put the drill in speed setting 1 before you continue~!
Step 1. This step loosens the screw inside the chuck. Open the chuck
all the way — if you see a screw inside, it’ll need to come out before
you can remove the chuck. If there’s no screw inside, you can skip
steps one and two.
Step 2. If there’s a screw inside the chuck, typically the threading
will be left-handed, so turn it clockwise to remove it. Be careful, and
use the right size screwdriver — you don’t want to strip the screw.
Step 3. Insert the largest hex key that you have into the chuck,
short-side-in, and tighten the chuck. Tap the hex key sharply in a
counterclockwise direction to loosen the chuck. Now you can remove it
by hand.
This won’t work for every consumer drill ever made, but pretty
close. Most drills will match one of two common chuck-threading
standards: 3/8′-24 threaded mount for 3/8′-capacity drill chucks, and
1/2′-20 threaded mount for 1/2′-capacity drill chucks — but on some
drills just the opposite may occur. To be safe, always check the thread
count before you buy a replacement drill chuck.