Home Improvement

How to Fit a Door Lock

Like it or not, sooner or later, you will have to fit a new lock on your front door. Perhaps you bought a new door, and now you need a lock. Or maybe you moved to a new apartment and don’t feel like the lock is secure enough. In most cases, you would be able to do this by yourself, provided you have the right kind of tools. And since tools are nothing without knowledge, here is all you need to know about how to fit a door lock by yourself.

If you:

  • Are replacing your old door with a new one and need to buy a new lock as well;
  • Are moving into a new property and want to change the old, worn down lock;
  • Had a roommate leave and want to change the front door lock as an extra measure.

Then read along…

Table of Contents:

What is the difference between a mortice lock and a cylindrical lock?

Before you learn how to fit any type lock, you need to be aware of the two most common types. Chances are you will be fitting or replacing one or the other.

Cylinder lock

The locking mechanism uses a series of pins, hence why cylinder locks are also called pin tumbler locks, which follow the key pattern key. When you insert the key into the hole, each pin moves into its respective position allowing you to turn the key and lock or unlock your door.

Cylinder locks are relatively inexpensive to replace and easy to fit. There are two types of cylinders:

  • Euro cylinder locks – These are shaped like a large keyhole, or as some people see them, like a lightbulb. Euro cylinder locks come in various configurations, from one to two side key operation. They all have the same size and scale, but different models vary by the length of the cylinders, the location of the moving “cam”, and the fastening screw-hole. Nowadays, these locks are pretty popular in the UK, because of their practicality and the fact that new uPVC and Composite doors all mostly operate with euro cylinders.
  • Oval cylinder locks – These locks operate the same way as Euro cylinder locks. The difference is that they are oval-shaped. Their name fits quite well in that regard, no pun intended. Oval cylinder locks may have key-operation (one cylinder) on one side only or both sides (double cylinder) depending on what you need. Chances are you will need neither, though, as these locks are rarely used in the UK anymore and if you are replacing a lock, it will probably be a different type.

Mortice locks

This kind of lock requires a pocket (the mortice) for it to be fitted in. The pocket always needs to be cut out of the door beforehand. That’s why mortice locks don’t work too well with wooden doors. So much material needs to be cut out, that the door becomes fragile and easier to break. Mortice locks work best when fitted on metal doors because both items are pretty sturdy. In general, these locks are better suited for high traffic areas where doors are frequently opened, closed, locked and unlocked.

Two sorts of mortice lock are available:

  • Sashlock – It has a bolt, a latch and a pair of handles so you can open or close the door from outside or inside your home. The latch keeps the door closed, without the need to be locked.
  • Deadlock – this one has just a keyhole and a bolt, no handles. So, unless you have a key, you cannot open the door.

If you are interested in learning more about door locks, head over to our post on the matter. There you’ll find what types of door locks exist, how do they work and look.

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Preparations before fitting a door lock

Before you get down to the lock fitting process, make yourself familiar with some safety precautions. Also, the following tips would hopefully save you some headaches along the way.

  • When drilling, wear safety goggles;
  • When chiseling, wear safety goggles, protective gloves and be sure to chisel away from your body;
  • If you are replacing a mortice lock, you need to make sure the new product is compatible with the mortice in your door. Bring the old lock with you when buying the new one, it will be easier to decide what to buy;
  • Replacing euro cylinder locks is less troublesome since they all have the same shape, but you need to find one which is the same length;
  • Use only screws provided or recommended by the manufacturer;
  • Keep locks clean and lubricated with products suitable for their material and finish;

Need a locksmith? Click more to learn how Fantastic Services can help you out!

How to fit a cylinder lock

When it comes to PVC windows and doors, you already have the necessary fittings to install or change a cylinder barrel. On the other hand, if you want to fit a cylinder lock into a wooden door, then you’d have to drill the space yourself.

  1. Mark the position of the lock body with a pencil. Mark out the entire shape as well as the shape of the lock.
  2. Mark where the faceplate will be on the edge of the door. Pencil out the screw holes in it too.
  3. After putting down the faceplate, draw a line from the top hole to the bottom.
  4. Drill through the wood using an auger drill bit (it is specially designed for drilling wood). Use a drill slightly wider than the lock body.
  5. Drill a series of holes.
  6. Chisel out the space between the holes.
  7. Put the lock body inside the cavity to check if it fits properly and chisel out some more material if needed.
  8. Remove the lock body and drill holes for the lock cylinder.
  9. Drill holes for the backplate screws
  10. Install the backplates
  11. Insert the cylinder mechanism into the door from the outside. Depending on the brand you have purchased, you may have an indicated side for the outside part of your door.

How to replace a cylinder lock

Start by measuring the length of your current lock. 

  1. Open the door.
  2. Find the center screw.
  3. Measure the distance between the center screw and the face end of the lock on each side. The sum of those lengths is the length of your cylinder lock.

Now when you have your new lock:

  1. Open the door.
  2. Remove the lock fixing screw.
  3. Place the key into the lock and turn slightly on both sides. This will allow the cam tongue to line up with the body of the lock.
  4. Push and pull the lock gently. If the cam tongue is lined up with the lock, you will be able to pull out the cylinder with the key.
  5. Place the new lock and repeat all the steps in reverse order.
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How to fit a mortice lock

The installation process is the same for both sash locks and deadlocks. Mind you; different mortice locks are designed for different door thicknesses. You need to purchase the best-suited lock for your door. Otherwise, you may damage the door whilst cutting out the mortice.

If your door has a horizontal mid-rail, be sure to position the lock in the center of the rail.

  1. Place a wedge under the door to keep it steady while working.
  2. Place the body of the mortice lock on the door and mark with a pencil. Mark out the top and bottom edges of the body as well as where the keyhole and handle holes will be. 
  3. Drill holes into the door according to the marked areas. For the keyhole, drill the top hole and finish the rest with a thin pad saw. This saw will give you more precision when forming the shape.
  4. Place the faceplate on the door edge and mark out its shape as well as holes. Connect the holes by drawing a straight line with your pencil. Now you are ready to drill out the cavity for the lock.
  5. Select a spade bit that is slightly wider than the lock body. This will ensure the body fits more easily into the cavity once it’s drilled out.
  6. To make sure you make the mortice with the right depth, line up the drill bit against the lock body. Mark the depth on the shaft by frapping it with some masking tape.
  7. Drill several holes into the edge of the door. Drill them one below the other along the pencil line you drew beforehand.
  8. Chisel out between the holes and smooth out and rough edges.
  9. Attach the faceplate to the mortice lock and place them into the cavity. Additional chiseling may be needed until the lock body fits it snuggly.
  10. Mark the edges of the faceplate with a Stanley type knife.
  11. Chisel out the wood following the markings. Take out small amounts at a time and don’t make it too deep. The point is for the faceplate to fit into it.
  12. Insert the lock body into the mortice and screw it in.
  13. Install the handle and key plates using the screws and bolts provided by the manufacturer.
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How to replace a mortice lock

Before you purchase a new lock, measure the distance:

  1. From the front edge of the door to the centre of the keyhole
  2. Between the keyhole and the door handle spindle hole;
  3. The height of the faceplate.

If possible, it’s best to have your old lock with you when looking for a new one. This is how to remove it:

  1. Open the door.
  2. Unscrew the screws holding the faceplate.
  3. Remove the door handles and the spindle holding them together.
  4. Holding the bold with a pair of pliers, pull out the lock body.
  5. Place the new body into the mortice. Some adjustments of the cavity with a chisel and hammer may be necessary.
  6. Remove the old keep from the door frame and place the new one. Again, you may need to adjust the space with the chisel and hammer, so the new keep would better fit.

Call in professionals

If you lack the time or tools to fit a door lock, why not get professional help? Book a lock installation & replacement expert and get the job done in no time. Fantastic Services works with skilled and fully-equipped locksmiths situated all around London. Whatever door lock you need installed, we can take care of it in a stress-free manner. No need to worry that you might accidentally damage your new door or waste numerous hours trying to figure out what size drill bit is the best. Arrange a visit from a locksmith today and get this task out of your way.

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  • The most common locks are Euro cylinder and mortice locks.
  • Replacing euro cylinder locks is less troublesome since they all have the same shape. With mortice locks, you have to pick a lock that fits the current pocket in your door.
  • Decide what kind of lock you need in accordance with your door and traffic levels.

You might have decided that entrusting the job to an expert is the best course of action. If so, take a look at our helpful post on locksmith prices in the UK! There, you’ll learn how much you can expect to pay for the service.

Image Source: Shutterstock / Oleksandr Pirko


Do you have a door which needs a new lock? What other information do you need to do it? Let us know in the comments below!

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