First Layer Extrusion Width
I was having some issues with gaps between infill and perimeters at the first layer. On this note I was checking the first layer Sli3er settings. I noticed that the extrusion width is lower at the first layer. (e.g. 0.1mm profile: 0.42 and 0.45 for other layers).
My understanding was, that a nice first layer would be easier with a higher extrusion width. Slic3r even suggests a value of 200%. Does anyone has any insight why the setting was chosen this way?
3 years later, i still have the same question 😊
Slicer recommend a combination of high first layer and 200% extrusion width.
First layer height.
A thicker layer height will provide more flow, and consequently more heat, making the extrusion adhere to the bed more. It also gives the benefit of giving more tolerance for the levelness of the bed. It is recommended to raise the first layer height to match the diameter of the nozzle, e.g. a first layer height of 0.35mm for a 0.35mm nozzle. Note: The first layer height is set this way automatically in simple mode.
Fatter extrusion width.
The more material touching the bed, the better the object will adhere to it, and this can be achieved by increasing the extrusion width of the first layer, either by a percentage or a fixed amount. Any spaces between the extrusions are adjusted accordingly.
A value of approximately 200% is usually recommended, but note that the value is calculated from the layer height and so the value should only be set if the layer height is the highest possible. For example, if the layer height is 0.1mm, and the extrusion width is set to 200%, then the actual extruded width will only be 0.2mm, which is smaller than the nozzle. This would cause poor flow and lead to a failed print. It is therefore highly recommended to combine the high first layer height technique recommended above with this one. Setting the first layer height to 0.35mm and the first extrusion width to 200% would result in a nice fat extrusion 0.65mm wide.
The values in Prusa Slicers defaults are in there as thats what countless hours of printing on the prusa farm have been shown to work. With a properly clean bed and suitably set Z height you should get great first layers and awesome adhesion (at least with a smooth sheet). I think its because when you have that perfect height and squish then anything extra can lead to over extrusion on that first layer.
The great thing about it though its if you want you can change it. Experiment, set different values and see what works for YOU. The defaults are what Prusa determines works for MOST.