FITTING A MORTISE BOLT
Two mortise bolts (in addition to a night latch) should be fitted to the back door. Ideally, position one bolt 100mm from the top of the door and the other 100mm from the bottom. Try to avoid the tenons which join the door stile to the top and bottom rail if you possibly can. Also, try to keep the bolts away from any glass panels fitted to the door.
Fit one bolt at a time. First wedge the door in an open position so you can work comfortably on both the door and the frame. Mark the bolt position with a marking gauge set to half the thickness of the door. Score a line down the middle of the door edge in the exact position where you intend to fit the bolt.
The next stage is to drill a hole to accommodate the bolt. The hole should normally be 13mm in diameter — check the thickness of the bolt just in case — and deep enough to allow the front plate to be rebated into the door edge. Make sure you keep the drill at right angles to the door edge as you work.
When the hole has been drilled, push the bolt into position and mark around the outside of the front plate with a pencil or trimming knife. Remove the bolt and chisel out a rebate deep enough to set the front plate flush with the door edge. The rebate need not be more than a few millimetres deep. Pare away a thin sliver with the chisel, then insert the bolt and try it for size.
Before screwing the bolt into place, you must drill a hole on the inside of the door only to accommodate the key. Remove the bolt and hold it in position but on the surface of the door, making sure that it is centred above the hole you previously drilled in the door edge. Mark where the keyhole comes on the face of the door then, with a 16mm bit, bore a hole through from the side of the door. Do not drill all the way through — stop as soon as you reach the bolt hole. The bolt body can then be reinserted into the hole and screwed to the door edge.
Next fit the keyhole cover. You will find it easier to position the cover if you push the key through the plate and insert it into the hole while you are drilling and screwing. Then remove the key and lay it to one side.
Now fit the bolt box or bolt cover plate into the door frame. To mark its position, pull out the wedge, shut the door and turn the lock a number of times. When you open the door. You should find that the end of the bolt has made a clear indent on the inside of the frame. At this point drill a 13mm diameter hole in the frame slightly deeper than the bolt box or cover plate.
Push the box into position and mark around the outer edge of the striking plate with a pencil or trimming knife. Remove the box and chisel out a rebate for the striking plate. Once the plate sits flush with the frame, screw it into position. Finally, close the door and test the bolt action. Repeat the procedure to fit the other bolt.