In addition to mortice locks fitted to the front and back entrance doors, it is advisable that additional bolts are fitted to these doors. These can either be Tower bolts, the type which are surface mounted, or 'Rack Bolts', or Mortice Bolts. As the name suggests, mortice bolts are similar to mortice locks in as much as they are fitted into the door rather than onto it.
Though not particularly difficult to fit, it is important that all measurements are accurate because in addition to the hole required to receive the bolt, two other holes are required, one into the inside face of the door as the keyhole, and a second into the door frame which will receive and hold the bolt when the door is closed, and if all three are not accurately positioned the bolt will not work.
The reason why these bolts are important is that they compensate for the fact that there is no locking device at these points, and the door if pushed hard enough at either the top or bottom would provide a gap wide enough for a crowbar to be inserted.
The ideal position for the top bolt would be about 150mm from the top of the door, and the other about 200mm from the bottom so as to avoid the door joints (tenons).
The first step in fitting is to mark the position of the upper bolt onto the door edge, which is approximately 150mm down from the top, and using a square, draw a short horizontal line at this point.Then, using a marking gauge, which has been set to half the thickness of the door, score a vertical line crossing through the horizontal mark as shown in 'fig 2'. The door is now marked with the centre position where the bolt hole will be bored to receive the bolt body.
From this mark, use a square to transfer this position to the face of the door, and draw a second horizontal line at the approximate position of where the keyhole will be, also shown in fig 2.
The next stage is to bore the hole to accommodate the bolt at the position where the two lines cross on the door edge. This hole would normally be 16mm in diameter, (though this size could differ between manufacturers) and deep enough to allow the bolt and front plate to be recessed. While drilling, ensure that the drill is always held at 'right angles' both vertically and horizontally to the door.
When the hole for the body of the bolt has been bored out, the next step is to bore a second hole into the inside face of the door for the keyhole. To do this, first measure the distance from the faceplate of the bolt to the centre of the keyhole, and using a combination square or marking gauge, draw a vertical line at this distance from the edge of the door, so that it crosses the horizontal line drawn previously on the inside face.
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