Filament is grinding on the geared bearing

Hi - I’m getting an issue where the filament has a big gouge ground into it from the geared bearing at the top of the extruder, right where that sharp bearing gear pushes the filament in. What causes this? It doesn’t always do it. Seems to lose traction pushing in the filament at times, and then grinds a big gouge in the filament, and then can no longer feed filament.

A couple of things. To start, that “geared bearing” is actually a Hobbed Bolt. it’s a nirmal 8mm bolt, with hobbs ground into it. That bolt passes through two seperate 608zz bearings. The idler arm has an idler bearing on it, and that bearing pushes the fillament against the hobbed bolt. The two bolts with springs on them at the top of the extruder are called the Idler Arm Tension Spring Assembly, and you adjust the level of tension that the Idler arm places on the fillament in contact with the hobbed bolt by turning those bolts tighter or looser.

You want to start with 8mm distance between the washers on either side of the springs on the idler arm tensioner bolts. Sometimes you will need it tighter, sometimes looser. if you have it at 8mm for both bolts and it is still doing that gouging, try turning the bolts to increase the tension. If that doesn’t work, you may be printing too close to the bed, which can cause the molten plastic in the nozzle to back up and stop the solid plastic. Molten plastic is not a compressable liquid, so if it can’t go anywahere, and you try to push more material into it, it’s basically like trying to extrude through a brick wall.

if you are printing ABS plastic, and the material is lifting up from the bed, that can cause the same issue. Overextrusion can also cause a similar effect.

Thanks piercet for the notes. This forum didn’t tell me there was a reply, or this would’ve been really helpful! :wink: I actually pretty much learned everything you mentioned in the interim, including the part names. What I discovered was, the idler block was cracking, and last night cracked clear through. So there was no tension being applied to the filament, and the hobbed bolt was spinning more or less freely against it. Mystery solved. So I managed to find the model for the mini idler black and printed myself a new one with another printer this morning (luckily I happen to have another one at the moment or I’d be out of commish). I put it back together and voila it works great again. I will keep an eye on those tension bolts from now on. How it works makes a lot of sense, I just hadn’t clued in to what was going on yet so actually didn’t have enough tension on even as the block was cracking. I used HIPS to re-print the part at 100% infill, for those of you who find this later. Works fine so far, a few hours later. It’s a fairly flexible material so I suspect it won’t crack in the same way but only time will tell. Wish I could change the name of the thread to be more accurate for those down the road that have the same problem. Thanks again piercet!

Just as a heads up, you can change your notifications in the user control panel under board preferences. You can get email notifications for all the things or none of the things!

You’re welcome! The forum only notifies you of replies with quoted text in them by default. I tend to not use quotes for some strange reason most of the time. Habit probably