Quick answer
- If the bit slips but the chuck stays put, the jaws are dirty or the bit isn't centered. Clean the bore, center the bit, and ratchet the chuck until it clicks several times.
- If the whole chuck keeps backing off the drill, there's often a hidden retaining screw inside it, and it's left-hand threaded. Turn it counterclockwise to tighten (clockwise loosens it). Remove the battery first.
- Round-shank bits slip more than hex-shank bits. If one bit keeps spinning, the bit is often the problem, not the drill.
First, figure out what's actually loose
"Chuck won't tighten" covers two completely different problems, and the fixes don't overlap.
The common one is the bit slipping while the chuck body stays in place. That's a gripping problem at the jaws. The rarer, more confusing one is the entire chuck unscrewing from the drill spindle, so the whole assembly wobbles or falls off in your hand. That's a retaining-screw problem deep inside the chuck. Sort out which you've got before you touch anything, because tightening the jaws harder does nothing for a chuck that's leaving the spindle.
Fixing a bit that slips
- Clean the bore and the shank. Open the jaws all the way and wipe out the inside of the chuck and the bit shank. Grease and drilling dust are the number-one reason jaws can't close fully on the bit.
- Center the bit and ratchet it down. Stand the drill upright on the bench, hold the bit straight and centered, and tighten until the chuck is snug and ratchets, and check your drill's manual for how its chuck is meant to lock. One twist until it feels snug isn't enough.
- Seat hex shanks on the flats. If you're running a hex-shank bit, make sure the jaws land on the flats, not perched on the corners. On the corners it'll wriggle loose every time.
If a bit still spins when the jaws are clamped and clean, the bit is likely too small for that chuck, or the jaws are worn. Switch to a correctly sized hex-shank bit before you blame the drill.
Fixing a chuck that keeps unscrewing
This is the one that sends people to buy a new drill they don't need. Remove the battery first. On many reversing drills there's a retaining screw at the bottom of the bore, behind the jaws, holding the chuck on the spindle.
Open the jaws all the way and look straight down inside. If you see a screw head, that screw is left-hand threaded, so it works the opposite way to a normal screw. Turn it counterclockwise to tighten it. Turning it clockwise backs it out (DeWalt's support page says clockwise removes it), which can let the chuck work loose. Snug it down firmly and the chuck should stay on the spindle.
Most troubleshooting articles skip this screw entirely and just tell you to "tighten the chuck harder," which is useless when the problem is the chuck leaving the spindle. The left-hand screw is often the actual fix.
Why a good chuck loosens mid-job
If everything's clean and tight but the chuck still creeps loose while you work, check the retaining screw described above and the condition of the jaws and spindle threads.
When to just replace the chuck
If the jaws are visibly worn, scored, or won't grip a known-good bit even when clean and fully ratcheted, the chuck is done. A replacement keyless chuck is inexpensive and threads onto the same spindle — just match the thread size (1/2-20 is common on cordless drills) before you order. That beats fighting a worn chuck that'll never hold a bit straight again.