I bought a Milwaukee 5378 7.5 amp hammer drill. I notice that whether I use the drill in hammer mode or rotary mode, and regardless of the drill bit or the medium (brick, concrete, wood), I have to constantly retighten the bit. I'm careful to position the bit correctly and to tighten at each of the three points on the chuck, but the bit still comes loose. (Not loose where it falls out but where it does need to be retightened.) I've had the drill for about a year, and it has not had heavy use. I bought Milwaukee because the company has a reputation for quality. But having to constantly retighten the bit is really annoying. Is there something I can do to correct this?

sounds like a sloppy chuck. have you contacted Milwaukee Tools warranty folks yet? that's the thing to do.

Could be that there is some debris caught up in the innards of the chuck. Try moving the chuck all the way in and out without anything in it - maybe add a small squirt of WD40. If the tangs of the chuck are binding at all then it could keep it from tightening all the way.

As an aside, it is very common for hammer drills to need to be tightened really hard - I will often use a few light taps with a hammer on the key. This is because the vibrating hammer motion will tend to loosen up the chuck. But, that only a factor when it's in the hammer drill position.

Really need a SDS drill if your going to be doing a lot of drilling in concrete.