Metal devices using screws for holding or clamping small workpieces were first used by locksmiths in the late Middle Ages. When suitable taps and screw boxes became available in the seventeenth century, the metal clamps were taken over by woodworkers, especially carpenters, using their material. An early “G” cramp in metal is shown in Bergeron(1816), but further development only became possible when machine-cut square threads replaced the “V” thread of the wooden screws.
Handscrews were a portable version of the double screw wooden bench vise with parallel jaws. The modern pattern seems to have been an English brainwave. It is rarely found in foreign workshops or tool lists, although one Russian textbook shows an example, describing it as “heavy and rather clumsy in use”.
Size: open capacity- 20mm to 300mm
Material: frame- aluminum, malleable iron, pressed steel, ,screw- steel
Use: To cramp wood and metalwork
The "G" cramp is one of the most versatile and widely used cramps in both wood and metal workshops. The shoe is attached to the end of the screw thread by a ball joint which enables it to adapt to the angled work. Pressure is applied either by a thumbscrew or a tommy bar. Use blocks of scrap timber between the cramp and the work to prevent marking.
There is also a version of the "G" cramp which incorporated a knurled wheel around the screw thread, allowing the tool to be spun finger tight with the finger and thumb of one hand while the other hand holds the work. The final pressure is then applied in the normal way. Hand pressure should be sufficient to tighten any "G" cramp. Extra leverage can either damage the work or distort the frame of the cramp.
Small lightweight aluminum cramps are available for model work. Normally they need only be finger tight but extra pressure can be applied by a spanner or screwdriver.
Size: open capacity- 50mm to 300mm
Material: jaws-beech, maple, steel, , screws- hornbeam, steel
Use: To clamp angled work
Wooden handscrews have been used for many years in woodworking shops. Earlier designs have two wooden screws to adjust the jaws. The handle end of the forward screw runs freely in the hole while the other end of the screw follows the same arrangement, but the other way around.
Modern handscrews are fitted with metal threaded spindles in place of a threaded hole, in the jaw itself. These rotate freely in the jaw, to accommodate angled work. The screws are also metal and the direction of thread reverses halfway along the rod so that each jaw can be advanced or retracted at the same time.
Size: open capacity- 25mm to 75mm
Use: To provide light pressure while gluing
Spring cramps are entirely hand-operated. The jaws are opened by squeezing the handles together. The cramp is positioned on the work and the handles released.
The jaws may be shaped to clamp on round stock as well as flat areas. On some models, the jaws are dipped in plastic to prevent them from marking the work. If the surface is too delicate for such local pressure, spread the load by inserting scraps of hardboard between the cramp and the work.
Size: 10mm to 75mm
Use: To hold boards together while gluing
The two tapered points of the joiners dog straddle the joint between two boards being glued together, As the dog is driven into the end grain it automatically pulls the boards tightly together. For a tight glue line along the entire length of the board, make sure that the two halves of the joint are completely flat.
Fast Action Cramp
Size: jaw- (100mm to 1000mm),
Material: jaws- (malleable cast iron), bar /screw- (steel), handle- (hardwood)
Use: To clamp woodwork
The fast action cramp is used in similar circumstances to the "G" cramp. The jaw holding the adjusting screw is free to move on the normal rectangular sectioned steel bar. The fixed jaw is fastened to the work and the moveable jaw is slid along the bar until the ball-jointed shoe also comes into contact with the work. The handle is then turned, automatically locking the moveable jaw in place as pressure is applied.
Some fast-action clamps are supplied with nylon jaw covers to protect the work. Alternatively, you can use softwood blocks in the normal way.
Fast Action Cramp
Size: length- (600mm to 1500mm), capacity- (460mm to 1370mm)
Material: bar- (steel), cramp head- (malleable iron)
Use: To hold large boards or frames together while gluing
The bar cramp is a simple rectangular sectioned steel bar, drilled at intervals to take the fixing peg of a cast-iron tailslide. The retaining peg, a tapered steel pin attached to the tail slide by a stout length of chain, is inserted in the hole behind the slide to act as a stop.
A nut and bolt are located in the last hole of the bar to prevent the tail slide from falling off. At the other end of the bar is an adjustable jaw which takes up final adjustment by means of a steel screw.
Some bar cramps have tail slides with an integral spring-loaded catch operated by a push-button. With the button depressed, the slide can be adjusted to a new position where the pin will automatically locate in the hole. Unlike the loose retaining pin, this type of catch cannot fall out as the cramp is turned over.
There are also some models which have a bar with notches on the underside instead of holes. The tail slide has a fixed pin that locates in the notches and tightens under load. An extra-long cramp can be improvised by bolting two bars together side by side.
Size: Length- as required, bar (12mm and 19mm)
Material: bar- (steel), cramp heads- (cast iron)
Use: To hold large boards or frames together while gluing
The pipe cramp provides another way to make up a cramp of non-standard length. Black iron or mild steel pipe of convenient size is threaded at one end to take the frame of a screw-adjusted jaw. The sliding jaw runs on the pipe to the required position. It is locked either by a lever-operated cam or a one-way clutch mechanism which operates when the slide is under load.
"T" Bar Cramp
Size: length- (900mm to 2100mm), capacity- (750mm to 2000mm)
Material: bar- (steel), cramp heads- (malleable iron)
Use: heavy-duty cramping
The "T" bar cramp is a heavy-duty version of the bar cramp. The "T" section of the bar is designed to resist bending when under pressure. The cramp heads are machined to fit over the top piece of the section and are proportionally larger than those used on standard bar cramps.
"T" Bar Cramp
Size: length- (4.5m) width- (25mm)
Material: webbing- (nylon), mechanism- (steel)
Use: to apply even pressure to frames while gluing
The web cramp is used to apply even pressure around the square and tapered frames. It is especially useful for making or mending chairs. The loop formed by the webbing is extended to fit around the frame being glued.
Size: length- (300mm, 600mm, 900mm)
Use: to cramp wood and metalwork
A jet cramp consists of two moveable jaws which slide on a plain rectangular sectioned bar to any position to form a cramp of the required length. Both jaws are fitted with swivel brackets on which protective rubber, smooth metal, textured metal or "L" shaped pads can be fitted.
When both jaws are in contact with the work, the slack can be taken up by turning the thumbscrew on one of the jaws. Both the jaws are reversible so that outward pressure can be applied.
Size: up to (900mm square)
Material: corner blocks- (plastic, aluminum), tension device- (steel screws, plastic cord)
Use: to cramp a mitred picture frame while gluing
Frame cramps are usually used in sets of four. Each corner block is held under tension in one of two ways. The simplest form consists of a cord passed around the frame and back through a cleat. The cord is pulled and held in tension by the cleat so that equal pressure is applied to each joint.
In the alternative design, tension is provided by knurled nuts running on threaded rods which pass from block to block. Apply even pressure alternatively to each joint.
Size: capacity (50mm to 115mm)
Material: (aluminum alloy, cast iron)
Use: to cramp mitred joints
The mitre cramp has two screw-adjusted "feet" set at right angles to each other, which will hold the two halves of a mitre joint against a right angles fence. Some cramps incorporate a slot, which bisects the angle; this guides the blade of a tenon saw to cut the parts of the joint accurately to 45 degrees.
After gluing the two halves of the joint, locate them in the cramp together ensuring that they meet before pressure is applied to either screw. Gently adjust the pressure alternatively to each half of the joint until it is firmly held in place. The joint can be further strengthened by nailing.
Size: to fit a 38mm to 90mm wide joist
Use: to close up floorboards before nailing them to joints
Flooring cramps are used to make sure that floorboards fit together snugly. The cramp has spring-loaded cams on the underside which fit over the joist behind the floorboard. The jaw locates over the edge of the board and pressure is applied through beveled gears by turning the tommy bar. As the pressure increases the knurled cams tighten on the joists.
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
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