PETG basic issue

I am having problems with only the underside of overhangs when printing PETG. I have dried the filament for 10.5 hours at 120 degrees Fahrenheit. I use Bambu presets for the filament setting. The picture below shows the bottom of the print. I removed numerous strings that crossed side to side to show the base of the print.

I am using a P1S with a textured PEI plate. There were no adhesion issues.

Sparse infill is cross hatch with 10% density

Speed is 200 mms for outer wall
300 mms for inner wall

I am probably providing too much information but I’m pretty new to this hobby and am unsure what information I need to provide.

Any help would be greatly appreciated.

Your speeds are too high for PETG. I don’t know why Bambulab hasn’t adjusted their default settings for PETG, but it is WAY too fast. Try these settings for PETG:

Bed: Engineering Plate w/ Liquid Glue
Bed Temp: 75°C
Nozzle: 0.4mm
Nozzle Temp (1st Layer): 255°C
Nozzle Temp: 260°C
Flow Ratio: 0.98
Part Cooling: 10% Min / 30% Max
Aux Fan Cooling: 40% (up to 60% depending on the overhang)
Exhaust Fan: 60-70%

Retraction: 1mm
Wipe While Retracting: YES

Then in the “Advanced” tab, under “Filament start G-Code” I added “G29.1 Z0.02” to raise the Z-Offset by a tiny bit so it keeps the nozzle away from the print, reducing clumps and stringing.

You can copy and paste this into you Filament Start G-Code and see if it helps:
; filament start gcode
{if (bed_temperature[current_extruder] >80)||(bed_temperature_initial_layer[current_extruder] >80)}M106 P3 S180
{elsif (bed_temperature[current_extruder] >60)||(bed_temperature_initial_layer[current_extruder] >60)}M106 P3 S180
G29.1 Z0.02

{if activate_air_filtration[current_extruder] && support_air_filtration}
M106 P3 S{during_print_exhaust_fan_speed_num[current_extruder]}

Slow down the print speeds. PETG can’t print that fast like Bambu default settings have it. Even on Bambu’s website for PETG, it even says <100mm/s for print speeds. They need to update their default settings for PETG badly. It just doesn’t work. So here are my speed settings that have worked for me:

Outer Wall: 40 mm/s
Inner Wall: 80 mm/s
Sparse infill: 110 mm/s
Internal Solid Infill: 80 mm/s
Top Surface: 60 mm/s
Bridge: 25 mm/s
Support: 100 mm/s
Support Interface: 90 mm/s

As far as the “Z-offset” being at 0.02, you can change it to where you like it. With some other PETG, I have gone as high as 0.04 and that has worked best, but you need to increase the flow ratio a tiny bit to get the print dimensions right, if that is important. Hence why I did the flow ratio at 0.98 instead of the 0.95 that is default.

For Supports, I use Tree (Auto) and “Organic” with 0.24mm Offset top and bottom with 2 interface layers top/bottom.

Anyway, hope this helps!

Thank you for taking the time to respond. I have learned a lot from reading the responses of more experienced users and really appreciate your assistance.

From just a single photo, it’s hard to conceptualize what the goal of the shape is intended to be. Two additional screengrabs would help. One of the model as it sits on the plate in the prepare screen and then another showing it in the preview screen after it has been sliced. From there, it will me much easier to understand what the printer is being asked to do.

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Sorry I’m new to this. I will keep in mind for future posts to send more pics. I was actually worried I was putting too much information into the post.
The response from tcqkvpwvps solved my issue. The prints are now coming out flawless since implementing the changed settings and g code addition. I do want to thank you for your feedback and willingness to assist a noob. It creators like you who are helping make this a fun hobby for me. I learn a lot from reading posts from the creators who make this a successful forum.

I made EVERY change you suggested and the prints are now amazing. I cannot thank you enough for taking your time to share your knowledge with a noob.