If you come across a stiff Knurled knob on a Dunham. Remove the collet closer, Place on a bench and remove the rear snap ring. Turn the collet closer vertical and, on a piece of wood, drop on the threaded end of the draw bar and Bearing , and draw bar will come out of the bearing housing. Next look inside the housing and you will see an “O” ring, with a hook remove this “O” ring and estimate how much it has “swelled”

Put it on a expanding Arbor on a lathe and turn the OD down Reinsert the “o” ring and try it .If enough material has been removed it will free up the Knurled Knob. Re-assemble the collet closer and reinstall on the machine and Adjust the runout .