Material and color dependent adhesion
Like many parent's, I've been printing among us characters. That meant printing the same files, often the same programs, with different colors. I noticed that I can run a program with one shade of PLA, and everything be absolutely fine, switch to a different shade of PLA, and find that the first layer does not want to stick. The defects looks like a Z0 problem, except that it absolutely does not respond to z0 tuning, and besides, if it printed fine from a different spool, why would changing spools affect Z0?
What it does seem to respond to is extruder tensions (I'm doing all this on mk3s mmu2s in single mode if that's important to anyone). Roughly speaking, materials that are more bendy (are not galaxy types with filler in it, the filament can be bent on a tighter radius before it breaks) seem to need the extruder tension screw backed up a few turns, or else they don't seem to want to stick. The same setting on the harder materials (galaxy filled, more brittle stuff, especially galaxy black) means insufficient tension and skipping at the extruder.
Of the PLAs I have, prusament lipstick red seems to be the hardest to get to stick and likes to peel up (looks like this https://photos.app.goo.gl/w3vJz22LSoZLSFZ46)
Of the PETG, pistachio green was really resistant to sticking, I ended up printing it on the smooth sheet because it really did not want to stick to the textured, while the chalky blue petg was the record holder for sticking and made me wonder if I was going to damage the sheet getting it off. All in all, I tried 10 different filaments, mostly prusament, but some hatchbox as well (hatchbox silks are really easy to work with).
I have a theory as to what is going on, that I wanted to run by those of you who have more experience in this than I do.
The problem of hard filament combined with low extruder tension seems pretty simple, the gears just aren't digging in enough to provide sufficient traction on the filament. In the reverse case (softer filament/high tensions) I think the gears are biting in deeper, reducing the diameter and effective circumference around which the filament is fed. This pushes slightly less filament for every extruder step, in effect reducing the flow. I don't know why reduced flow would result in poorer first layer adhesion. Maybe the layer is thinner and has more stress in it that pulls in more? Maybe the lower flow means the material gets a little hotter going to the hot end?
If anyone ran into this sort of thing before and knows more about it, I would really appreciate knowing more.
RE: Material and color dependent adhesion
First layer adhesion is achieved by getting the right amount of filament to fill the gap between the nozzle and the bed, with just enough excess to cause adjacent lines to fuse together.
If your observations are correct, you are getting different performance from different materials, however nothing is particularly easy in 3D printing
So
if you did your Live Z setting with the soft filament with reduced feed, then the hard filament may over extrude and this may cause buckling of the contact layer and reduced adhesion.
On the other hand
If you did your live Z with the hard filament then when you use the soft filament you might get reduced adhesion because you have insufficient squish...
however you may find that your bed temperature is wrong for some of the filaments and that also may give you reduced adhesion
And some of the filaments may simply be more sticky than the others...
You have found a Mega Sticky PETG... next time you forget to use something like windex as an adhesion limiter with that filament, try dribbling a little IPA around the base of the model, on the cool build plate, let it sit a while, hoping that it will infiltrate the PEI/PETG Bond area and you may well find the part pops off without too much effort or damage tot he PEIR (This usually also works for TPU/TPE)
going back to your initial issue, PETG and PLA Often need different Live Z settings. to get good adhesion.
different filament rolls can have different performance even between different rolls of the same colour from the same manufacturer.
I have had PLA that strings like crazy above 170C, I have PLA that needs to print at 220C or the inter layer bond goes to pot...
I ordered a roll of PLA in a sparkly red colour, when it arrived I was disappointed by the poor adhesion, curling and poor surface finish... then I looked at the label to see if there were special temperatures I was supposed to use. and that's when I noticed that I had been supplied Sparkly red PETG... using a PETG profile, was much more successful.
Some folk print test models, or test swatches, or temperature towers with new rolls of filament to see how they behave.
additionally your differing flow rates for hard and soft filaments may need different printing temperatures to obtain the expected flow...
If you find that a filament needs different handling, it is wise to mark the reel, so you remember, next time.
I tend to print PLA with a bed temperature of 70C, although I have seem filaments recommend 80C for PLA...
You need to observe how your printer handles different filaments and if necessary, make notes for future reference.
Have you also noticed that Textured and silk build plates require a larger live Z value than Smooth PEI Build plates?
regards Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK
RE: Material and color dependent adhesion
I hear you, but look at this. I created a model of a 20mmx20mmx1mm square, put several of them in a file, and live changed z0 between each square. Take 1.
https://photos.app.goo.gl/ZXcpeD6GwcsHD4pbA
That's about what you'd expect, -1.0 seems too much squish, -0.75 seems far too little, and the best results are somewhere between -0.9 and -0.85, right?
So, I try it again (same material, same sheet, just freshly cleaned with IPA). Changed the file to give myself a bit more space between the squares, and got this:
https://photos.app.goo.gl/fvc9GnpWFZMGVbMx5
It's hard to call anything here best, right? Things just aren't sticking. Tried a few more times, starting with numbers from -0.8 to -1.0, but I couldn't even take pictures because nothing stuck at all. Cleaned the sheet between each try with IPA.
Let's go back to the original file. Clean, let's use the same numbers as before. Nothing sticks. Clean again, try again. Got this
https://photos.app.goo.gl/p3LATxBgyytTzrWc8
Same material, same temperatures, the first and last pictures are the exact same print file. If this was a z0 issue, I would have thought the first and last picture would have looked the same.
For reference, This is prusament lipstick red pla, 210C nozzle, 60C bed temp