Notifications
Clear all

First layer, nozzle drags line starts along for a few mm  

  RSS
DarthRaptor
(@darthraptor)
New Member
First layer, nozzle drags line starts along for a few mm

Hello,

I've had my Mk3S+ for a few weeks now, printing beautifully. But now I've developed a problem that I am so far unable to solve.

When the print starts, the first line layed down for an object get's dragged along for a few milimeters, it doesn't adhere. Especially when printing small circles, often the first of the two perimeter lines gets dragged along. I've spend an entire day trying to calibrate the live z, also doing the bed level correction procedure (that was worth it though, improved the first layer on the corners of the bed massively). I've anything my live z is a bit too close to the bed, but if I raise it, this line start problem get's worse. I've had two print failures so far due to this, since small objects didn't adhere.

I'm cleaning the steel sheet with isopropanol alcohol before every print, and I've now tried the completely unused other side of the sheet with no success. What's weird is that the skirt line adheres without a problem (usually even with a small blob at the line start). I've also noticed that the problem is worse if the printhead has to do a longer travel move to the next line.

Any tips on what settings to try adjusting are welcome.

Posted : 28/08/2021 3:50 pm
bobstro
(@bobstro)
Illustrious Member
Bed adhesion blues
Posted by: @darthraptor

[...] When the print starts, the first line layed down for an object get's dragged along for a few milimeters, it doesn't adhere. Especially when printing small circles, often the first of the two perimeter lines gets dragged along. I've spend an entire day trying to calibrate the live z, also doing the bed level correction procedure (that was worth it though, improved the first layer on the corners of the bed massively). I've anything my live z is a bit too close to the bed, but if I raise it, this line start problem get's worse. I've had two print failures so far due to this, since small objects didn't adhere.

Assuming your Live-Z calibration is good (post a pic of the underside of a print to verify), you most likely are suffering from simple adhesion issues. This is common and the PEI sheets are a bit different than most other surfaces. You didn't mention whether you're using a smooth, satin, or textured PEI sheet. The textured can be a bit tricky to use with PLA.

I'm cleaning the steel sheet with isopropanol alcohol before every print, and I've now tried the completely unused other side of the sheet with no success.

I'm going to post a big dump of "everything you need to get started with the PEI sheet". Read through this, feel free to ignore bits, but pay attention to the cleaning of the PEI. First and foremost, it is possible to excellent first layer results with the PEI sheets.

Here's the info dump on dealing with the bed adhesion blues...

Your underlying issue is bed adhesion. Bed adhesion should be strong enough to hold the print flat and securely against  the forces of filament warping and nozzle friction. Filament should lay down cleanly on the PEI print surface and hold throughout the print.  If adhesion is poor, your print is likely to fail or have problems at higher layers. Common adhesion-related problems include:
 
  • Part warping or lifting along edges.
  • Bumping or knocking noises as the part moves under the nozzle.
  • Uneven vertical surfaces and bulges caused by print lifting and compression of overlying layers.
  • Spaghetti resulting from parts moving during printing.
  • The dreaded "blob of doom" caused by the part lifting and sticking to the nozzle as it extrudes filament.
 
There are 2 main causes of bed adhesion problems: cleanliness of the PEI print surface and Live-Z height adjustment. Even if you're dubious that these are the cause of your problems, they need to be addressed as 2 fundamental troubleshooting steps 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 (1200-1500 grit) 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 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.
  • Improper Live-Z adjustment. If you have not already done so, try Jeff Jordan's "Life Adjust" procedure for calibrating your Live-Z setting. It is much easier to use and understand than the onboard 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 a wash under the sink with Dawn is so effective: There's a much larger volume of Dawn-and-water attaching to grease and 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.
 
If, after doing all this, you still find narrow or tall parts popping off or warping you might try adding mouse ears to corners and thin parts,  adding a brim, or applying some additional adhesion booster to your bed. I'd go in that order for best consistency and ease of cleanup.
 
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 : 28/08/2021 6:37 pm
DarthRaptor
(@darthraptor)
New Member
Topic starter answered:
Thank you

I am indeed using the smooth PEI sheet, sorry that I forgot to mention that. I think you're right about the sheet being dirty, I found another post mentioning the volume of alcohol used (I have 99%  concentration btw) and before I was just dampening a paper towel slightly with it. So for my last print yesterday, I drizzled a few ml onto the sheet, let it soak and then wiped it off, making sure to wipe away from the center.  While the next print wasn't perfect, it was way better then any print I've gotten in the last few days.

I'll try that live Z procedure. While I'm pretty sure my live Z is good, I've never thought to check if it's actually 0.2mm thick. But I did try to pull the lines apart and I can't the layer is completely fused together and has more of less smooth surfaces top and bottom.

 

Thanks a lot. My only previous experience with 3D printing was my Dad's Anycubic Kossel with a glass print plate, and that thing was extremely sticky once up to temp and there's no need to worry about scratching it or grease. As long as the heatbed was still warm, you would not get the prints off. However I did have a lot of warping problems with that one, which I have not experienced with the Prusa so far.

Posted : 29/08/2021 7:55 am
Share: