Clamps
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 own material. An early "C" clamp 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".
"C" Clamp
OTHER NAME: "G" clamp
SIZE: Open capacity: 3/4 to 12in.
MATERIAL: Frame; aluminum, malleable iron, pressed steel; Screw: steel
USE: To clamp wood and metal work
The "C" clamp is one of the most versatile and widely used clamps 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 angled work. Pressure is applied either by a thumb screw or a tommy bar. Use blocks of scrap lumber between the clamp and the work to prevent marking.
There is also a version of the "C" clamp which incorporates 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. Final pressure is then applied in the normal way. Hand pressure should be sufficient to tighten any "C" clamp. Extra leverage can either damage the work or distort the frame of the clamp.
Small lightweight aluminum clamps are available for model work. Normally they need only be finger tight but extra pressure can be applied by a wrench or screwdriver.
Long reach clamps
"Long reach" clamps are specifically designed to hold the workpiece some distance from the edge.
Edge clamps
Special "C" clamps are also available to hold edgings onto the end of a workpiece.
They are either regular "C" clamps with one additional screw thread at right angles to the first, or modified with three screw threads which give greater flexibility for positioning the centre screw accurately on the workpiece.
Handscrew
OTHER NAME: Parallel clamps
SIZE: Open capacity: 2 to 12in.
MATERIAL: Jaws: beech, maple, steel; Screws: hornbeam,bsteel
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 a hole while the other end of the screw works in a threaded hole in the other jaw. The rear 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.
Adjusting the handscrew
Grip each handle and rotate the tool either toward or away from you to close or open the jaws. Place the tool on the work and adjust the jaws to fit. Tighten them by adjusting the rear screw.
Protect the jaws from accidental gluing during use with a coating of wax, or place paper or plastic sheeting between the tool and the job.
Handscrews adjust to any angle.
Spring Clamps
SIZE: Open capacity: 1 to 3in.
MATERIAL: Steel
USE: To provide light pressure
Spring clamps are entirely hand operated. The jaws are opened by squeezing the handles together. The clamp 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 marking the work. If the surface is too delicate for such local pressure, spread the load by inserting scraps of hardboard between the clamp and the work.
Pinch Dog
OTHER NAMES: Joint clamp, joiner's dog
SIZE: 1/2 to 3in.
MATERIAL: Steel
USE: To hold boards together while gluing
The two tapered points of the pinch 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 Clamp
SIZE: Jaw capacity: 4 to 39in.
MATERIAL: Jaws: malleable cast iron; Bar screw: steel; Handle: hardwood
USE: To clamp woodwork
The fast action clamp is used in similar circumstances to the "C" clamp.
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 movable 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 movable 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.
Model maker's clamps
These are small solid nylon clamps which work on the fast action principle. Rubber bands apply pressure to the jaws.
Bar Clamp
SIZE: Length: 24 to 60in.; Capacity: 18 to 54in.
MATERIAL: Bar: steel; Clamp head: malleable iron
USE: To hold large boards or frames together while gluing
The bar clamp is a simple rectangular sectioned steel bar, drilled at intervals to take the fixing peg of a cast iron tail slide. 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 is located in the last hole of the bar to prevent the tail slide 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 clamps 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 whef; the pin will automatically locate in the hole. Unlike the loose retaining pin this type of catch cannot fall out as the clamp 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 which locates in the notches and tightens under load.
An extra long clamp can be improvised by bolting two bars together side by side.
Clamp Heads
SIZE: To fit 1in. wooden rail
MATERIAL: Malleable iron
USE: To make up a bar clamp
Clamp heads are used to build a bar clamp to any length. One foot of the clamp is fixed and the other adjusts to locate over a wooden rail of the desired length, 1in. thick and a minimum of 1-1/2in. wide. The clamps are secured by steel pins, which pass through 3/8in. diameter holes drilled through the rail. As the length of the rail increases it may be necessary to increase the width in proportion to keep the clamp sufficiently rigid.
Pipe Clamp
SIZE: Length: as required; Bar: 1/2in. and 3/4in. bore
MATERIAL: Bar: steel; Clamp heads: cast iron
USE: To hold large boards or frames together while gluing
The pipe clamp provides another way to make up a clamp of non-standard length. A 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.
Clamping frames
Position each bar clamp in line with and centreed on the joints. Use softwood biocks to protect the work and to spread the load. Position the tail slide to fit the work, leaving the adjustable shoe enough thread for final adjustment. Glue and assemble the frame. Increase the pressure on the clamps working from one to the other to even up the forces.
When the frame has been fully clamped excess glue may be gradually pressed out from the joints; the clamps may need slight adjustment after a few minutes.
Clamping planks
Bar clamps are used to hold glued planks together when making a wide board. Place the clamps alternately over and under the workpiece to prevent the boards from bowing in either direction.
Preventing distortion
Lightweight bar and pipe clamps can distort under pressure, and mark the surface of the work. To prevent this, either position the work nearer the toe of the jaws or protect the work with scrap hardboard. The edges of the workpiece should also be protected with softwood strips. If one or more boards slips out of line while clamping, place a softwood block over the joint and knock it flush with a mallet.
"T" Bar Clamp
SIZE: Length: 36 to 84in.; Capacity: 30 to 78in.
MATERIAL: Bar: steel; Clamp heads: malleable iron
USE: Heavy duty clamping
The "T" bar clamp is a heavy duty version of the bar clamp. The "T" section
of the bar is designed to resist bending when under pressure.
The clamp heads are machined to fit over the top piece of the section and are proportionally larger than those used on standard bar clamps.
Web Clamp
OTHER NAMES: Strap clamp, band clamp
SIZE: Length: 15ft.; Width: lin.
MATERIAL: Webbing: nylon; Mechanism: steel
USE: To apply even pressure to frames while gluing
The web clamp is used to apply even pressure around 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.
Using the clamp
The clamp is tightened by pulling on the free end of the webbing (1). Additional pressure is applied by tightening a ratchet nut on the mechanism with either a wrench or a screwdriver (2). To loosen the clamp, operate the lever which locks the ratchet and pull on the webbing (3).
Jet Clamp
SIZE: Length: 12in., 24in., 36in and 48in.
MATERIAL: Steel
USE: To clamp wood and metal work
A jet clamp consists of two movable jaws which slide on a plain rectangular sectioned bar to any position to form a clamp 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 thumb screw on one of the jaws. Both the jaws are reversible so that outward pressure can be applied.
Frame Clamp
SIZE: Up to 3ft. square
MATERIAL: Comer blocks: plastic, aluminum; Tension device: steel screws, plastic cord
USE: To clamp a mitred picture frame while gluing
Frame clamps 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 alternately to each joint.
Improvised frame clamp
Protect the corners of the frame with thick cardboard. Cut a length of strong twine twice the circumference of the frame. Double it and tie it around the frame. Insert a piece of dowel between the lengths of twine and turn it to apply tension. Tie off the dowel against the frame until the glue is set.
Mitre Clamp
OTHER NAME: Corner clamp
SIZE: Capacity: 2 to 4-1/2in.
MATERIAL: Aluminum alloy, cast iron USE: To clamp mitreed joints
The mitre clamp 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 angled fence. Some clamps 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 .
After gluing the two halves of the joint, locate them in the clamp together insuring that they meet before pressure is applied to either screw. Gently adjust the pressure alternately to each half" of the joint until it is firmly held in place. The joint can be further strengthened by nailing.
Flooring Clamp
SIZE: To fit a 1 to 3iin. wide joist
MATERIAL: Various
USE: To close up floorboards before nailing them to joists
Flooring clamps are used to make sure that floorboards fit together snugly.
The clamp 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. Improvised flooring clamp
Lay three pairs of wedges evenly along the length of the board. Nail scrap lumber behind the wedges and drive them toward each other.
