How To Fit A Mortise Lock

different parts of a mortise lock

Read How to Fit a Mortise Lock in PDF format

Some doors come with locks already fitted but most quality doors will not, hence allowing the owner to choose what type of lock and latch they are going to use. Fitting a Mortise Lock into a door requires a slightly above average level of DIY skill.

It’s actually a fairly straightforward job but it is important to get it right when drilling out the cavity. It’s also worth mentioning you should note the thickness of the door and ensure you buy the correct size lock for it although most lock packages will display the minimum thickness or door required. Here is a guide to fitting a Mortise lock to a door.

  1. Measure the height of the handles on the other doors in the house to decide at what height you would like to fix the lock, ideally they should all match.
  2. Hold the lock against the side of the door at the required height and precisely mark out the shape of the lock body on the door. Also mark out the position of the keyhole and the handle spindle.
  3. Drill out both the holes for the keyhole and the spindle. Use a thin saw to carefully cut out the rest of the keyhole shape beneath the initial drill hole.
  4. Mark the centre line of the width of the door edge, you will use this to centralise the cavity where the mortise lock body will sit.
  5. Now mark out the position of the lock on the edge of the door. Use a sharp chisel to go over the outline as this will prevent delaminations spreading beyond the exact area for excavation. Remember you are marking the area for the lock body not the wider front plate which comes later.
  6. Use a drill to make holes within the area marked out in previous step. Make sure the drill holes are exactly parallel to the side of the door.
  7. After you have made a series of holes use a sharp chisel to excavate the remainder of the wood to leave a lock shaped hole. It should be exactly vertical so the lock will also be vertical. Try fitting the lock into the hole and remove more wood if necessary until the lock fits snugly in to it. Throughout this part of the job be very careful not to break the side of the door as the thickness of wood will be slim and potentially delicate. Penetrating the side of the door will ruin the job and the door.
  8. When the lock fits in to the hole mark out the front plate on the egde of the door.
  9. Starting with the edges use a sharp chisel to excavate the area for the front plate to be sunk into. Typically this will only be a depth of 3mm. Too much and it will look shoddy, too little and it will sit proud.
  10. Fit the lock into its final position within the door with the screws provided.
  11. Now fit the handles onto the sides of the door so you can begin the next and final part; fitting the strike plate to the door frame.
  12. With the door open but the lock in the ‘locked’ position move the door so it is ajar to the door frame.
  13. Using the exact height of the door lock bolt and the door latch mark out the horizontal levels of both on the door frame. This gives you the precise height necessary for the strike plate.door with mortise lock
  14. Now you have the height measurement for the strike plate on the door frame you need the horizontal measurement of where to place it on the door frame. So, on the door, measure the distance from the door edge to the centre of the lock bolt. Transfer this measurement to the door frame and use this to define where the strike plate will go.
  15. Hold the strike plate to the door frame and mark around it.
  16. Use a sharp chisel to excavate the area for the strike plate and also the holes for the lock bolt and latch.
  17. Use provided screws to attach strike plate to internal door frame to complete the job.

This article is provided only as a guide; please follow manufacturers instructions and measure twice, cut once. For your average DIYer we would allow approx 30 mins per door.

  • Information is accurate at time of publishing, however, may be subject to change.
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