I did receive a response from the Pegas repairman. This is the quote. Sometimes dirt and grime get in the threads, I have had a few customers complain about this, if you loosen the set screw on the knob, remove it and clean the threads, then reinstall everything back it should hold. There was only one customer that needed to use thread lock on his but that was an old machine and he didn't want to attempt to do any of my suggestions.