This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
This is an every-day joint, and apparently one of the simplest, yet it is very often badly made. Each of the pieces has 3 surfaces in contact, viz. the broad face a of Fig. 514, the side d, the front b, corresponding to similar ones on h, to which it is supposed to be necessary to attach it at right angles. As a joint it has no strength however well made; but it is of very frequent use in stuff of all sizes, and is used not only to join a piece at right angles (or at some intermediate, angle) to another, but also to join them length wise. The line of the end b must be accurately scribed with the help of a square, and, with the same appliance, the line answering to c e of h must be marked round 3 sides of each piece. Then with a marking gauge, ef and its counterpart, which, together, determine the plane of a, are set off, and this line is carried along the end g. On white wood, a finely-pointed (or finely-edged) pencil will make a better line. It is here that amateurs are apt to be lazy. They mark perhaps b, saw down a shoulder, with no further guide line, and holding a broad chisel at the end, hit it with a mallet, and off goes the whole cheek piece, leaving possibly a fairly true face, and more generally a very untrue one - so untrue frequently that no subsequent paring will correct it.
But as it will be much concealed from view, it is allowed to pass muster, and a nice botched job it makes. Supposing this intended, as it often is, to be a glued joint, the great object to be aimed at is to make each face as level and true as possible, so as to provide plenty of surface contact. We may, in this way, even make the half-lap joint strong enough. Hence it is essentially necessary to scribe all lines with accuracy, and then to cut precisely up to them. The cutting across the grain will, of course, be done by the tenon saw, which be will carried down to the line gauged to show the line e f marking the position of the half-thickness of the stuff. Then the work should be stood end up in the vice, and the cheek piece carefully removed, leaving the surface, if possible, so flat and true as not to need subsequent dressing with the chisel. A small hand saw will do this best, its teeth set out only just so far as to prevent the blade from binding in the cut. A saw known as a panel saw will do nicely; a large baud saw with much set is far more difficult to use.