Do I have a tension or humidity problem?
Recently my mini started stuttering while printing, causing prints to fail, or under-extrude. When I took apart the assembly I found the filament was being ground between the gears. This isn't the first time I've opened it to look inside and clean the feeder gear. Did I put everything back together too tight? Or is this caused by something else? Picture for reference. 
RE: Do I have a tension or humidity problem?
Alas, a problem I guess most Mini owners have seen at some point. The Mini is sub-par. I’d start by making sure the idler screw is not one bit tighter than absolutely necessary.
A more costly approach is to upgrade it to a Bondtech dual drive extruder which in my hands seems more forgiving.
Formerly known on this forum as @fuchsr -- until all hell broke loose with the forum software...
RE: Do I have a tension or humidity problem?
In my case the mini can be adjusted to work very well. You may get such filament grinding if it is too loose or too tight. Drying the filament always helps.
Regards,
Mark
RE: Do I have a tension or humidity problem?
I've been having issues with my Mini doing similar things, in my case I was seeing under extrusion as if the nozzle were clogged, I changed PTFE tubing in the heat break and even the nozzle without improvement, I finally concluded the problem was the filament itself. The problematic filament seems to work fine in my I3, but that is a dual gear direct drive nozzle which seems a little more forgiving with bad filament.
One of the things I've seen with problematic filament is it is brittle and breaks like dry spaghetti. I don't know if this is due to moisture exposure or inconsistent manufacturing, but it seems common that when the Mini has a problem the filament is brittle. Brittle filament may be what is causing the feed gear to skip and fill with dust. I use compressed air to blow out the dust, I unload the filament, sent the extruder motor spinning and blow out the dust while it does then reload and go.
I hope some of this may help, I've been around and around on this and right now my printer is printing happily along, it seems to like the filament it's printing with now.
Cheers
-Bob
Prusa I3 Mk2 kit upgraded to Mk2.5s, Ender3 with many mods, Prusa Mini kit with Bondtech heat break, Prusa I3 Mk3s+ kit
RE: Do I have a tension or humidity problem?
I've been having issues with my Mini doing similar things, in my case I was seeing under extrusion as if the nozzle were clogged, I changed PTFE tubing in the heat break and even the nozzle without improvement, I finally concluded the problem was the filament itself. The problematic filament seems to work fine in my I3, but that is a dual gear direct drive nozzle which seems a little more forgiving with bad filament.
One of the things I've seen with problematic filament is it is brittle and breaks like dry spaghetti. I don't know if this is due to moisture exposure or inconsistent manufacturing, but it seems common that when the Mini has a problem the filament is brittle. Brittle filament may be what is causing the feed gear to skip and fill with dust. I use compressed air to blow out the dust, I unload the filament, sent the extruder motor spinning and blow out the dust while it does then reload and go.
I hope some of this may help, I've been around and around on this and right now my printer is printing happily along, it seems to like the filament it's printing with now.
Cheers
-Bob
You are absolutely right there. The Mini is picky about filament. It does not do well with filament that has a large variation in diameter and there are some it just doesn't like for reasons I don't know. I just use another kind and can give the kind it doesn't like to a friend with a direct driver extruder. I use the various Prusa fiaments and Azurefilm PETG mostly.
Regards,
Mark