December 6, 2025
Description
NOTICE: There is a bug in the latest BambuStudio that appears to reset the value you enter in step 5 (plate 7). The value is stored, it is only the number that you see that resets so it still works. Sometimes however, Bambu Studio may crash when changing these surface flow values in the object tab. If it does, print only one model at a time and change the global value instead.
In collaboration with MakeWonderfulThings: https://makerworld.com/en/@MakeWonderful thank you for your feedback and support!
Welcome!
This model and guide is designed to showcase many common issues or imperfections that can be seen on the top surface of a print.
Instead of a simple small square or circle, it will show issues that can appear in a wide variety of models and situations.
The goal is for you to learn what causes an issue and how to fix it as well as providing a platform for you to test settings on your own for an even smoother surface.
Boost MeIf you learn something useful from this, feel free to send a boost!
[Work in progress]
Purpose
My original purpose with this was to find a more consistent alternative to ironing (people need vastly different settings) but I decided to also document various surface issues and how to fix them. If the top layer doesn't look good with standard settings, we should take a step back and fix any underlying issues first.
Depending on the reason you are using ironing, it may not be needed at all after following this guide.
How to improve the top surface
My preferred method is to reduce the top surface line width. (Enable advanced settings to change this). This will also reduce the size and visibility of imperfections and lead to an overall better surface.
Smaller lines are smoother but may create their own issues (refer to pictures) so I recommend using lines wider than 0.25mm.
75% of the nozzle diameter is a good starting value (0.3mm for a 0.4mm nozzle).
Something like 0.35mm can likely be used as a default with no further tinkering. But please experiment on your own and let me know in the comments what settings worked best for you and what printer and filament you used!
Top Surface line width:
Top surface speed:
Top surface flow:
Filament:
Printer:
(Future work: Ironing)
A smoother top surface will also give ironing a better foundation to work on. Hopefully this can lead to being able to iron with more similar settings across different printers, filaments and people. To test this theory I need your help so please share your findings and settings used for this too.
[insert picture of ironing on standard settings surface vs smaller line width]
Getting started
Open the project and follow the instructions. Remember to print one with standard settings first to make sure there are no underlying issues!
Refer to the pictures for explanations and guidance.
If you miss any instructions, let me know. Make sure to add this project to your collection so you can find it again.
Model features, see pictures. (For in depth descriptions, see the bottom of this document.)
The following top surface issues can be seen on the model:
The model prints in about 10 minutes (not counting printer startup)
The thickness ensures there is sparse infill which prevents bed related issues from affecting the top layers. We can also experiment with infill settings and number of top layers if needed. My recommendation is to use at least 6 top layers for 0.20mm layer height.
What the model doesn't show:
Settings of importance
Prerequisites
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In-depth descriptions if you want to know more. Completely optional! [Work in progress]
There are numerous factors that affects the top surface finish. If you want to know more than what is included in the pictures, here are more detailed explanations. This is all based on my own experience and extensive testing over years of working with 3D-printing. That said, I don't know everything and I welcome any input if you have other experiences or knowledge. Especially if you disagree with me.
Transition lines:
A printed line will always become slightly wider than the line width setting. In reality, the sides of a printed line are rounded and will bulge out on the middle. When the next line is printed next to it, it will be pushed ever so slightly to the side. This usually has no practical importance but when a new line is printed between two already printed lines there will be less space for it. It will look different and can be felt as raised edge, especially if flow isn't calibrated. This effect is greatly reduced by using a monotonic top surface pattern which is typically enabled by default. Transition lines on the solid infill layer below the top surface can often be seen through the top surface unless that layer too has a monotonic pattern. They will appear perpendicular to the top surface transition lines.
However there can still be a small visual difference even with monotonic when the printer returns to continue an already printed area.
Suggested solutions:
There is a third type of line that can be seen primarily on transparent filaments and shiny filaments.
When printing top and bottom layers that is not visible on the outside of the print, the slicer ignores retractions which may leave drag marks and oozing on those layers. They can sometimes be visible through the top surface.
Suggested solution:
Surface variations:
Small and large top surface areas often looks different. This can have different causes but the biggest one is probably speed and acceleration related. When the printer starts printing a line, it will take some time before it reaches it's top speed. This delay is determined by the printers acceleration. Slow speed at the start and end of lines often makes the surface more shiny while larger, faster areas can become more matte. Therefore, a lower top surface speed can reduce the visual difference. Different filaments behave differently though. Flow and Flow dynamics can have a large impact too.
Suggested solutions:
Ironing
During ironing the filament is extruded very slowly and will spend a longer time in the hotend. This can degrade the filament to the point where an ironed surface starts out looking good but turns bad after a while depending on the settings. The larger the area, the higher the risk for it to happen. It will take a while for all the degraded filament to exit the nozzle after the ironed surface is finished so the next area of the print may also start out worse.
You can reduce this risk by increasing how fast the filament is extruded during ironing. (I do not recommend changing Ironing flow for this specific purpose).
Suggested solutions:
Gaps near walls at the end of lines (not seen in the slicer):
Sometimes when a top surface line meets a wall it will not connect at the end, leaving gaps. This can be caused by not having calibrated flow (too low) or flow dynamics (too high K-value) and is more or less common with different filaments.
For the “Monotonic” pattern, you can increase “Infill/Wall overlap” but this may have side effects in other areas since we are essentially adding more material everywhere infill meets a wall.
For the “Monotonic lines” pattern, you can try increasing “Monotonic line travel extend". It doesn't overlap the lines but it can help connect the line ends better.
Suggested solutions:
Increase temp
Gapfill:
Some areas of a print cannot be filled with an ordinary line because it's too big. The slicer will use gapfill settings instead. These gaps are largest where top lines run almost parallel to a wall.
The amount and size of gaps that needs to be filled will vary with the model geometry and some settings. Wider lines will lead to fewer but larger gaps that needs to filled.
Over- and under-extrusion:
We want lines to print without any signs of gaps between them while not extruding more filament than there is room for. In my opinion, Bambu Studio's built in manual flow calibration is not very accurate and I recommend finding an alternative on Makerworld with good ratings.
Over-extrusion will be visible as blobs, ridges and a rough top surface and can make filament build up on the nozzle. It can reduce dimensional accuracy. A small amount of over-extrusion can make the print stronger and improve transparency of clear filaments. It can also make vases watertight.
Under-extrusion will be visible as gaps between lines and the print will be easier to break. A small amount of under-extrusion can improve dimensional accuracy and prevent filament buildup on the nozzle for sticky materials like PETG.
In a perfect world, the cross-section of a printed line would be a rectangle and there would be no gaps between the lines at all. In real life, lines have rounded sides so it will be impossible to completely fill in all space between them. There will be tiny gaps where the corners would be (it's one of the reasons transparent filaments aren't clear when printed). In this example, extruding the theoretical 100% flow would mean more filament than there is room for. However, this is not the entire story.
Different materials behave differently when extruded (die swell, viscosity, moisture content etc.). For these reasons, the default flow varies for different filaments.
Filament tolerances also directly affects the final result.
Flow dynamics calibration issues:
When the extruder starts or stops, there is a tiny delay before the flow changes at the nozzle tip. Without flow dynamics (also called pressure advance), this would lead to too much filament being extruded when the printer slows down and too little when it accelerates. With calibrated flow dynamics, the extruder starts and stops a small distance before a speed change to compensate for this. Typically, the more flexible a filament is, the more compensation is needed.
Too much compensation (the K-value) will lead to gaps near walls and rounded corners.
Too little compensation will lead to overextrusion near walls and underextrusion in the middle of flat surfaces. The corners will swell.
There is also a setting in Orcaslicer: “Small area flow compensation”. This aims to improve pressure advance for short lines where it typically isn't as accurate: https://github.com/OrcaSlicer/OrcaSlicer/wiki/quality_settings_wall_and_surfaces#small-area-flow-compensation
Delamination of the top surface layer:
This can happen with too small line width in relation to the nozzle diameter. The main causes (as I understand it) is:
The contact area is very small, giving low layer adhesion.
The filament is not being squished into the surface below also giving low layer adhesion.
The flat surface of the nozzle will “rub” on already printed lines, pulling and dragging them loose.
Possible solutions:
Warping
If a model starts getting loose from the buildplate it can warp, pushing previously printed layers upwards. When the next layer prints, there wont be enough room for it, causing local over-extrusion. Sometimes a model only loosens a little bit at a corner or along an edge and it may not be obvious at first glance. On thin parts, this can affect the top surface.
Difficult overhangs
Steep overhangs or overhangs that aren't cooling fast enough tend to rise up, giving less room for the next layer. Lower layer height helps but too low and the layer doesn't have enough rigidity to keep its shape while cooling. Wider lines help too. But this is another topic.
License:
MakerWorld Exclusive License
Criticalprint3d
