Bulldog, Which model do you have? There are many different styles. I have 2 Craftsman routers. One has a depth adjustment ring that rides on ball bearings. It may or may not be the same as yours. If you get any build up of sawdust under the plastic collar it slips, and is difficult to adjust. You need to remove the motor from the base to clean it. When you do be prepared for the ball bearings to go flying. It's loads of fun trying to get them back in the groove they ride in. Another possibility is the ball bearings have slipped out of the groove. I had trouble on mine with this. Again, cleaning and careful reassembly is in order. Make sure the cam tensioner is tight when flipped to the lock position. Hope this cures the slipping but dont hold your breath.