It's not uncommon for a drill chuck to become a little out-of-whack and, as a result, not completely close. At best, this failure to close can be obnoxious; more often than not, though, it can really clam up your productivity. This is not good. – Keep your drill tight and your mood above water with these few steps that will help you quickly close your whacked-out chuck.
First Things First:
As you know, you will find a chuck screw at the center of an opened drill chuck. This screw is responsible for a large part of keeping your chuck where it's supposedly to be. Like all things with a job to do, though, sometimes these little screws can lose their way. Sometimes, the screw may be lost altogether, but, in either case, it just needs a little direction. Because a loose or missing screw will prevent the chuck from closing entirely, you must tighten or replace the screw. Remember, that this screw is reverse threaded. So, to tighten the thing, you must flick that wrist to the left (counter-clockwise) and spin the screw in a counter-clockwise motion. Once the screw is good and tight, the chuck should close and grip as it's meant to.
Coming Back for Seconds:
If the chuck remains loose or continues to revert to the out-of-whack position after you have tightened the chuck screw, there are a few other factors that might be at play – first, the screw or the screw-hole itself (inside the chuck) may have stripped threads. This would prevent the screw from staying in place which, in turn, advances the chuck from keeping tight. If the screw threads are stripped, replacing the screw should do the trick. If the screw-hole inside the chuck is stripped, though, you probably need a new chuck.
For one or another reason, the chuck may also be locked or rusted into a loose position – or – the fingers inside the chuck may have slipped, slouched or broken preventing the chuck's jaws from gripping a bit. – In these cases, you pretty much need to either replace the chuck or have the thing professionally inspected.
Now that we've reached the end of this tale, I think the moral of the story is, "keep your screws tight (or you'll end up with a screw loose," – yes, pun intended). Good luck with your chuck and remember that tight drilling requires a tight drill (chuck).