The adjustment knob is increasingly difficult to turn on one of the two machine clamps (the other one is fine). The clamps are about a year old. I took apart the clamp in question and thoroughly cleaned it with alcohol - paying particular attention to the threads on the rod attached to the clamp, and the inside of the adjustment knob. Put it all back together, and it’s hard to tell that there was any improvement. Anybody run into this or have any ideas? Thanks.