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PETG: what am I missing?  

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jwr
 jwr
(@jwr)
Eminent Member
PETG: what am I missing?

I got my new i3 a couple of weeks ago and have been very impressed with PLA prints. Everything I printed was basically flawless, the results exceeded expectations.

So, I tried printing in PETG Orange (Prusament). I put the powder-coated sheet on, loaded the filament, used PrusaSlicer with PET settings and got this:

I aborted the print, as it was clearly going nowhere useful. A couple of days later I realized I hadn't cleaned the sheet before printing. It was factory new, but still. So I meticulously cleaned the sheet using lots of isopropyl alcohol, tried another print, and got this:

The lines seem too thin and some do not stick to the bed.

There must be something I'm missing — given the absolutely perfect results I'm getting with PLA, I expected PETG to be similarly easy out of the box. I am using all default settings, the only difference is that the slicer is set to PET instead of PLA. Any hints?

 

Posted : 21/12/2021 8:11 am
adesir
(@adesir)
Reputable Member
RE: PETG: what am I missing?

Welcome on board!

The textured sheet is thinner than the smooth sheet used for PLA. So you have to calibrate again you first layer. The printer can manage several sheets with first layer settings: https://help.prusa3d.com/en/article/steel-sheet-profiles_1955

 

Posted : 21/12/2021 8:30 am
Titan
(@titan-2)
Estimable Member
RE: PETG: what am I missing?

As adesir says, it looks like you have switched from smooth to textured print sheet and so will need to calibrate the layer height again as the sheets are different thicknesses. But, even if you're using the same print sheet, PLA and PETG require the nozzle to be a different distance from the bed. PETG should be slightly further from the bed compared to PLA , but not as far as in your photo. Try adjusting the Z height closer until the PETG is being laid down (not quite as squished as PLA) but also low enough that the filament still overlaps adequately forming a solid area.

Posted : 21/12/2021 9:00 am
jwr
 jwr
(@jwr)
Eminent Member
Topic starter answered:
RE: PETG: what am I missing?

Ok, that makes sense — I will try the first layer calibration and report the results!

But I'm confused: reading the manual, I got the impression that first layer calibration is required for the kit only (I bought the pre-calibrated printer) and my understanding was that the SuperPINDA probe is supposed to measure the distance between the nozzle and the print bed, before every print.

Doesn't the SuperPINDA probe do exactly that?

 

Posted : 21/12/2021 9:12 am
Titan
(@titan-2)
Estimable Member
RE: PETG: what am I missing?

The Pinda probe simply measures the distance from the bed, you still have to calibrate the nozzle height for each print sheet and for each type of filament.

Posted : 21/12/2021 9:24 am
adesir
(@adesir)
Reputable Member
RE: PETG: what am I missing?

And there is a possible simplification: if you print PLA on the smooth sheet and PETG on the textured sheet, you just switch between two sheet profiles with no further calibration.

The printer calibration and first layer calibration are not the same thing. The first is done by Prusa if you bought the assembled printer. The first layer is still to be done when you change the sheet, or the noozle. Just follow carefully the manual. 

Posted : 21/12/2021 9:59 am
jwr
 jwr
(@jwr)
Eminent Member
Topic starter answered:
RE: PETG: what am I missing?

Ok, I think I understand — so the PINDA probe measures the distance from the bed, not the top of the sheet? I think that's what I was missing.

Anyway — after several calibration tries I think I found the right value (slightly squished lines), which turned out to be -1.14 in my case. And it seems that this worked well and my first PETG print is proceeding quite nicely.

Thank you for all the help!

Posted : 21/12/2021 11:32 am
fuchsr
(@fuchsr)
Noble Member
RE: PETG: what am I missing?

And remember you can use steel sheet profiles (under Settings/HW setup in the printer's menu) to store Live Z values for different sheets.

Posted : 21/12/2021 12:27 pm
Neophyl
(@neophyl)
Famed Member
RE: PETG: what am I missing?

Not quite.  The pinda probe does measure the distance to the steel print sheet, not the bed.  Its inductive so it picks up metal.  The bit you are missing is the coating on the sheets varies.  The smooth PEI sticker is thicker than the powder coated textured sheet coating.  Also different sheets of the same type also do vary too.  Aaaaaaannnnd one SIDE of a powder coated sheet might need a slightly different tweak if the sides werent sprayed to the same level.  Remember we are talking microns of distance here.  The z offset values allow you to take this variance into account.

Its why the printers firmware allows you to store several z offsets, so you can match them up with each individual sheet.

Posted : 21/12/2021 1:05 pm
Artur5 and jwr liked
jwr
 jwr
(@jwr)
Eminent Member
Topic starter answered:
RE: PETG: what am I missing?

Thanks for all the explanations, it makes perfect sense now! And I'm getting very good results (though I did tweak the Z height some more, it seems the best way to do this is to print a filled square, not use the Prusa-supplied calibration routine).

Posted : 29/12/2021 12:03 pm
Armand
(@armand)
Active Member
RE: PETG: what am I missing?

Hi 

 I find that the difference between the smooth and textured 2 sheets are 0.3 thus as a rule of thumb I always lower my Z by 0.3 from what my smooth sheet setting is for the Textured sheets works every time , well for me at least 

Posted : 30/12/2021 9:52 pm
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