Printing at 16 mm/s vs 20 mm/s causes overhang to fail

Bambu Lab H2 Series
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I printed a vase in vase mode that printed the most problematic overhang without a problem at 20 mm/s. The vase had this wavy mark line along it on one side horizontally that wasn’t deformed but it had a visible wave to it when light shined on it so I wondered if it would disappear if I printed it even slower. So I printed it at 16 mm/s without changing anything else and the overhang resulted in spaghetti. So I’m wondering how is it possible that printing it 4 mm/s higher prints without a problem and printing it slower fails. I’m using a 0.8 nozzle.

Here is the orcaslicer project of the overhang part:

01vasemode.3mf (229.8 KB)

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Gravity is a bitxh man it works over time

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It’s hard to see in the photo but these were what I meant by wavy marks:

IMG_2836
IMG_28361920×1824 669 KB

Now I guess the logical thing to try is to print it faster than 20 mm/s? Maybe because it is too slow the nozzle melts the already printed layer below. But why does it only happen around the same angle?

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Seems like VFA’s.

Those get usually worse at lower feed rates.

So yes, higher feeds might help reduce this.

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