Crampsclamps and crampingclamping devices

Figure 124A illustrates the usual pattern G-cramp with swivel shoe which adapts itself to the contour of the wood, 124B the Record spin-grip G-cramp which can be adjusted with one hand only, and is an excellent improvement on the older type which required two hands to locate and tighten it, and 124C the Record deep-throat

124 Types of cramp/clamp

124 Types of cramp/clamp

Light pattern G-cramp/C-clamp

Light pattern G-cramp/C-clamp

Spin-grip G-cramp
Heavy pattern T-bar sash-cramp

Deacon patent tail slide

G-cramp. Light bar sash-cramps and lengthening bars are shown in 124D, and the heavy pattern T-bar in 124E, while 124F is the Deacon patent tail slide, which again is a considerable improvement over the old-type loose shoe and pin. The light bar-cramps with either lA in (6 mm) or 5/i6 in (8 mm) bar section are usually considered to be sufficient for normal cabinet-work, and the heavy T-bar for joiner's work, although lengths over 5 ft (1.5 m) are always T-bar section. In choosing the right cramp for the type of assembly a compromise must be effected between weight and stiffness. Light pattern cramps are inclined to pull the bars hollow if the strain is great, while heavy cramps may exert too great a pressure, or with their own weight pull a delicate carcass or twist framing. All cramping must, therefore, be done on a firm and level base, and the completed assembly carefully checked from every angle to ensure that there is no distortion of any kind.

125 Cramping/clamping devices: special cramps Special cramps/clamps

Band-cramps are used in shaped work and have a flexible steel band which conforms to the contours. Figure 125:1 shows a simple version. Figure 125:3 is the corner cramping device for mitred frames, etc., simply made out of four hardwood blocks (125:3 A) threaded on a length of blind-cord and tightened with a stick; the cramping pressure is positive and considerable. Folding-wedges are shown in 125:4 and an improved version of the old wooden hand-screw in 125:2. The old type has beech jaws and hornbeam screws, but the new version has metal screws through pivoted centres, and localized pressure can be applied with the tips of the chops as far inward as the chops will reach, according to the size of the cramp. This type of cramp is particularly useful for laying blisters in veneered work, and for all gluing operations away from the edge which the standard G-cramp will not reach. It is axiomatic that no workshop ever has enough cramps of the right

kind at any given time, therefore the provision of cramping devices should be as generous as possible. Downward pressures can also be obtained with old scale weights up to 56 lb (25.4 kg), sometimes procurable at scrap prices from local dealers' yards; while a concrete brick is reasonably flat, square and weighs about 5 lb (2.26 kg), thus a fair pressure can be built up with a small pile of bricks.

In all cramping/clamping operations the working surface must be protected by padding the cramp jaws with blocks of thin wood, folded newspaper or pieces of felt or rubber, for even a lightly applied G-cramp can leave an indentation in the wood surface which may be difficult to eradicate. Pressures should also be spread with heavy blocks or bearers, particularly in carcass and framed-up work. Metal cramps should be frequently overhauled, the hard glue cleaned off and sash-bars lightly oiled, for there is nothing quite so desperate as a tail slide which refuses to move in the midst of a critical assembly. If resin glues and acid hardeners are used, metal cramps should be isolated from direct contact with the wood surface by scraps of paper, otherwise glue may interact with the steel and deeply stain the wood.

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