empty spaces at the bottom

[Corrado1 0]

I'm sorry for my english.
The lower surface appears much more damaged on the printed object than the upper surface.
Initially I thought it was a problem caused by the supports (and it probably is).
However, observing the construction layer by layer, I noticed that layer number 23 was "missing" some yellow lines.
I do not know what to think.
I'm a beginner but I really want to learn how to print better.
My printer is an elegoo neptune 3max.
Thanks for your help

EN3MAX_bracctto.3mf

[Slashee_the_Cow 269]

It's "missing" those lines because the area narrows and it can't gracefully reduce the the number of lines to match it (and it will absolutely refuse to give up the extra skin wall). Here's what it looks like if I change Top/Bottom > Extra Skin Wall Count to 0:

Not really a perfect solution because the extra skin wall is usually a good thing, but there's a lot worse ways to muck up a print than removing your skin wall, so don't feel too bad if this is the route you want to go.

 

Of course you're forcing it to do lines in that single direction, if you set it to lines without overriding the angle it fills the area fine:

But I get the feeling you want the lines to be going along the length of the object for looks. Warning though: at 90° exclusively it's not great for strength because it's not adding any strength on the Y axis or to resist shear or twisting.

 

So can I suggest a compromise? Here's the Concentric pattern:

It fills the area gracefully because instead of just stopping walls where it needs to get thinner, it just makes them follow the outer contours.

[Corrado1 0]

I AM SPEECHLESS!
Truly super helpful and very competent!!

since you are currently the only one to answer my problems I'll ask you the next question: starting from the printing profile you suggested for PLA, what changes would you make to print PETG?
From what I understand the salient points are the retraction and the power of the fan.
Consider that I am looking for solid objects... I can improve the aesthetics in post production with a little sandpaper and painting.
Thank you in advance

[GregValiant 1,255]

The retraction distance should be near the max for the printer.

The bed needs to be hot.  I print a lot of PETG and the bed is at 83.  I use hairspray as an adhesion promoter on 100% of my PETG prints.  Long thin parts will still want to warp and pull off the bed.  There are plugins in the Marketplace for "Tab anti-warping".  You size the meshes and slide them around in Curs to provide additional footprint to the model.

The "elephant ear" on this is 2mm thick and it almost wasn't enough.  It managed to pull up by about a millimeter prior to the print finishing.

 

A lot of people will tell you not to use the fan with PETG but I find that some fan helps a lot for things like the first layer over support and the first skin over infill.  You can go into the gcode and add fan lines at appropriate layers, or you can use multiple instances of Search and Replace to turn the fan up at one layer and turn it off again at the next.

large horizontal holes also need some fan as the feather edges start to close at the top.  They will want to warp upward and the nozzle can hit them.  Z-hops for that situation is a good idea.

[Slashee_the_Cow 269]

I don't seem to have the same trouble @GregValiant does with PETG. I've never needed to use additional adhesion, though it could be a build plate thing - I have whatever powder coated (I think) metal thing that comes stock with the Ender-3 V3 SE and I think he has a glass plate, I've never needed to do anything to the bed, only need to add adhesion in Cura for very thin parts or things with a very small base of support and never had trouble with warping. It does need to run quite hot (I run my bed at 80, but I'm not sure if it actually gets any higher).

 

I will also respectfully disagree about the "maximum retraction" part of it, although it could be different if you use a Bowden extruder. PETG is stringy so does need more retraction, but for example, with my direct drive extruder, I retract PLA 0.8mm, PETG 2mm and TPU 3mm. You don't want to over-retract if you can avoid it (the gears in the extruder can grind up the filament a bit and you might not have the nozzle pressure required for filament to start flowing immediately) but it's really a case of trial and error to find out what works best for you (remember: small scale testing is your friend, don't print a big thing five different times).