Why do some prints stick and others don't?

[Canned_Soop 0]

Some of my prints stick to the plate just fine, others won't at all. II've tried every base available, I've tried the glue stick method. I've tried starting a print that I know will stick, see that it sticks. Aborted it, and then started the print I wanted. Still won't stick. What am I doing wrong? I am also completely new to this and appreciate any advice.

[dmitche3 0]

Here are several reasons.

1.  Your print bed is dirty.  Left over dust from a print or oils from fingers can cause problems.

2.  You have a heated bed but you don't allow the bed to heat up to the temperature that you set.  Eventhough the readout on your printer says 60C it can take five minutes or more before a glass bed will actually get to that temperature.  If you start printing and have issues that disappear after several failed print attempts think of this.

3.  Your printer bed isn't quite leveled.

4.  Your filament is a bit on the wet side.  In your case, this is probably not your issue, yet.  I strongly recommend a filament dryer. I use an older Sunlu version 1.  I say that 80% of the filament I buy from Microcenter is wet. Don't be fooled by vacuum sealed bags as when the filament is made from large vats and then is rolled into very large diameters and placed on very large reels and stored.  At this time the filament can get waterlogged.  Factories don't use air-conditioning and such.  The filament is then put extruded into the 1.75mm, 2.85mm or larger size diameters as customers need it and THEN it is sealed into their vacuum bags and a desicate package added.  Too late though.

Edited April 27, 2022 by dmitche3
added some clarification

[bappi 0]

Wash your glass bed with soap n water dry it and use a fine layer of hair spray my prints never fail to stick and when the prints done if you leave it to cool down a bit they pop right off.

 

[GregValiant 1,251]

If you are leveling manually then another reason can be that the Z switch stop point is inconsistent.  You auto-Home and level the bed with your trusty piece of paper and it's perfect.  You start the print and one of the first things is a G28 and the axes auto-home.  Is Z=0 in exactly the same place in space?  Probably not, and so the gap is different than during leveling.  My Ender could be off by .3 to .5mm high or low.  I changed the G28 in the startup gcode to G28 X Y and it has worked.  I level and then leave the Z where it was.

One way to overcome the first layer problems is to increase the "Initial Layer Flow" to 110% or even 120%.  It's a crutch to do it that way but as you get more consistent at starting prints you can back that off.  I still run first layers at 105% for both PETG and PLA.  I rarely have a problem with first layers and when I do it's almost always because I tried to get one more print out of the bed before I gave it a good scrub.  I like washing with dish soap followed by an alcohol wipe down after the glass is back in place on the printer.  PETG would require hairspray at that point.

Edited May 15, 2022 by GregValiant