Why are outer perimeters faster?

Bambu Lab Software Bambu Studio
1

It appears that very frequently outer perimiters are being printed faster than inner perimeters. I thought it was supposed to be the other way, so that the visible perimeters are “higher accuracy”. The example shown shows this effect, with the “greener” lines being faster than the yellow. This box is hollow, so there’s outer perimeters on both sides of the wall.

The issue exists both in Bambu Studio and OrcaSlicer. Does anyone know why this is so? Is this a bug?

Screenshot 2023-04-16 at 09.38.20
Screenshot 2023-04-16 at 09.38.201032×860 91.5 KB

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2

If you reach your filament max volumetric speed, then larger or thicker layers will print slower

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3

Understood, but that’s not’s what happening here. In this case, all layers are 0.20mm, and additionally I’m only comparing the perimeters on a single layer.

4

Could you post the same picture as you posted but one for the flow and one for the layers width please ?

EDIT :
because if speed settings are good inner speed>outer speed, I cant see any other explanations

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5

Actually, I think I figured it out. It’s line width that is the difference. The outer perimeters are thinner lines, which given consistent volumetric flow, means the outer perimeters can print faster.

So, inner speed > outer speed, given all other specs are equal, and they just happen to not be equal in this case.

The layer heights are identical for every layer, but the line widths, and volumetric flow, are different. Still want to see those pics ?

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6

nop that was my first thought, on your first picture inner perimeter looks larger than outer perimeters :wink:

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7

Thanks for the hint to check things related to volumetric flow. Appreciated.

8

You didn’t mention which print profile you are using.
There are differences in profiles that can change the speed of various parts of the print.

If you compare .2 standard to .2 speed you will notice that it slows down the outer perimeters quite a bit.

9

I had the same question and problem. It seems an odd situation when the outer Wall is printed faster (not slower) than the other inner walls. When I changed my model thickness to be a multiple of my line width it printed at the expected outer wall speed (slower).