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.
Among the varieties of brackets most used may be mentioned the following. First, those which are fitted upon a flat surface or pilaster, the front and sides being carved, like those used for bookcases and wardrobe doors. The wood for these should be got out, and the back planed, fitted, and toothed. One end should also be squared, the one that is to be the top in the upper brackets and the bottom in the lower. After carving they are fixed by simply glueing or by dowelling. Second, brackets having two of their sides straight and at right angles to each other. These have a very extensive application, and numerous forms are employed. Sometimes they are merely cut in outline, the front being moulded; the whole design fret-cut is preferable. These brackets vary in thickness from 3/8 in. to 2 in., and occasionally upwards; they are used for most articles of furniture, the heavier kinds being sometimes employed partly as a means of support for shelves, etc, and the lighter more usually for ornamental purposes. When cutting out brackets like these, it is most convenient to mark the wood so that each piece will make 2, leaving the further cutting to the fret-cutter. The advantages of this are obvious.
It is necessary to plane over, and thickness, and to square the edges and ends first; this can be more easily done with a square or rectangular piece of wood than with one approximating to the shape of the brackets. When marking, you can see the size necessary to get out the shape by drawing a line from the extremities of the brackets. Let these lines be the diagonal of the rectangle, and mark your work, so that there is sufficient space to get out the outline inside it when setting the edges square with the outside. It is sometimes advisable to make a slight difference from the diagonal mark when the spaces between the top, bottom, and centre of the outline are considerable. Brackets are fixed either by dowels or screws, generally by a combination of both methods. For most purposes dowels of 1/4 in. diameter are sufficient; for the lighter kinds less will do. Consider the most suitable position for them, where the work will afford the best hold, and where they will prevent it from twisting or moving. It is rarely possible to use screws from the front or face, without the work is applied in such a manner that some part is not easily discernible.
They may, however, be sometimes used from the back or inside.
Many excellent designs for fretwork will be found in Bemrose's 'Fret-cutting and Perforated Carving.'