The simplest form of back is a sheet of plywood, chipboard or, for a lighter job, hardboard. It can be of any thickness from 3mm upwards, according to the size of the cabinet; but remember that a back is not just a filling and nothing more. The cabinet depends on it for quite a lot of its rigidity. It must, therefore, be of reason-able thickness to prevent racking. Furthermore, its weight is of definite value, especially pieces which have large doors liable to overbalance the cupboard when opened. How such a back generally fits in rebates worked in the ends. Note how the top and bottom are flush with the rebate. Screws are used for fixing, except for small jobs for which nails can be used.
A mun tin back has the advantage of simplicity. It consists of a series of grooved uprights or screwed to the top and bottom with panels between. Fig. 36 shows the idea. Note how the muntins are cut back as far as the groove A so that the panels will be flush. If solid wood is used for them, the nails should be inserted near the center only, not at the sides. The panels will then be free to pull out of their grooves in the event of shrinkage and so not be liable to split. Today, however, plywood or hardboard is generally used. An alternative occasionally used is the solid wood tongued-and-grooved back. Either V or beaded joints should used so that any opening due to shrinkage is not noticeable. Note that a rebate at top and bottom is desirable as it helps to resist side racking once the center screw is inserted.
The most satisfactory back in that it has the greatest rigidity and is free from shrinkage troubles is the paneled type. The whole thing is put together with mortise and tenon joints, the panel fitting in grooves. Normally the panels are the groove width being arranged to suit. Incidentally, if solid panels are fitted a mullet can be used for testing the fit. This mullet is simply an off cut of the rail worked with the same size of groove. When a back has to present a flush appearance inside, thicker panels are used, their edges being tongued-in.
A note applying to all solid wood backs is that, if the job is to be stained, the panel edges or tongues must be stained before fixing. Otherwise, if a panel pulls out of its groove it will show a line of bare wood. The backs of circular or shaped mirrors are invariably cut in a single piece of plywood or even hardboard and screwed on. When the ends of the cabinet are in solid wood it is advisable to work sloping rebates for the back as at E, Fig. 39. There is then less liability for the back edge to curl outwards.
- Old time cornice and frieze in one with the carcase.
- Cornice and frieze made up as a separate unit. In the best work the front corners are miter dovetailed. The molding may be backed with softwood built up in layers pitched or in the solid.
- Simple plywood back screwed into rebates in cabinet ends.
- Simple form of muntin back. It was often used as a cheap alternative to the paneled back.
- Back of tongued-and-grooved boards.
- Rebates for use with solid wood tongued-and-grooved back.
- Framed and paneled are alternative sections. That would require miters to allow for the rounded corners: panel tested for thickness when solid wood is used; it has sloping rebate for back.