Recently I had this problem where I needed to change filament from PLA to PET-G or similar. And... filament jam. After playing around with different settings and speeds and still getting the same results I had to clean everything. And again during a print, it jammed.

I brought a new nozzle, heating cartage, Teflon (PTFE) tube and some additional components(fans, new wires and so on) but still was the same. Now I'm waiting for a new set of hotend Mk8Design Needed kit.

A week after the order and still waiting, I played with retraction a little. By default, it was set to 0.8 mm on Sli3er but I had set it to 4-6 mm because it gives the best results and no stringing. I changed it again to 1.5-2 mm and... no more jamming at the cost of getting stringing. I'm using PLA which I never had experienced strings before.

So, in summary, the problem occurs due my retraction setting. Either I have to live with strings and no jam problems or no strings but jamming problems during printing.

Have someone had same problem as me? How did you fixed it?

  • Printer AlfaWise U30(bowden type) but it's no longer the same.
  • Motherboard: MKS 1.4 Gen A4988 + DRV8825 Stepper drivers(no problems here)
  • PID(Autotune), Calibrations and so on done correctly.
  • Firmware latest marlin 1.1.9 (Tried bugfix but the same)
  • Sofware for slicing PE Sli3er (Tried Ultimaker Cura with same model and same problem)
  • $\begingroup$ Would you please provide some additional things to make it easier? You said Mk8, do you mean a Makerbot Mk8 Hotend? Or did you update to an all-metal hotend? What is your standard printing temperature? What is your retraction speed? $\endgroup$
    – Trish
    Commented Jul 13, 2019 at 17:49
  • $\begingroup$ There are more settings to fight stringing, e.g. lower print temperature. PETG is more prone to stringing opposed to other types of plastic. $\endgroup$
    – 0scar
    Commented Jul 13, 2019 at 17:49
  • $\begingroup$ I wrote what I changed. I haven't touched the hotend. It is original what Alfawise had. They used makerbot mk8 hotend (I believe so) but not quite sure about. Because of that I ordered a new one and different. Alfawise doesn't like to share information about they products. The firmware wasn't open source like marlin. Sorry about the temperature or printing. For PLA is 200-220(recommended) So between those temp. It's still the same. Retract is default in sli3er (35mm/s) I tried from 25 to 50 and nothing... same $\endgroup$
    – fluSneez
    Commented Jul 13, 2019 at 20:12
  • 1
    $\begingroup$ The most accurate link to hotend: amazon.com/Longer-Printer-Extruder-Creality-Alfawise/dp/… $\endgroup$
    – fluSneez
    Commented Jul 13, 2019 at 20:21
  • $\begingroup$ Not an answe, but assuming PTFE is a bowden setup, you definitely need at least 4-6 mm of retraction to avoid stringing. 0.8-2mm is not going to cut it anywhere but a direct drive extruder, and I'd be doubtful that it's even really sufficient there. So you should try to fix this right. $\endgroup$ Commented Jul 14, 2019 at 4:11

1 Answer 1


I had problems with jamming PETG due to retraction. My model had many retraction moves, such that the amount of filament used during a printing move was less than the retraction distance. I found that several trips through the feed gear flattened the filament, which caused two problems.

  1. The flattened (or ovaled) filament had trouble fitting through the round holes and tubes, and
  2. Since it was thinner, the filament was not gripped as tightly so there was less force pushing it.

I reduced my feed gear pressure and the problem stopped.

PETG is not as stiff as PLA. The multiple trips through mangle flattened it.


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