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First layer snagging problem  

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renee.m
(@renee-m)
Eminent Member
First layer snagging problem

Any suggestions on how I can get it to stop doing this on the first layer of my larger prints?

I have done several z-axis calibration tests, and have it well calibrated.

If I print something smaller, then it prints the first layer just fine. But when I'm doing a really large print, this happens.

Settings for this print:

  • Layer height: 0.25mm
  • First layer height: 0.25mm
  • First layer speed: 40mm/s
  • Extruder Temp: 210
  • Bed Temp: 95 (first layer) 80 (other layers

I have experimented with Bed Temp, it used to be 70, but I found I got better cohesion with a higher first layer bed temp, and the problem improved on smaller prints, but is still an issue on large prints. I have a disc with a 12cm dia, and it prints perfect, every time with the above settings. 

Thanks

 

Posted : 14/05/2019 12:33 pm
Vojtěch
(@vojtech-3)
Honorable Member
RE: First layer snagging problem

Does it do the same on both sides of the sheet? Is the sheet clean? How about when you print slower (simply use the dial next to the screen while printing). What material? 95 is way too much for PLA, it'll never harden at that temperature.

Posted : 14/05/2019 1:43 pm
renee.m
(@renee-m)
Eminent Member
Topic starter answered:
RE: First layer snagging problem

Hi,

Thanks for the feedback. 

Yes, happens on both sides of the sheet, and I clean it regularly. Cleaned it (with Isopropanol) right before this print. 

Didn't know I could adjust the speed on the fly like that, very cool! Will give it a try.

I agree, 95 degrees is hot for PLA (which is what I'm using). But it seems to do it less when it's hotter. 

I'll do some more testing and post the results. I'll vary the temp and speed of the first layer with some different sized prints. 

Thanks. 

Posted : 14/05/2019 2:03 pm
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(@)
Illustrious Member
RE: First layer snagging problem

This is classic bed contamination; your first photo even shows a clear set of fingerprints.  Have a look at the photo I attached, the lack of adhesion was 100% contamination.

Also, as Voj has said, while you can get away with a thicker first layer, 0.20 is the recommended height based on lots of experience, and printing a 0.20 layer at faster than 20 mm/s is difficult because the speed of the extruder and surface tension of the plastic will pull the extruded plastic back up.  And 60c is really all you want for laying down PLA.  There are times 70c is useful, but those are rare.

Back to bed contamination: Alcohol is NOT a good routine cleaning solution for PEI sheets.  It's great for touch up, but when the bed is dirty you simply can't get enough alcohol to rinse away the oils - and worse - unless you use gloves it strips your fingers of oil, hand lotion, and anything else that happens to be on them and can actually make the bed dirtier.  Some people have access to industrial sized containers of alcohol and can wash the bed in it;  most of us only have a liter bottle, or less, so we use it sparingly - and can't use the half cup needed to actually begin to wash then rinse properly. 

Use soap and hot water. Here's a recipe that works every time.  Feedback I have received from others like yourself indicates it works for them and restores the bed to like new condition.  If you use alcohol or acetone, do the soap and water wash last to rinse off what the chemical knock loose.

Hot Water wash: often, as needed
Handle the bed only by the edges.
Wash the bed in hot water, use a fresh paper towel as a wash cloth, with a few drops of plain dish soap (Dawn, unscented, no anti-bacterial, etc.). Rinse well in hot water - if you have very soft water, rinse a bit longer.
Dry the bed with a fresh paper towel.
Handle the bed only by the edges.
Place bed on printer.

Alcohol rinse: every few prints
Once in a while, an alcohol rinse is helpful to remove PLA residue. It does not remove finger oils.
Pour a 5 cm puddle of 91%+ alcohol in the middle of the bed, with clean hands use a fresh paper towel to scrub the bed. Wipe up all the alcohol.

Streak test: when contamination is suspected
With a fresh piece of paper towel, and very clean fingers, dampen the towel with 91%+ alcohol, and wipe the bed side to side moving back to front, like you're painting it with alcohol. The alcohol should be thin enough on the towel it quickly evaporates. If you see any streaks, the bed is dirty and needs a wash.

Acetone wash: infrequent
Pour a 2 cm puddle of acetone on the bed, scrub it around with a fresh paper towel. It will evaporate fast as you clean. This step removes PEI oxides that form over time and with heat, and improves PLA adhesion to a like new state.

Posted : 16/05/2019 7:52 am
Peter M
(@peter-m)
Noble Member
RE: First layer snagging problem

And in sl3r the first layer speed should be 20 mm, so you are 2x as fast.

Cleaning, very important

first layer live adjust, very important.

 

if it does not work,

slower(then 20 mm)

hotter is better

different filament

big flat parts i use glu stick, then even pla i have sometimes curling, glu stick is not needed fort the first layer not sticking.

Posted : 16/05/2019 8:53 am
renee.m
(@renee-m)
Eminent Member
Topic starter answered:
RE: First layer snagging problem

Thanks Tim & Peter, awesome advice!

A good wash with soap seemed to really help, and such a simple solution. 

After the wash, I started a fresh print with these settings:

Bed temp: 60ºC

First layer height: 0.20

First layer speed: 20mm/s

And this is the result. 

I had carried out a number of tests yesterday on a couple different designs, changing speed and bed temp, and what puzzled me was that it printed fine up to a certain point, around the same spot on the bed. Which makes me think a big part of the problem was oil on the surface. 

Thanks again for all your help.

Posted : 16/05/2019 11:51 am
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