The bar of this may be any length, but a convenient one will be about 3 ft. The wood should be hard and strong, such as oak or ash, but it is by no means necessary that these only should be used. Stuff about 1 in. down by 3 ins. wide will be suitable, but these dimensions may vary considerably, as all that is wanted is that the cramp shall be strong enough. The lower edge is notched much after the style of an exaggerated saw, or it may simply have a series of half-round holes; anything, in fact, which will allow the iron pin connecting the sliding block to catch. The upper edge to within a few inches of the block in which the screw works has a groove ploughed along it. In this groove a corresponding tongue on the lower edge of the sliding block fits. The block is thus guided in a backwards and forwards movement, but is restrained from working laterally. The sliding block may be about 4 ins. high and perhaps a little wider on the base, and is best with the grain perpendicular. The strain is then not so apt to cause breakage as when the grain is parallel with it. Much, however, depends on the strength of the wood, and size also is of comparatively little importance. To form a connexion between the bar and block as well as a stop to the latter, an iron loop must be formed, the sides being of thin plate, and the stop and pin which runs through the sliding block being round pins, say, 1/8 in. thick. These pins should be shouldered and then rivetted. The hole in the block should be large enough to let the one through it fit easily, and of course the rivetting can only be done after the pin is in. Block and bar should be of the same thickness. The exact shape of the block is a matter of fancy, and does not affect the working of the cramp.
Fig. 42.- Boxes and Taps for Wood-screws.
The screw-block at the other end is a fixture, and it must be well fastened. Unless the maker has a box and tap for wood-screws (Fig. 42) - a somewhat expensive appliance and one not often seen in the cabinet shop - he cannot attempt to make the screws himself, but will probably be able to get a turner to do what is necessary. If he cannot, it may be suggested that a jaw and screw of a hand-screw can easily be adapted. To make a firm fastening, a hollow may be cut on each side of the bar of the width of the block. This has a slot cut in it to fit, and the two pieces may then be secured by two or three screws or wooden pegs. Care must be taken that the block is fitted so that the screw works parallel with the bar, and its height should be such that it is opposite the face of the sliding block. The point of the screw should have a small iron spike fitted into it. This may easily be managed by driving in a screw-nail, of which the head can be filed away and a projecting point, say, 1/8 in. long left. To prevent the wood splitting, a small ferrule of brass tubing like that on a chisel handle should be fastened on before driving in the nail. The end of the wooden screw may be cut to fit the tubing if necessary.
Fig. 43. - Wooden Cramp.
The completed cramp is shown in Fig. 43, and there will be no difficulty in recognising the various parts which are shown separately by Figs. 44 to 48.
Fig. 44. - Bar for Screw block.
Fig. 45 - Screw-block to fit Bar.
Fig. 46 - Bar showing Groove.
Fig. 47. - Sliding - block showing Tongue.
Fig. 48 - Iron Link.
To use the cramp, the sliding - block is placed in about the position required, the loose link allowing it to be moved freely, but forming a stop when necessary.
The wood to be cramped is then placed, and tightened up by turning the screw. To prevent the point injuring the work, place a piece of waste wood between them.
Bruises from the moving block may be prevented in a similar manner.
A rough and ready form of cramp may be made by simply nailing two pieces of wood across a board parallel with each other, and wider apart than the work to be cramped up. This is laid between them and tightened up by means of wedges. This makeshift cramp is shown in Fig. 49, and may come in handy when the regular ones are otherwise engaged.
Fig. 49 - Improvised Cramp.
Fig. 50 - Improvised Cramp.
A similar contrivance is that represented by Fig. 50, which consists merely of four pieces of wood of any convenient size nailed together. The work to be cramped is placed within the opening and tightened up as before with wedges. Other forms of cramping arrangements will no doubt suggest themselves if they become necessary.