Extruder tension knobs slipping

Hi All,

Not sure if this has ever been asked (didn’t find anything in a quick search). I have been having on-and-off issues with the common problem of having extrusion quit in the middle of a print due to the hobbed bolt stripping the filament. I’ve gone through a lot of adjustments to try to address this, and generally have the problem minimized.

However, I had a print going last night, and this morning extrusion had quit and the filament was stripped again. What I noticed for the first time, though, was that the idler tension knobs seemed to have loosened considerably from where I had set them yesterday morning. FYI, I had loaded the filament yesterday morning, tightened the knobs, and did a number of successful shorter prints throughout the day.

So, now I am wondering if my problems in this area are due to the idler tension knobs slowly working their way loose over the course of several prints. I have not seen any discussion of this anywhere. Has anybody else noticed this happening? If so, have you noticed any correlation with stripped filament? And, more importantly, have you come up with any solution to keep the knobs from working loose?

Dave Levi

The knobs can work their way loose, expecially if you accidentally lubricated them. You want 8mm between the washers on either side of the springs as a starting point. If the bolts are working loose, get some replacement bolts and nuts and swap them out, or alternativly put some blue loctite on the exposed threads sticking out of the far side of the nuts. The one closest to the motor frame you might just have to kind of drizzle in from the top.

I used to have the same problem and made a small item that pushes on to the tensioner knobs and prevents any movement. STL file attached.

Cheers
Sam
Tensioner Lock.stl (3.65 MB)

Thanks guys, I’ll try that tensioner lock first.

If the hobbed bolt is “eating” through the filament, this could be a signs of a clog, partially blocked filament path or signs of worse things to come.

What type of filament? If its PLA, then you’ll want to double check that you’re not experiencing heat creep from the lack of cooling of the heatsink. If enough heat travels up the all-metal hotend, the filament will swell when close to melting… and clog the hotend.

If ABS, then a few more turns on the tensioner knobs should help. The springs between the idler and tensioner knob should keep the screws from slipping. Piercet’s advice of ~8mm between the knob and idler is good. Heat creep won’t affect ABS as much due to the higher melting point.

I’ve noticed on my machine (after 9 months), the extruder body and hotend may need “re-alignment” to ensure a smooth path for filament. I feel a slight “obstruction” impeding the filament as it feeds into the hotend… more tension on the idler helps this as well. It could also be the “teeth marks” from the hobbed bolt catching somewhere along the path.