First layer adhesion

I have a metric f**kton of "budget" PLA from a UK supplier that I'm starting to regret buying, but as I have so much of it I want to work out some settings for it so that I can use it for prototyping stuff.

The problem I'm having is that I've tried first layer extruder temps from 180 up to 210 and bed temps from 75 up to 100 and it's still hit and miss whether that first layer sticks. The initial skirt and perimeter is usually fine, bar a tiny bit of blobbing on the start/end point. However when when it fills then that first layer I can see the ends of each stroke lift up. Sometimes these little raised "fingers" get squashed down on the next pass and sometimes they don't. Sometimes they catch on the second layer instead. Once I'm above that second layer though, I can usually leave it going with no problems. The print is stuck fast to the bed at the end of the job and I have a bladed scraper for helping me tease it off and I can see that the first layer is barely stuck together - I don't get that glass-like flat finish.

This doesn't seem to be a problem with the Faberdashery PLA, just this cheapo stuff. Any ideas what I should be tweaking? Do I need MORE heat for that first layer? I dabbled with dilute PVA solution which worked for a bit, but made a mess of my bed. I'd really like to print without it if at all possible (until I get some spare glass, I suppose!)

Suggestions welcome!

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I can see that the first layer is barely stuck together - I don't get that glass-like flat finish.

Seems like the first layer is being extruded too high then, or the flow rate is too low on that layer only.

If correcting that doesn't fix it then a high bed temp for the fist layer and then lower afterwards helps. Extruding with a bigger width / layer height ratio will also stick better as the plastic more squashed against against the glass.

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[www.hydraraptor.blogspot.com]

I've recalibrated the bed (it was 0.6mm lower than my initial measurement - probably due to my discovery that the Y-axis clamps weren't actually tight! Oops! ) and made the first layer squish down into the glass.

I get that nice smooth finish now and the little standy-up "fingers" are gone, but I'm now getting a slightly different problem; my unattended ooze-free start code puts the nozzle down at the front left, heats up the bed/extruder, then does a fast wipe across the front before starting on the skirt. This fast wipe is now "rolling" the build-up of PLA to the side of the nozzle, leaving a molten globule that *just* big enough to foul the first layer. In 9 out of 10 prints this now drags the first layer up before it has managed to cool. If I'm quick I can grab it off with a pair of tweezers before it finishes the skirt but that's hardly an unattended start lol!

I don't know why that would be. The blob sticks to the glass rather than the nozzle for me. Maybe the glass needs cleaning at the point.

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[www.hydraraptor.blogspot.com]

I use a window scraper to clear any residue after each print and IPA to clean the entire glass to a squeak before each print, to ensure there is no grease from my fingers lingering around but it doesn't seem to help. Dilute PVA works, but then it makes a mess and eventually chips of glass start coming off...

I've now got my block point at Z0.05 X50 Y95, which is 0.05mm above the bed at the front left. The blob used to stay there when Z_MIN was 0.6mm higher up, so I think I'll try moving my block point back up a bit. I get less ooze now so maybe that's why - there's just not enough to stick fast.

To be honest I'm pretty sure this cheap PLA I have is part polylactic-acid and part polylactic-teflon, because it sticks to nothing.

Every once in a while though I get a serviceable print, which lures me into thinking I can do something useful with it. I can't wait to get back to the Faberdashery stuff.

I found IPA reduced adhesion for me. It seemed to leave a white residue. Not sure if it was something in the IPA or something it dissolved out of the cloth I was using. Vinegar is recommended but I have never tried it myself. I just use acetone as I have loads of it for ABS.

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[www.hydraraptor.blogspot.com]

Interesting. I wonder if the purity is a factor. Mine says 99% pure IPA but then I can't find anything of a lower concentration on eBay so I'm not even sure it's possible to get anything like that.

I don't see any white residue on my glass - but I know when I've used acetone to "clean" PLA in the past then it turns my PLA white really fast. I'll try acetone again and maybe white vinegar too. I'm not particularly looking forward to the smell of either!

I've just also noticed that the area around my nozzle is quite dark, and corresponds to the area that is in contact with the blob that oozes out during warm-up. It doesn't look like residue so is it oxidisation of the brass? Could this be making the PLA stick to it and cause the blob to get dragged around? I do notice that the blob tends to have a bit of darker colouration in it during the initial wipe, but I only heat the extruder to 200 for the first layer and I only wait for 60 seconds for the nozzle to settle so I don't think it's long enough to degrade.