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How to Fit a Mortice Lock to an Internal Door

Either replacing a mortice lock or fitting one on a brand new door is a task that might be a little beyond the reach of your average DIY enthusiast. It's a complicated job that should only be undertaken by confident DIYers who are certain that they won't potentially destroy a perfectly good door. Here we'll break the task down into 10, easy to follow steps, which should give DIY hobbyists all the help they'll need, and DIY enthusiasts a handy 'check list that can be used as a convenient point of reference.

mortice bathroom lock

mortice bathroom lock

What You'll Need

The mortice lock itself, a drill, a chisel, some masking tape, something to hold the door in place (a wedge for example), a set square, a hammer and a 16mm long drill bit. Also, don't forget to bring your common sense and a strong flask of tea or coffee!

The Ten Steps

  • Decide exactly where you want the lock to sit and then measure the door's side rails to make sure that the lock you've purchased will fit snugly. If you're replacing a lock then always bring the old lock with you to the hardware store so you can compare and contrast.
  • If you're replacing a lock, move the new lock until it lines up with the face plate of the old lock. If you're fitting a lock on a brand new door then you'll want to fit it roughly a metre from the floor. Use a pencil to mark the top and the bottom of the lock's body on the door, making sure to give yourself a few millimetres of leverage.
  • Using a sharp pencil, draw in a vertical line that will help you guide your drill, then make sure the door is secure. The last thing you want whilst drilling is for the door to be wobbling back and forth.
  • Use a length of tape that measures roughly how deep the body of the lock is (+3mm to give yourself some 'wiggle room') and tape it to your drill bit. This should let you know how far you need to drill. Next, drill a series of holes along your vertical pencil line to the depth registered by the tape. When you're done, use a chisel to smooth out the sides of your lock slot. The smoother the slot, the easier it will be to slide the body of the lock into the door.
  • Set the body of the lock over the slot and use the pencil to mark the edges of the face plate.
  • Now this is where the real work sets in. First remove the lock; you're going to need to make a recess on the edge of your door so the front plate is perfectly aligned. Find a firm, stable hammer and chisel and use them to make some cuts in the wood where the plate will eventually be set. Always make sure that you are holding the chisel with the bevel facing excavation area and make sure you're working inside the pencil line. Once the cuts have been made, ease them out a little and you'll have a recess that's ready for your lock.
  • Hold the lock in place against the front of the door and mark the keyhole. Also remember to mark where the handle will be. Do the same on the other side.
  • Drill through the door with your 16mm drill bit from both sides (this avoids splitting the wood) to create holes for the handle and do the same for the keyhole. For the keyhole you'll need to drill two holes, one above the other with a larger hole on top, and a smaller hole on the bottom.
  • Insert your lock into the slot and tap it in place with your hammer. Next, secure your lock with some screws and attach the screw cover plates.
  • If you're working on a brand new frame then you're going to need to chisel out a space for the 'strike plate' on the door frame. If you're replacing one though you should be able to use the strike plate that's already in place.

And that's it. It might seem simple when you take it step by step but remember, this task is more complicated than it seems so make sure you're 100% confident with your skills before you consider breaking out the toolbox. Good luck!