Default Line Width of 0.42

My first post on this forum and I’m going to ask a dumb question… While I’m waiting for my printer to arrive (P1S), I’m trying to get familiar with the slicer software. I’m new to Bambu but not new to 3D printing and have been using Cura for some time. I noticed that the default line width for walls and such is 0.42 instead of 0.4. I guess my question(s) is why 0.42 and not 0.4? And, does this have any effect on dimensional accuracy (both cavity dimensions and overall size?
Sorry if this has been asked about before, I did do some searches first but didn’t find anything.

I suspect you are referring to a 0.4mm nozzle.
A 0.40 width bead thru a 0.40mm nozzle would probable not produce a good layer bond.
A 0.42 width bead adds a little squish to bond the layers.

The concept has been used for some time and depends on your purpose. Besides the already mentioned better adhesion, there are other advantages of the plus 20%, such as stronger parts and a higher flow rate (crucial for high-speed prints);

Theoretically, the slicer will output a g-code accounting for the line width which in a well calinbrated printer will ensure dimensional accuracy. In practice, I am not having any issues with dimensional accuracy, and I mostly print functional parts with different filament materials.

The main issue, not so relevant for me is the influence on the print aesthetics - I can imagine that wall details are more noticeable with a thinner line; also, a beautiful surface depends on the infill, for which a higher line density is better which is achieved with thinner lines;

1 Like

Thanks! Makes perfect sense. I have to hold some pretty tight tolerances so it was a bit concerning.

“Squish” is achieved mostly through layer height. The reason a wider extrusion is used is because you can’t get an “exactly” 0.4mm width from the nozzle nor position it so exactly so that it won’t touch the neighboring layers.
Imagine having two parallel lines with a 0.4mm line missing between them. If you were to put the nozzle exactly between them, you’ll always end up with some miniscule overlap, this puts some slack in there and the “squished” filament is calculated so it fills the void, but it’s not the same squish used to bond the layers.
Another reason is that the material won’t always flow exactly down and it looks better when this inaccuracy is covered by the “squish” and not by an exact extrusion from the nozzle.

In practice, though, I don’t think it makes much difference nowadays whether you use 0.4mm, 0.42mm, 0.45mm or even larger width, in fact I get better quality (especially overhangs) with higher widths as the overlap is bigger, to an extent, but of course small details can be lost and rounded.

1 Like

It all certainly makes sense. It makes me wonder why Cura and others default to 0.4 line widths. To smooth out top surfaces, I’ve used line widths as small as 0.28 and they turn out great. I’m assuming the slicer (or firmware) compensates for the line width specified and lays the lines down accordingly. I might be comparing apples to oranges in comparing Cura to Bambu. I’ll know more wihen I finally get my hands on my P1S (waiting anxiously)…

If the slicer thinks the extrusion is 0.4mm wide, each parallel line will be centered 0.4mm from its neighbor. If the slicer thinks the extrusion is 0.42mm wide, each parallel line will be centered 0.42mm from its neighbor. The only way you get any “squish” is if the slicer thinks the extruder is 0.4mm but the extruder is actually 0.42mm. Then, you’ll get 0.42mm wide lines on 0.4mm centers, they’ll overlap. If you tell the slicer lines are 0.42mm when they’re actually 0.4mm, there will be a gap between adjacent lines.

0.42mm only makes sense to me if the extrusion width is really close to or the same as what the slicer thinks. I’m going to guess that it is purely a function of the nozzle, and for whatever reason, the BBL 0.4mm actually produces something closer to a 0.42mm wide extrusion.


I think the reason it does slightly overlap is that most steppers (at least the ones I’m familiar with in my current printers) have a step frequency of 0.05mm. So by specifying a line width of 0.42 should actually move the extruder by 0.4mm (rounding down) but actually extruding enough material for a 0.42 line width. It that’s true then it actually would overlap each line slightly. My guess is that Cura inherently over-extrudes slightly (when set to 100%) while BL is more precise and actually lets you set the amount of ‘overlap’. Just a guess.

Your first sentence you said layer height. Did you actually meant to say layer width?

I’m trying to chase down a “more squished” first layer as well, so trying to figure out what I need to tweak. Thanks!

1 Like

Yes, I really meant “height”.
There’s already enough squish, after all you are laying, say, only a 50% of the nozzle diameter. You need to increase it only if you want a more filled-in first or last layer, which is why it’s a tunable (I don’t think Bambu Studio has it, but OrcaSlicer does, so I think that’s what you should be looking for), but increasing “width” would also increase spacing and not really increase “squish” (not by much anyway). Maybe if we created a model we would (likely) find out that with higher width, more of the extrusion is touching the surface (be it previous layer or the bed), but it would be marginal, and you’d lose detail. I increase the first layer extrusion by a few percent just to avoid any potential gaps, but I don’t think it improves adhesion by much. You’d get more if you just slowed down or increased temperature for the first layer. After all - you’re likely not seeing gaps in the first layer, are you?

I thinkt it’d be a great idea to be able to overextrude the infill of the first layer without overextruding the first layer walls. It be nice to get a nice smooth bottom layer.

The standard wall thickness and other parameters in the slicer software may be set by default to some value, which may be slightly different from what is expected. In the case of Bambu, the default line thickness is set to 0.42 mm instead of the standard 0.4 mm used, for example, in Cura. This may be due to differences in algorithms and software settings. However, slight variation in line thickness usually does not greatly affect the dimensional accuracy of the printed parts, including cavity dimensions and overall dimensions.