Hi everyone,
I have little problem with underextrusion when my printer starting new layer. When starts new layer - internal perimeter first, there is discontinuous line (very often a few layers in a row). After a few milimeters line is filled up and everything is ok. What can cause this kind of problems? I’m looking solution in retraction. I use bowden MK8 ekstruder and E3D v5 clone with teflon tube. Printing with PETG in 235C (220-250 manufacturer recomended). My retraction parameters are below. Can you recommend some changes, jerk and acc parameters for this extruder configuration?
@David_Sherwood Thanks for answer. Reducing speed to 35mm/s little helps but still is something to correct. What do you think about retraction extra prime amount about 0,06mm3? (for 0,4 nozzle it’s about 0,5mm filament.
My 2 cents… for my bowden extruder I am retracting at 50mm/S, priming at 15mm/S with 0.15mm3 of extra prime amount. And, yes, for PETG you need to print slowly compared to, say, PLA. I am getting excellent results with PETG on blue tape. Temps are 235/70 print, 240/80 first layer.
Great! Thanks for your reply 
You may also benefit from a slower prime speed. Say 40mm/s, and 20mm/s prime. It’ll just cause the nozzle to sit a moment longer before starting the line after a retract, move, prime.
BTW I meant 40mm/s retract and 20mm/s prime. The goal of the asymmetry is to relieve the pressure as soon as possible, but give it a moment to reheat on the way back down.
Different strokes for different folks etc. but for me on my Kossel Mini I had to settle for 30mm/s retraction speed before the filament stopped slipping (sometimes) – I was seeing similar effects to those you are seeing – it doesn’t just slip on retract, it then slips a little afterwards as the extruder has eaten a chunk out of the filament whilst slipping and so it slips some more, briefly. In my case i could hear it happening.
