What methods were used to allow for adjustable shelves in antique casework?
In most bookcases of the 18th and early 19th century, shelves were fixed to the sides and not adjustable. When adjustable shelves were needed, the most common method was to have repeating dadoes or horizontal cleats. But, with this method, a face frame could not be used because it would hinder the removal of the shelf. I have not seen peg holes for this era furniture, but it would not surprise me if they were rarely used.
An unusual option is to make a sawtooth shelving support system (aka birdsmouth shelf support). I do not know when these were first used for sure (leave me a comment if you know). They are certainly seen on cabinets from the late 19th century. In fact, hand planes to create the sawtooth rack do exist from the late 1800's as seen in a couple of German tool catalogs. A gentleman by the name of Wolfgang Jordan describes another similar plane.
|A No. 20 1/2 Zahnleistenhobel (translated as a Rack Plane) from the 1909 Joh. Weiss & Sohn|
Alvin Sellens, in his Dictionary of American Hand Tools refers to these planes as bookcase planes or shelf rail planes.
Not having found any information on the topic, here are the steps that I came up with to make the sawtooth system by hand.
The key is to work all four pieces together. First dimension the racks and mark them at a consistent interval.
Next, make a series of crosscuts of the same depth at the marks. A saw with a depth stop helps
|Disston No. 14 duplex saw|
After the crosscuts, mark diagonally from the bottom of one cut to the top of the adjacent cut.
At this point, you can clamp all four pieces together and use a large chisel or slick to make the diagonal notches. Alternatively, a miter jack provides more accuracy as shown below.
Once the support brackets are made, cut out the trapezoidal cleat to the exact width needed and you are done.