Filament Drive Tension Slipping?

[sthone]

Just so you know.... you're chasing ghosts worrying about drag on the spool... the extruder can and will actually pick that whole spool right off the spool holder and fling it around/pull it right up to the top of the press. (I speak from experience.) Whatever design you go with for the filament drive always print an extra one before you need it. They all eventually wear out. (such as the filament will eventually oblong the feed hole.)

[Gwhite]

That's the plan after I get some polycarbonate & get it printing nicely. There seems to be an availability issue with black 1.75mm PC at the moment. Amazon is out of stock on ePC, and Polymaker is out of stock on just about all flavors of PC-Max & PC-Plus.

I'm still trying to decide which one I would prefer. Lots of people rave about the ePC in natural, but the reviews of the black version are more mixed. PC-Max has good reviews, but is apparently harder to print with.

[Gwhite]

Well, I got my new drive from MakerGear, and installed it last night. Once I had the old one off, I could see the problem. Because the drive gear was too far back, probably combined with twisting of the bearing due to the offset support, the filament had been pushed forward inside. It wore a large groove in the top section of the drive:

and a slightly smaller one on the lower end:

All of this was happening inside the drive, where it was impossible to see without taking everything apart. Basically, the filament was coming down, and bending around the front of the drive gear.

One possible way to avoid this in the stock drive design would be to use a smaller bearing, with a grooved sleeve like in this thread:

http://forum.makergear.com/viewtopic.php?f=10&t=3210&p=23537&hilit=filament+drive+bearing#p23535

The stock bearing is 5mm bore, 5mm thick, and 16mm OD. McMaster Carr has a 14mm OD bearing (#7804K109). It should be possible to make a press on sleeve with a small groove to keep the filament from wandering sideways.