I got into the habit of wiggling the chuck to see if it was loose from the adapter. Yep, again after tightening it two days ago. I pondered what to do. Drawing on experience of the past. I removed the set screw and dropped a #5 lead shot into the hole. Tightened the screw. Have done this in the past on some other things and no problems with the screw loosening. The shot conforms to the threads.