during printing

Glad you got it fixed. Happy printing. 

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 : 05/05/2020 1:27 pm
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