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Melting/Deforming R4 Extruder Cover on MK3S  

Active Member
Melting/Deforming R4 Extruder Cover on MK3S


i recently upgraded my MK3 with the Upgrade-Kit and self printed R4 parts (gCode from Prusa).

After all calibration, i printed a PLA (210°/62°) benchy for ~2.5h. I noticed that the new R4 "Extruder Cover" starts deforming on the right side. I thought that maybe the self printed parts had some issues, so i printed the Bxtruder Body, Cover and two other small parts again in PETG (240°/90°) for ~4h.

Now the Cover looks even more like its going to melting away within the next few printing hours. Should i be concern about a wrong assembly or something? Somebody else had this melting/deforming extruder cover. I add some pictures of the R4 Cover and my old stock B7 parts that had seen like 24days of printing and no to little deforming.

Posted : 23/06/2019 7:16 am
Bunny Science
Noble Member
RE: Melting/Deforming R4 Extruder Cover on MK3S

Unfortunately, that is a community known issue with the R4 extruder design. You are not alone. Prusa is reportedly going to address the problem. 

Bunnies have a temporary solution that may keep you running until Prusa has a new design.

BS Hot Fins and Anti-sag PINDA for MK3S R4 Extruder

You can print multiple hot fins in PETG as a temporary fix if you can't print polycarb or ABS

A more definitive solution is moving to a completely different airflow design like a BNBSX extruder, but that is only suitable for a well experienced builder.

This post was modified 3 years ago 2 times by Bunny Science
Posted : 24/06/2019 6:04 am
RE: Melting/Deforming R4 Extruder Cover on MK3S

I recently built a skelestruder and actually noticed quite a lot of melting on my R4 parts... X carriage, rear half of the extruder body (not just thin regions, dead center in the thick plastic) and the mentioned fins, in addition to a tiny bit of sag on the ABS fan shroud. Seems R4 has some serious airflow design problems.

Posted : 24/06/2019 10:55 am
RE: Melting/Deforming R4 Extruder Cover on MK3S

I think we may have to also consider low-temp PETGs as culprits too; I'm already seeing some droopage on my skelestruder hotfins after only a handful of prints. I used hatchbox and Amazon PETG which prints around 235 as opposed to other PETGs that print at higher temps (e.g. prusament at 250C)

Posted : 27/06/2019 12:03 pm