Where there is an external door there will be a lock, but the type used will depend on the use that the door is put to, and the level of security that is required. For convenience, many doors have a cylinder night latch fitted and though there are extremely good high specification locks of this type available, where better security is required most households have mortice locks. Without going into too much detail, for most domestic uses there are two types available; the mortice Deadlock show here on the right, and the mortice Sashlock shown below. The deadlock is a key only operated lock, where the sashlock is a key and handle operated variant. For a detailed explanation of these locks, see the section 'Mortice Locks'.
Though the fitting procedure of a mortice lock as outlined in this article can be applied to any domestic mortice deadlock, the required wood bit sizes for different locks may vary. So as not to compromise security by installing a badly fitting lock, it is essential that it is fitted in accordance to the manufactures recommendations in respect of wood bit sizes. In addition to this, I should point out that you should only attempt fitting a mortice lock if you have the required tools and are proficient in using them, as the fitting procedure requires working with accuracy to some tight tolerances.
The positioning of a mortice lock will vary depending of the type of lock being fitted, and in which combination it is being used in relation to other locks. In the case of a mortice sashlock, a comfortable height for the door handles is an obvious consideration, as well as where it would best resist door impact or pressure. The ideal position for both these requirements would be as near as possible to the mid-height of the door without cutting into any of the door joints. Fitting a lock directly in the path of a cross member such as the middle rail for example, would mean cutting out most of the timber that forms that joint, which would result in the weakening of the door, a practice not recommended when adding door security! The positioning of a mortice deadlock is not so easily defined, as it is usually fitted as a secondary device to either a cylinder, or sashlock, but generally speaking, its ideal positioning would be to one third of the door from the top or bottom.
A lock cannot be accurately fitted without pencil and gauge line marks being present on the door, so consider how much of these mark will be seen after the job is complete. Any marks on a new door that is to be painted will disappear, however, marks on a door that is to be varnished or finished in a translucent stain will not. As ever with these things, a little thought beforehand will minimise any later problems, as its just a matter of thinking about the extent to which the lines are drawn in relation to what will, or will not be covered up by the lock and the door furniture.
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