Traditional slicers have speed settings for specific extrusion lines, for example, inner wall speed, outer wall speed, infill speed, solid infill speed, etc. The outer wall and inner wall speed have a great influence on the surface quality of the printed model, especially for overhang surfaces.
Generally speaking, overhang surfaces have no problem when the whole printing speed is slow. But for high-speed printing scenarios, too fast wall speed will make overhang quality very bad, even though the layer area is large so that layer printing time is long and layer cooling is enough.
In order to make the overhang surface better, we usually use lower wall speed for models which have an obvious overhang. However, different model parts have different overhang degrees, even at the same layer height. In order to make the balance between printing time consumption and printing quality, it's necessary to detect the overhang area and just make these areas printed slowly. So we introduce a setting group “Slow down for overhangs” to control wall speed for different overhang parts in Bambu Studio.
When enabling "Slow down for overhangs", extrusion lines of the wall will be divided into several groups according to different overhang degrees. And lines with different overhang degrees will be mapped to different printing speeds.
Overhang degree is expressed as a percentage from a microscopic point of view that the width of the filament is not supported by the lower layer. The figure is shown below.
Calculating the overhang degree for every extrusion line of the wall needs some 2D graphical arithmetic operation and costs a lot of time. So we sample and make the overhang degree to be just a four-part form to avoid slicing being very slow. Overhang degree 0% means no overhang. And 100% means bridge. So please note that 0% is not included in (0%, 25%) part, and 100% is not included in [75%, 100%) as well.
If you don't want this feature, you can just unselect the setting "Slow down for overhangs" and the overhang speed will also be hidden and doesn't work.
Print two copies of one model at the same time and disable "Slow down for overhangs" for the right object. Different printing speeds of overhang can be seen on the speed preview page.
(Thanks for the designers of this test model and it can be downloaded here: https://github.com/kickstarter/kickstarter-autodesk-3d)
The overhang quality comparison is shown below. The left pictures are the overhang surface of the model which enables "Slow down for overhangs". And the right pictures are the overhang surface of the model which disables "Slow down for overhangs".
We can see that the quality of the left model is much better than the right.