The slots and square holes in a portable table may often be conveniently used for holding the square stems of rounding tools, bending tools, and other shaping implements represented in Plates 20 and 21; instead of placing the stems into the square holes of ordinary anvils. In Plate 21, two bending tools for bending ends of bars, as shown by Figs. 218 and 219. The number of slits or narrow gaps in each tool may be three or four, if the tools are large enough; and the angles of the gaps with the faces of the tools differ according to the desired angle of the work when angled. For the convenience of shaping curved work, the entrances of the gaps may be curved, as in Fig. 219.

Plate 21

When such a tool is in use, it is fixed by its stem in some convenient hole, and the bar to be angled is heated to a proper softness and upset, if necessary, to obtain a thick portion at the intended corner; after this, the iron or steel is again heated and angled by placing the end of the bar into the gap, to such a distance that the middle of the heated portion shall be in contact with the bearing or projecting edge at the mouth of the gap. When the work is thus fixed, it is ready for angling, which is effected by one or two men pulling down the end of the bar until it is brought to the desired position. After being thus roughly bent, the work is properly shaped by hammering and flattening that part of the iron which is on the angling block.

The angling block shown by Fig. 219 is useful for shaping work which is to be very strong at the corner, having a curve inside and an angle outside. To make such a corner, the iron is heated to welding and driven into the gap with flatters or set hammers.

Gap-blocks for angling and corner-making are made by first preparing a solid block having a square stem, but no gap. The material used may be either Bessemer metal or inferior homogeneous iron ; and the cutting of the gap is performed while cold. For this purpose, the place of the required gap or gaps is marked upon the face and two sides of the block, by means of a scriber and straight-edge; after which the opening is made with drilling about half way through from two opposite sides of the block, and not with drilling from the face of the block. After being drilled with drills of proper sizes, the gap is completed with chiselling and filing.

Large gaps, two or three inches wide, and six or eight inches in length or depth, are formed at the time of casting; the wood patterns being shaped to draw easily from the sand in a direction which is parallel to the length of the gap, and not in a, direction which is at right angles to the block face; consequently the block is cast with one side at the bottom of the mould, instead of the block-face being in that situation.

Gap blocks or other implements of similar character, having wide gaps, are made to suit thin bars, by putting packing plates of various thicknesses into the gaps by the side of the work to be angled.

Screw-Clamps (Fig. 220). - Screw-clamps are used to fix two or more bars or plates together, or to a block or table ; the object being to tightly fasten the pieces in any required relative position during a short time while marking with a scriber or other instrument. Clamps are used also for lifting heavy plates, and for attaching various pieces of work to each other. Screw-clamps are made of all sizes from half a pound weight to fifty pounds; and the form is nearly the same for all dimensions, being similar to that shown in Fig. 220.

When clamps are used for fixing a long straight-edge upon a piece of work, two or three clamps are necessary, and are placed in two or three places along the sides of the straight-edge and the work while in their required positions ; pieces of soft iron are then put upon the straightedge to receive the points of the clamp-screws, and all the screws are tightened with a tommy, by which the straight-edge is securely fixed. During the final fixing, the work is adjusted to its exact intended relative position by giving a few knocks to either the straight-edge or the work to which the straight-edge is fastened, using a tin hammer for this purpose, or, for some work, a copper drift.

For lifting purposes one clamp is often dangerously used, the clamp being suspended with the chain-hook, and the bar or plate which is being lifted being wholly dependent on the bite of the screw-point to prevent the work falling and doing mischief; consequently, for safety, the clamp-screw point should be screwed into the metal sufficient to make an indentation about a sixteenth deep.

A good clamp is that which presents a large bearing surface to the work after being fixed, thus preventing the clamp and work from altering their relative positions. With this object a clamp should be made so that its two arms are nearer to each other at the extremities than at a few inches towards the bottom of the gap, or mouth, as it is termed. Such a clamp, when in ordinary use with the work between, should be screwed tight until both arms are parallel to each other; any further screwing after this will further separate the arms and tend to make the work less secure. During a long usage, the arms of clamps become too wide apart by the frequent screwing; a clamp in this condition should be rectified by heating the thick curved part, and closing the arms to a proper distance.

The metal for clamps should be Bessemer iron or steel; the screw-points also must be of steel, that they may be forced into the work or packing which is being fixed, when such a bite is necessary. These packing-pieces should be hollow at those sides that are to be next the work to be fixed; and the bearing of the clamp also, shown in the Figure by B, should be hollowed by filing a shallow narrow groove along the middle.

The forging of a clamp, when small, consists in making it of one straight piece, which is reduced to a suitable thinness at each end, and the boss for the screw also made at one end, both operations being completed previous to bending the clamp at the middle. Large clamps are conveniently made of two pieces when bending tools are not accessible ; in this case, the joint is made at the thick curved part.