The locking knob and its screw tighten a gap. I see in the exploded diagram that there's three washers involved. Unfortunately it's not clear where they actually go. I would think there should still be a small gap in the housing when the lock is tight. Make sure it's actually the router and not just the bit that's slipping, like James mentioned. If it is the base my thoughts are...
The gap is obstructed or there's dirt or oil between the base and the motor. Needs cleaning.
There could be an unthreaded portion of the bolt (the knob can't go further). An extra washer under the knob could help.
The gap could be closed (can't tighten any further). Take out the bolt and file or sand the gap a bit.
The base is cracked. Get another base or a new router.
ps I doubt that the lock locks the adjustment ring. The depth lock on many routers simply works like the belt on pants.
The gap is obstructed or there's dirt or oil between the base and the motor. Needs cleaning.
There could be an unthreaded portion of the bolt (the knob can't go further). An extra washer under the knob could help.
The gap could be closed (can't tighten any further). Take out the bolt and file or sand the gap a bit.
The base is cracked. Get another base or a new router.
ps I doubt that the lock locks the adjustment ring. The depth lock on many routers simply works like the belt on pants.
