Lock Spins in Commercial Glass Door

If you a have a commercial glass door with a lock cylinder that is about 1 inch in diameter, you will have loosening. This happens because your door is being used! Not a bad thing! But, vibration causes all kinds of issues in doors and locks. Here is what you can do if your lock is spinning in the door. You will need a Phillips Screw Driver and a small, flat-head driver.

1. Walk over to one of the businesses next to you and observe the position of the cylinder. You will note that the key insertion point is probably at the 6 o' clock position exactly. (Some door have in at 12 o' clock, but it is rare.) Also, make sure you are not looking at a door on the business where the lock cylinder has been turned upside down in order to disable the key operation on the outside. If in doubt, ask the store manager. 
2. Open your door and look on the door edge and you will see a cover plate with three screws in a vertical line. Using a screwdriver, remove these screws and remove the plate.
3. Look for a small, black set screw that sits flush into the lock, right next to the cylinder that is loose. Back the screw out counterclockwise two turns, but do not remove it.
4. Grab the cylinder. It is a threaded lock cylinder and it screws in and out like a regular screw. Turn the lock to where the key insertion point is sitting right a 6 o' clock.  Tighten set screw. While you are at it, tighten both. You will see them side by side.  Replace plate.
5. Since you are servicing the lock, take WD-40 and shoot the key hole. Also, with the deadbolt in the partially "out" position, angle the WD-40 can into the bolt hole and aim in up into the lock where you guess the back of the lock's key cylinder would be.