The steel parallelopipeds termed surface-blocks are from two or three inches across to ten or twelve inches, but seldom any larger, through the great consumption of time necessary to make the larger sizes. An ordinary surface-plate has only one or two plane sides; but a surface-block has six planes, and each one must subtend a right angle with each of the four planes adjoining. Such blocks should be made of steel which is forged only sufficiently to condense the particles and to avoid stretching the metal in any direction. The particular method by which they are forged depends on their thicknesses. If the thickness is not to exceed about two inches, a slab may be forged about two inches thick, and amply large enough for four blocks, which are partly or entirely divided into four by means of a planing-machine parting-tool. While forging a piece of this character, it is necessary to provide ample superfluous metal at each end of the slab, or to reduce each end and form a couple of handles or holders, in order that such portions may be gripped with the holding plates to avoid gripping the intended blocks while being planed. A slab thus made is denoted by Fig. 522; such a piece is first planed on both the broad sides while held with the holders, and the two broad sides are thus made plane and parallel to each other. The work is next put with one narrow side or edge in contact with the planing-table, and with the broad sides in a vertical position; these sides are carefully adjusted to a right angle with the table's face, by means of wedges driven between the lower rough edge of the slab and the face of the table, and also by the aid of an el-square. After the work is adjusted and fixed by attaching holding plates to the holders as before, the upper side is planed, and is thus made square with the two broad sides; the slab is next put upside-down, and the opposite edge is also made square to the broad sides, by which time four of the slab's sides are flattened. The dimensions of the four intended surface-blocks are next marked on one of the broad sides, by scribing very thin lines on the surface, and exactly at right angles to the two planed edges; the slab is then ready to be again fixed for being divided into four pieces, and at this fixing the work is carefully adjusted by the lines so that the cuts shall produce the required right-angular shape on the blocks. If it is intended to entirely cut the work into distinct pieces, the slab must be put upon parallel packing-blocks, instead of in immediate contact with the planing-table ; but if to be cut only partly through, the slab rests in contact with the table, no packing-blocks being required. When the slab is finally adjusted to the lines, eight fastenings are required, the two holders being then of but little use; two of these fastenings are necessary for each intended block, one fastening at each end; by this means, all the places for the intended cuts are exposed to the parting-tool, and each block is securely held until all are separated from each other. In the Figure 522, the five cuts necessary to produce the four blocks are indicated by the letters C.

Surface-blocks which are eight or ten inches thick are not easily divided with parting-tools ; it is therefore convenient to forge them separate, each block having two holders, as indicated by Fig. 523. If a pair of these blocks are wanted, two are fixed near each other and planed together on the table of the planing-machine; both are reversed and finished at the same time, so that both are of similar shape and dimensions. When a pair of large blocks are to be made of one single piece, they are partly divided with a chisel during forging, to avoid the use of heavy parting-tools. A piece for this purpose, partly divided, is denoted by Fig. 524. The two holders shown are to hold the work while the broad and narrow sides are planed; after which the fastenings are taken from the holders, and the two intended blocks are carefully lined to indicate their dimensions ; when thus prepared, the work is again fixed by the lines, and each block is held with plates and bolts while being divided with parting-tools or corner-tools.

Surface-blocks that are not required to be solid may be provided with screwed holes, which greatly facilitate the planing, and also the lathe-turning, when the blocks are prepared with a lathe instead of a planing-machine. The holes in such blocks are bored and screwed entirely through, and cross each other at the centre of each block; such are denoted by Fig. 525, and when so made, they are planed or lathe-turned without any stems for holding being required. Blocks of this sort are held, while planing, with screw-bolts, which are placed through the machine-table near one edge, the screw of the bolt being screwed into the hole of the block. Several blocks may be thus tightly held in a line with each other, and one side of all the blocks planed at one time ; after which, all the blocks are shifted and the fixing bolts are put into other holes, or opposite ends of the same holes, to hold the blocks for planing another side of each block. During these fixings, great care is necessary to fix the planed sides at right angles to the surface of the planing-table; if not, a large quantity of unnecessary finishing after planing will be the result. Such blocks are also easily lathe-turned by bolting three or four to a disc-chuck, and exercising the same care in fixing the turned surfaces to a right angle with the chuck, that was bestowed upon blocks prepared on a planing-machine.