I've used 1.75mm filament in my printer and most times it works fine, but once in a while the smaller and more flexible filament will bend and bind up between the drive gear and the print head. I've found that using a little higher temp on the print head helps to keep this from happening, the filament softens and flows with less back pressure on the filament helping to keep it from folding up. I've since used up my smaller diameter filament and switched to all 3mm. Awesome post, awesome printer,