How to fix a rubbing knob
You discover that one of the knobs on your Silver Bullet is a little stiff to rotate, or that it has too much resistance at certain settings.
What you are experiencing is an interference between the knob skirt and the surface of the faceplate. This can be caused by two things. If it's a brand new unit this can be caused by the external face of the knobs pushing up against the plastic bag in which the unit is wrapped as the unit shifts around during transit. This occasionally happens on long overseas journeys with lots of handling, especially if the bag is wrapped a little too tight. The other cause is from pushing the knob against the faceplate during normal use.
Thankfully the fix is very easy. Simply pull the knob away from the faceplate to create more clearance. The potentiometer shaft is a D-shaft and does not use a set screw, so the knob is pressed on and held with friction. No tools are required other than your fingers and a firm pull on the black portion of the knob. You may pull the knob off completely if you wish and push it back on. During production we set the skirt spacing by inserting a plastic business card between the skirt and the faceplate and then pressing the knob up against the card. You may use a plastic credit card to do the same thing.