Poor Print Quality on Sloped Surfaces That Face the Rear - General discussion, announcements and releases

RE: Poor Print Quality on Sloped Surfaces That Face the Rear

t5montecarlo — Wed, 21 Jan 2026 14:54:40 +0000

I chose to remain with Prusa and not get Bambu due to the support concerns I have read about over the last year, though I understand the Bambu prints very well. My set up for the last 5 years is an MK3S kit, then MK4S kit, in a Lack table enclosure (with added LED ribbon lighting) and it isn't as good as it could be since the design and profiles are intended for open environment. I have also read about teething issues Prusa has had with the Core One, but I also feel it is their current baby and it will get attention, and that the i3 series will fade away. The XL, Core One L, and so on are outside of my price range and needs. Yes, an enclosed printing chamber was my goal since my MK3S to avoid the temperature swings/drafts from the forced air heating/cooling system in the house.

RE: Poor Print Quality on Sloped Surfaces That Face the Rear

jan.d.slay — Wed, 21 Jan 2026 14:35:17 +0000

What are you not telling me?

That was a purely humorous reference to all the bugs that Core One has had since it came on the market.

I thought long and hard about whether I needed a second printer. The Bambu Lab X1C was too tame for me. If everything works and nothing breaks, it's boring... or so I thought.So the Prusa XL got a Core One. But I already knew what flaws I might encounter and what teething problems the Core One might have.What was your decision? A closed printing chamber?

RE: Poor Print Quality on Sloped Surfaces That Face the Rear

t5montecarlo — Wed, 21 Jan 2026 13:38:20 +0000

What are you not telling me?

RE: Poor Print Quality on Sloped Surfaces That Face the Rear

jan.d.slay — Wed, 21 Jan 2026 11:49:40 +0000

I have a kit on order to convert my MK4S into a Core One+.

Wow! Not bad.... 😎

Have you thought this through carefully? 🤣 😉

RE: Poor Print Quality on Sloped Surfaces That Face the Rear

t5montecarlo — Tue, 20 Jan 2026 22:34:29 +0000

That's good news. For my particular print on the narrow edge, the textured plate is creating a bulging first couple of layers, complicating the post processing. I have read that the Bambu print sheet is the same dimension as the Prusa.

I am going to change the chamfer from 1 mm to 2 mm and see what it looks like. If the appearance is OK, I will try that after I get a satin print sheet.

I have a kit on order to convert my MK4S into a Core One+.

RE:

jan.d.slay — Tue, 20 Jan 2026 12:20:25 +0000

Jan, are you using the Satin sheet? Does it work as well with PETG as the textured sheet?

I initially ordered the satin-finished printing plate for the Core One. Currently, I am using the PEI from Prusa or the textured one from Bambu Lab X1C. I still had some left over, and it fits the Core in terms of dimensions.

However, I am using the satin-finished printing plate on the XL if i printing PETG, and it is simply brilliant.

RE: Poor Print Quality on Sloped Surfaces That Face the Rear

t5montecarlo — Mon, 19 Jan 2026 22:27:29 +0000

Jan, are you using the Satin sheet? Does it work as well with PETG as the textured sheet?

RE: Poor Print Quality on Sloped Surfaces That Face the Rear

jan.d.slay — Fri, 16 Jan 2026 09:08:45 +0000

Good Morning.

I am very pleased to receive such a comprehensive and detailed response. I have taken the time to answer your questions as best I can.

hank you for your project file. I have tabulated the differences between your project file and mine. Many may not apply to the MK4S due to different speed/acceleration capabilities.
You have something different from the default in the Start G-Code, but I don't know how it differs from the default. It also may not apply to the MK4S.
It is unfortunate that we aren't using the same base Print Settings; I used 0.15 mm Structural and you used 0.015 mm Balanced, which isn't available on the MK4S. As a result, some of the default parameter settings aren't going to be comparable.

The modified GCode is just a faster version to get the printer ready to start. I am currently testing it extensively to see if it has a negative impact on quality or layer adhesion.

How did you decide to change the Extrusion Multiplier to 1.055 from 1.000?

I determined this factor because I am not using original Prusa filament. I am using a 2 kg roll of black PETG from the German manufacturer “Material4Print.” At 1.000, I had under-extrusion, and with this increase of 0.055, I had smooth surfaces again.

Why did you reduce the first layer and all other layer bed temperatures?

Here, too, this change is due to the non-original filament. With PETG from Material4Print, you get nicer and more stable layers if you work below the upper limit of the specified printing temperature.

Your fan speeds are higher than the default and higher than mine. How did you decide to change them?
I already increased the fan speed and the result was worse.
Why did you reduce the number of layers where the fan was disabled?

With this filament, I have found that the default settings in PrusaSlicer (regardless of brand) cause layers that receive no or reduced fan speeds to become more shiny. The layers above them look more matte. This change is based on my experience with this filament in order to achieve a kind of uniformity. I don't have any adhesion problems due to the earlier onset of cooling (with small components).

Why did you increase the Max volumetric speed?

This is also a measured value that I determined through testing. Normally, it could be even higher because I printed more slowly, but this value is optimal for my PETG for now.

Why did you reduce the First layer height?

This is a standard setting that I use. It has a bonding base on the printing plate. With this setting, I can work well with all printing plates. 0.20 mm is too much for me.

Do you always use 6 perimeters? or did you just want to change this model from 5 to 6 perimeters?

At this point, I wanted to test whether it makes a difference to increase the perimeter or use 100% infill. It always depends on the printed part how you want to proceed. This setting was purely experimental.

Did you purposely not enable Extra perimeters if needed and Avoid crossing curled overhangs?

Yes.This setting was purely experimental.

Why did you enable Single perimeter on the top surfaces?
Why did you enable Only one perimeter on the first layer?

I chose this setting to achieve a more attractive appearance and to allow the infill to be distributed evenly across all layers. This is again based on experience. For small print objects, I only print a perimeter and fill the rest with infill. In my opinion, this is better than printing 3 or 4 lines in the first layer and then filling the rest with a few lines. It just looks nicer when the top and bottom are the same.

The Speed settings were greatly reduced from the default. Does the Core One typically print poorly at the default speeds?
My Perimeter, Small Perimeter, and External Perimeter speeds are already slower than yours.
My Perimeter and and External Perimeter acceleration settings are already lower than yours.

Before writing this post, I had already made a few prints with the black PETG from Material4Print. The settings from this company are only available on the website for the MK4. Unfortunately, the default settings are not good. That's why I had to start finding my own optimal print settings and filament settings for the XL and C1. I have to say that your project has helped me improve my PETG settings even further. Here too, as you might expect, reducing the speed and acceleration is something I learned from experience with PPA-CF. I have now applied this knowledge to PETG. Basically, you should always keep in mind that we are heating plastics and dynamically pressing them out of a narrowed nozzle with slight overpressure. Added to this are the mass of the extruder and acceleration and deceleration due to the belt drives. The fact is, the slower everything goes, the higher the chance of obtaining good quality results. I prefer quality, and quantity is rather secondary.

You initially said you thought the poor quality at the lower layers was not due to cooling, but speed and acceleration. From the project comparison, my speed and acceleration are already lower than yours. From the settings comparison, do you have a different opinion? It is difficult comparing different machines, so I don't know if a conclusion can be had from the data.

I suspect this has something to do with the filament. But that's just a guess. I have set the speed and acceleration to be almost the same in all areas for another print test. I am still testing the settings myself to achieve the best appearance and optimal layer adhesion.

RE:

t5montecarlo — Thu, 15 Jan 2026 22:27:26 +0000

Thank you for your project file. I have tabulated the differences between your project file and mine. Many may not apply to the MK4S due to different speed/acceleration capabilities.

You have something different from the default in the Start G-Code, but I don't know how it differs from the default. It also may not apply to the MK4S.

It is unfortunate that we aren't using the same base Print Settings; I used 0.15 mm Structural and you used 0.015 mm Balanced, which isn't available on the MK4S. As a result, some of the default parameter settings aren't going to be comparable.

Setting	Core One Default (0.15 mm Balanced)	Core One Setting	MK4S Default (0.15 mm Structural)	MK4S Setting
Extrusion Multiplier	1.000	1.055	1.000	1.000
First layer and Other layer nozzle temps	250 °C/250 °C	255 °C/255 °C	255 °C/255 °C	255 °C/255 °C
First layer and Other layer bed temps	85 °C/85 °C	80 °C/80 °C	85 °C/90 °C	85 °C/90 °C
Cooling slowdown logic	Consistent Surface	Uniform Cooling	Consistent Surface	Uniform Cooling
Fan speed Min	30%	50%	20%	35%
Fan speed Max	60%	70%	40%	40%
Bridges fan speed	60%	75%	40%	40%
Disable fan for the first	3	2	3	3
Full fan speed at layer	5	3	5	5
Dynamic fan speed for 0% overlap (bridge)	60%	75%	40%	40%
Max volumetric speed	12 mm³/sec	13 mm³/sec	24 mm³/sec	24 mm³/sec
First layer height	0.2 mm	0.15 mm	0.15 mm	0.15 mm
Perimeters	5	6	2	5
Solid layers top	6	4	6	6
Extra perimeters if needed	Disabled	Disabled	Disabled	Enabled
Avoid crossing curled overhangs	Disabled	Disabled	Disabled	Enabled
Seam gap distance	15%	15%	15%	1%
Single perimeter on the top surfaces	Disabled	All top surfaces	Disabled	Disabled
Only one perimeter on the first layer	Disabled	Enabled	Disabled	Disabled
Fill density	15%	30%	15%	15%
Fill pattern	Grid	Cubic	Grid	Grid
Brim width	0 mm	3 mm	0 mm	5 mm
Auto Generated Supports	Disabled	Enabled	Disabled	Disabled
Style	Snug	Organic	Snug	Organic
Support top contact Z distance	0.17	0.15	0.17	0.2 (detachable)
Support top interface layers changed from 3 (heavy) to 1 (light)	3 (heavy)	1 (light)	3 (heavy)	3 (heavy)
Support on build plate only changed from Disabled to Enabled	Disabled	Enabled	Disabled	Disabled
Speed Perimeters	150 mm/s	50 mm/s	80 mm/s	50 mm/s
Speed Small perimeters	170 mm/s	40 mm/s	45 mm/s	50% (25 mm/s)
Speed External perimeters	170 mm/s	50 mm/s	45 mm/s	50% (25 mm/s)
Speed Infill	150 mm/s	50 mm/s	110 mm/s	110 mm/s
Speed Solid Infill	150 mm/s	50 mm/s	140 mm/s	140 mm/s
Speed Top solid infill	100 mm/s	50 mm/s	80 mm/s	80 mm/s
Speed Support material	120 mm/s	50 mm/s	120 mm/s	120 mm/s
Speed Gap fill	120 mm/s	50 mm/s	60 mm/s	60 mm/s
Modifiers First layer speed	45 mm/s	50 mm/s	40 mm/s	40 mm/s
Modifiers First layer solid infill speed	100 mm/s	50 mm/s	100 mm/s	100 mm/s
Acceleration External perimeters	2500 mm/s²	1500 mm/s²	1500 mm/s²	1500 mm/s²
Acceleration Perimeters	3000 mm/s²	1500 mm/s²	2500 mm/s²	2500 mm/s²
Acceleration Top solid infill	2000 mm/s²	1500 mm/s²	1200 mm/s²	1200 mm/s²
Acceleration Solid infill	6000 mm/s²	1500 mm/s²	3000 mm/s²	3000 mm/s²
Acceleration Infill	5000 mm/s²	1500 mm/s²	4000 mm/s²	4000 mm/s²
Acceleration Default	3000 mm/s²	1500 mm/s²	2500 mm/s²	2500 mm/s²
Infill perimeters overlap	15%	35%	15%	15%

I have questions as to why you chose some of the values before I try them on my MK4S.

How did you decide to change the Extrusion Multiplier to 1.055 from 1.000?
Why did you reduce the first layer and all other layer bed temperatures?
Your fan speeds are higher than the default and higher than mine. How did you decide to change them?
I already increased the fan speed and the result was worse.
Why did you reduce the number of layers where the fan was disabled?
Why did you increase the Max volumetric speed?
Why did you reduce the First layer height?
Do you always use 6 perimeters? or did you just want to change this model from 5 to 6 perimeters?
Did you purposely not enable Extra perimeters if needed and Avoid crossing curled overhangs?
Why did you enable Single perimeter on the top surfaces?
Why did you enable Only one perimeter on the first layer?
The Speed settings were greatly reduced from the default. Does the Core One typically print poorly at the default speeds?
My Perimeter, Small Perimeter, and External Perimeter speeds are already slower than yours.
My Perimeter and and External Perimeter acceleration settings are already lower than yours.

You initially said you thought the poor quality at the lower layers was not due to cooling, but speed and acceleration. From the project comparison, my speed and acceleration are already lower than yours. From the settings comparison, do you have a different opinion? It is difficult comparing different machines, so I don't know if a conclusion can be had from the data.

RE:

jan.d.slay — Thu, 15 Jan 2026 18:58:21 +0000

Thank you. You only had to print the model stub, not the full model, but I greatly appreciate your help.

I'd be delighted to. As I mentioned, I'm always happy to assist, especially when it comes to my own hobby.

You have proven that that the Prusa XL can print the model. One difference between the XL and MK4S is that the XL cooling fan duct is rotated 180 degrees from the MK4S duct. The edge in your print that is opposite my problematic edge looks OK.

Then I'm happy to tell you that I printed it with my Prusa Core One. I could have printed it with the Prusa XL, but I think the Core One is closer to the MK4S :-)

I have already slowed down the printing process by 37.5% and the problem still exists. Your print speed is much faster, so I assume it is per the profile default. At times, I wish I had bought the Core One kit instead of the MK4S kit.

That's correct. I have now discovered that I can print my PETG very nicely if I increase the cooling and set it evenly, and reduce the speed and acceleration.

Here is the project file I promised.

Test_Print.3MF

I am still open to setting change ideas to make the model or model stub print properly on the MK4S. The problem was solved on my MK3S with an improved cooling fan duct. Modifying cooling and speed made the model print in PLA on my MK4S. I still believe the PETG print needs additional cooling help; some setting changes have improved the problem area while other changes have made the problem worse. I still need to see how it prints outside the enclosure, which will help to point to a cooling issue. I may make time to try that today and report back.

Then I would say, test the settings on your MK4S and then we'll talk again.

Bye Jan