Extrusion issues on medium speeds (while accelerating?)

Question

I've recently changed my Ender3's hotend to E3D v6 clone with Titan direct extruder, so I can print faster than on stock. But when I increased the speed up to 70 mm/s for walls and 80 mm/s for infill (PETG, nozzle temperature of 225 °C, bed temperature of 80 °C, 0.2 mm layer height, 0.4 mm layer width), I've faced this kind of issue:

Here's how it looks in Cura:

The printer's head goes from left to right, counter-clockwise and I get issues on both exits from curved shape.

First of all, I thought, it is connected somehow with retraction, but according to Cura, both problem places are in the middle of the current layer. Later I thought it could be related to Linear Advance and disabled it on the next test print, but it did nothing:( Slowing the printer down to 60-65 % in mid print solved the issue, but it's not what I changed the hotend for:)

Maybe someone has any ideas, what's wrong with it?

Answer 1

In my experience, 225 °C is the lower range for PETG, that combined with a higher than normal printing speed of 70 mm/s might be your issue. The lower your print temps the lower the maximum nozzle flow rate. I would recommend increasing the nozzle temperature.

For a point of reference, on my printer with an E3D v6 clone and a generic extruder I print PETG at 235 °C and 60 mm/s and 24 mm/s outer perimeter speed, with a 0.2 mm layer thickness. Though admittedly not optimized for speed.

Answer 2

In other words, your print exhibits issues when the hotend is accelerating, like if not enough filament were pushed in.

It is advised to calibrate for linear advance after replacing the extruder.

Check https://marlinfw.org/docs/features/lin_advance.html and

and check https://marlinfw.org/tools/lin_advance/k-factor.html

Answer 3

PETG can have difficulty printing at higher speeds.

See Why does PETG require slower speed?

Also, if the speed is too slow, it tends to have heat creep.

See What are ways to avoid heat creep?

Higher nozzle temperatures should allow faster print speeds, but will also increase the chance of heat creep and increase the slowest required speed to prevent heat creep.