Notifications
Clear all

[Solved] Repeated filament breaks inside the hotend PTFE tube  

  RSS
mikeolson
(@mikeolson)
Active Member
Repeated filament breaks inside the hotend PTFE tube

Howdy folks,

A couple of weeks ago, my PLA filament failed to unload properly on the i3 MK3S. I wound up with a blob that broke off inside the PTFE tube, but high enough above the hotend that I couldn't melt it out by turning the temperature up high. With help from @jsw and @diem I diagnosed that problem, disassembled the printer to the point that I could get at the hotend, and carefully removed the occlusion from the PTFE tube.

This has just happened again. I'm about to repeat my disassembly, and hope that I'll be able to extract the blockage again.

This is super frustrating. Any ideas on why this happens to me repeatedly? I've been very careful not to use force in extracting the filament from the printer since the last time this happened. Could there be a problem with the PTFE tube, the hotend or the idler? Is there some likely user error I'm making?

Posted : 12/02/2023 7:53 pm
mikeolson
(@mikeolson)
Active Member
Topic starter answered:
RE: Repeated filament breaks inside the hotend PTFE tube

I got the printer disassembled and pulled some gunk out of the PTFE tube. I've reassembled, and still can't load filament. I now believe that the tube alignment is bad. I need to pull the printer apart again and verify/fix alignment. I'm gonna mark this solved while I do that, no use speculating on causes yet.

Posted : 12/02/2023 11:06 pm
Diem
 Diem
(@diem)
Illustrious Member

Your Bondtech gears may be a fraction out of alignment, you may have a damaged PTFE tube in the extruder or perhaps the tube compression collet at the top has failed or was incorrectly fitted.

Cheerio,

Posted : 13/02/2023 7:35 am
mikeolson liked
SG Newb Rider
(@sg-newb-rider)
Trusted Member
RE: Repeated filament breaks inside the hotend PTFE tube

get a new PTFE tube, they're cheap and not worth the effort to save. buy the good quality ones by the meter and you'll have tons to spare

Posted : 14/02/2023 2:49 pm
mikeolson liked
mikeolson
(@mikeolson)
Active Member
Topic starter answered:
RE: Repeated filament breaks inside the hotend PTFE tube

Closing this item out:

The problem was indeed a bit of broken filament inside the PTFE tube. I did a poor job clearing it and had to disassemble the printer again to get the last bit out. I did, and now it's printing well. I'll absolutely lay in some spares, though!

One thing: I have decided I will only change the filament immediately following a print job, when the filament's still hot inside the PTFE tube and hotend. I have designed a tiny little object that I can print in 30 seconds. Once it's printed I immediately hit "Unload filament," and it comes out easily and cleanly. My filament changes have been going well (knock wood!) since I started doing that.

Posted : 14/02/2023 5:15 pm
Diem
 Diem
(@diem)
Illustrious Member

I didn't realise you were unloading cold - use the preheat function on the LCD menu.

Cheerio,

Posted : 14/02/2023 6:45 pm
RandyM9
(@randym9)
Honorable Member
RE: Repeated filament breaks inside the hotend PTFE tube

I may be mis-remembering but doesn’t the printer menu prompt you for a pre-heat setting before attempting a ‘cold’ unload routine? I’m not at my printer’s location or I would try this myself. Nonetheless, solid advice to make sure the printer is up to proper material temp before attempting to unload.

Posted by: @diem

I didn't realise you were unloading cold - use the preheat function on the LCD menu.

Cheerio,

Cheers

Posted : 14/02/2023 10:32 pm
jsw
 jsw
(@jsw)
Famed Member
RE: Repeated filament breaks inside the hotend PTFE tube

Yeah, I thought the printer would wait for temperature before unloading.  I do unload/reload all the time with no issues at all over the years, but there is the lag for the nozzle to heat to something like 95% of the filament temperature.

Incidentally, when changing from one species of filament to another, I always heat to the higher temperature of the two and leave it there until the newly-loaded filament is purged and ready to go.

One exception.  PC Blend.  Learned the hard way.  Do NOT let it cool down and let it sit in the machine overnight at room temperature.  I always unload that immediately after I've finished printing with it.

Posted : 15/02/2023 2:41 am
mikeolson liked
mikeolson
(@mikeolson)
Active Member
Topic starter answered:
RE: Repeated filament breaks inside the hotend PTFE tube

The printer does preheat before unload, but I still occasionally got the breakage. Good advice to preheat and then wait a bit.

Posted : 15/02/2023 6:13 am
Share: