Warping and Artifacts on flat surfaces

[davealdon 0]

Hello! I’ve been printing things with small surface areas directly on the glass without issue. But when I print something with a larger, flat area I’m seeing warping in the middle parts, and random lines all over. I’m wondering what I can do to help reduce this, and have a great, smooth surface directly on the glass?

 

I included a couple pictures to show what’s happening. This is “Generic PLA” settings in Cura and the machine. I see this with any brand. 
 

Thank you so much!

[geert_2 558]

If this is on the bottom of the print (=touching the glass), or a very thin print of only 1 or 2 layers, I would suspect grease or oil on the glass, so it does not stick and lifts off. But if this is on the top of a thicker print (hard to see on photo), it is something else: maybe too little infill, or a too thin top surface?

 

For this sort of things, you could best watch closely while printing: often you can see what is happening, and why. For example, if there would be oil on the glass, you can see how the filament does not stick in certain areas and is dragged around. Or you can see material accumulating on the nozzle, and being deposited on the print, and all sorts of other irregularities.

 

[davealdon 0]

Interesting. These aren't thin prints, I see the artifacts on every bottom layer. I'll try cleaning it more rigorously to see if there's oil like you say. Thank you.

[Smithy 1,144]

Wipe it with Isopropyl alcohol and I would also use a very thin layer of glue on the bare glass. Do just 3-4 stripes and then distribute it with a wet towel until you get a thin but even layer.

[davealdon 0]

But would I still be able to get the same smooth surface with even a thin layer of glue? I use it on some things, but it makes the surface pretty ugly. I feel like there's other issues going on that glue bandaids.

[Smithy 1,144]

No, not as smooth as when you just print on bare glass. 

Maybe just try to wipe it with IPA, maybe this is already enough to solve the problem.

[nallath 1,123]

Those kind of artifacts can also occur if your first layer is too close to the buildplate.

[LePaul 328]

Like @nallath says, it has been my experience that if you see those little waves, you can either be a tad too close or a bit too warm on your nozzle temp.  Or both!  I hope this helps you dial it in

[geert_2 558]

In the beginning I used the glue stick (without wiping it afterwards, I didn't know that trick back then). But this gave an ugly bottom layer indeed, and non-optimal bonding. I also tried printing on bare glass without any glue: in dry weather this would work reasonably, but in wet weather it would lift off and cause defects like yours. Also, greasy glass would cause this effect. Cleaning with soap and window-cleaner can also produce this, since soap reduces bonding: you can't glue anything to soap.

 

So, now I thoroughly degrease the glass first, and then wash it with pure luke-warm tap water only (no soap, no window-cleaner, nothing). And then I wipe it with a tissue moistened with salt water: this also improves bonding of PLA to the glass bed when hot, but the print comes off by itself after cooling down. For in case you want to print on bare glass, without glue, like me. If you would prefer using glue, dissolve it and spread it out evenly with a wet tissue, until it is an almost invisible thin layer.

 

As others said above, also check the nozzle-distance from the glass. If too big, there is not enough contact and the print is likely to lift off. If too close, the nozzle may scrubb the print off the glass, also lifting it off.

 

The bottoms of my prints usually look like this:

 

Bottom layer, and reflection in the bottom layer (could not get both in-focus at the same time):

 

PLA print, nozzle is 0.4mm, the round hole is ca. 4mm diameter:

 

PET-print, thin layers, ruler in the background is in mm and cm: