Understanding Z offset when using different filaments  

RE:

Hi,

The Z-offset for the first layer will be the same for PETG and PLA unless you change it - PrusaSlicer does not change the value based on the slicing parameters or filament type selected.

Like others, I generally find that PETG requires a bit less 'squish' than PLA, so on my MK3S+, I print PLA at -1.455 and PETG at -1.435. Your optimal values will almost certainly be different to mine.

I'd recommend experimenting a with some one-layer calibration squares to determine the optimum Z-offset values for your specific filaments and sheet. Note that the sheet type (Smooth, Satin or Textured) will also affect the Z-offset values because of the different sheet thicknesses and the actual structure of the surface finish. The good news is that the printer allows you to maintain independent Z-offset values for up to 8 different sheets - just remember to select the right sheet profile when you physically change to a different sheet. You could use this feature to store a sheet/filament combo if you wanted - use one slot for Smooth+PLA and another for Smooth+PETG.

I hope that helps!

Cheers,

Tim

RE:

Thanks. When you say PETG requires a bit less squish, is that because PETG is stickier, and adheres to the sheet more readily?

Also, when PETG is printed with the Z offset that you use -- which means, I gather, the nozzle is raised about 0.02mm compared to the Z offset you use for PLA -- does this affect the appearance or thickness of the printed first layer?

RE:

The general mantra is that PETG doesn't "like" to get squished as much as PLA so live Z would be a bit less negative. I must say that I usually move between PETG and PLA without adjusting Live Z, maybe because it's on the upper end of the PLA spectrum already. 

It's not totally inconceivable that flipping the sheet may require some adjustment, if the coating is not equal on both sides. 

If in doubt you can run a quick calibration (eg. https://www.prusaprinters.org/prints/105404 . Takes only a few minutes and let's you check a range of values up or down from your current live z in one print. 

RE: Understanding Z offset when using different filaments

Posted by: @frank-o-2

For some time now I've been using only PLA filament with my MK3. Yesterday I tried using PETG for the first time.

I only have a smooth PEI sheet, so I flipped it over and cleaned it with window cleaner (keeping the other side of the sheet for use with PLA, cleaned with isopropyl). In PrusaSlicer I selected Generic PETG for the filament, and 0.15mm Quality for the print setting, but otherwise made no changes.

While the first layer was printing, I wondered if the nozzle was too high, as the lines of filament appeared as though they might be loose. However, when the job was done the finished object looked pretty solid. It was somewhat harder to remove than a PLA object, but not a big deal.

So I'm wondering: When I chose Generic PETG as the filament in PrusaSlicer, does this cause the first layer of the print to be at a greater height -- to counteract the fact that PETG is stickier than PLA?

 

The answer is no. you were right to added the window cleaner preferably "Windex original" to your smooth PEI sheet. Aside from that I make no adjustments for PETG at all, now with this said, you need to look at your individual setup, I know it seem counter intuitive, however you need to learn what is right for your individual setup, you can take advice from, and learn from, other persons settings but you need to learn to adjust these settings based on your very personal setup. even when using the same printer, you may have your Z set slightly different to the person your taking advice from and this can change things on your end. you must learn to temper that, knowing your setup, filament type & brand.

Just my experience, relative to these forums, good luck.

Swiss_Cheese

RE: Understanding Z offset when using different filaments

Wise words from Swiss_Cheese! We offer advice based on our own learnings but it is really just guidance to direct you along your own learning path.

If the truth be told, I sometimes forget to alter the Z-offset when changing between PLA and PETG. There is very little difference in the resulting first layer quality, but I have found that going 0.02 higher for PETG seems to reduce the chance of material collecting on the nozzle and later getting pulled off onto the print as a 'blob'.

I can personally recommend the use of the satin sheet for both PLA and PETG. Good adhesion with both materials and the print self-releases as the sheet cools. I now use the smooth sheet only when I need to maximise adhesion for taller models that have just a small surface area in contact with the sheet. Again, this is what you learn by doing!

Cheers,

Tim

RE: Understanding Z offset when using different filaments

+1 for the satin sheet. One of the best things that has come out of Prusa.