The term working press is entirely my own invention. I use it to describe the device I used to hold my books upright, on fore, spine, head or tail edges. It served me as a sawing and gluing clamp, a cutting press, and a backing press, as well as holding the book for headband sewing and spine decoration. It was long enough to rest on the inexpensive plastic boxes I use for laundry. I even used it as a book press for very small volumes, if my main book press was otherwise occupied.
The basic overall shape of a working press is two long pieces of wood pulled together with threaded rods at either end. The easiest and cheapest way to construct it is to glue up several narrow planks together to make a thicker piece. The face plates are then lined with hardboard for smoothness.
The crucial trait of a working press is that the cheeks must be level. My original working press (assembled in a hurry to use with a new plough) was uneven, and I regret not having taken the time to do it right. It led to bad binding work. My second attempt was better, but still not perfect: the tongue was too narrow for my plough, making it wobble when cutting pages.
In the end, I had the money available to buy a professionally made press for my precision work. I still use the original threaded rod press for some operations (everything but backing and trimming, which require perfectly level cheeks). But my handmade presses, though not good enough for skilled work, were ideal inexpensive "starter" presses, for deciding if bookbinding is an obsession or a whim.
Turned one way up, the press fits with the plough used to trim the pages of a book.
The other way up, it has level surfaces to permit sawing, backing, and finishing operations.
Hole placement is the most important step in the construction of this press. The holes should be centered between the top and bottom edges of the press, so that the grip is even no matter which side is being used. More importantly, they must be in exactly the same place, so that when the threaded rods are in place the two cheeks line up precisely. (This also requires that the two cheeks be exactly the same height, an effect best achieved by using cuts from the same board for making them.) The best way to line the holes up (iff you don't have a drill press) is to clamp the two pieces firmly together, perfectly lined up, and drill both holes at once.
Use the grain pattern on your boards to your advantage - it should run the same way on all the boards, so that if they warp, they will still cup each other and grip the book.
If you're planning to use it with a plough, the press construction will depend on the nature of your plough. Some ploughs have a tongue protruding from the bottom, and want to ride in a groove. Others (like mine) have a groove and look to the press for the tongue. If you layer several pieces of board together, you can create the tongue or groove by layering in a taller or shorter plank.
The planks can be glued together, or glued and screwed. If you glue and screw, do it in before you fit the hardboard. Countersink the screws so they are flush with the surface, and make sure they go from the inside toward the outside. Then you can glue the hardboard over the exposed heads.
Many operations with the working press require the book to be centered in the press, so the grip is even on the book. I have ruled out lines on both sides of the press to allow easier centering, and find this tiny touch to be extremely useful.
These are the types of working press that I have tried or considered: