DIAGNOSIS The depth adjustment lever's clamping force is insufficient. The serrated washer or the lever mechanism is worn or loose.
FIX Locate the depth adjustment lever pivot bolt. It's on the front of the shoe. Tighten this bolt a quarter-turn with a hex key. Test the clamping action. It should lock firmly without excessive force.
IF THAT DIDN'T WORK The serrated steel washer behind the lever is worn smooth or cracked. You must disassemble the lever to replace this washer. The part is a lock washer.
HEADS UP A slipping depth setting is dangerous. It can cause kickback or blade binding. Do not use the saw until the lock holds securely.