A lewis is one of a category of lifting devices used by stonemasons to lift large stones into place with a crane

Crane (machine)

A crane is a type of machine, generally equipped with a hoist, wire ropes or chains, and sheaves, that can be used both to lift and lower materials and to move them horizontally. It uses one or more simple machines to create mechanical advantage and thus move loads beyond the normal capability of...

, chain block, or winch

Winch

A winch is a mechanical device that is used to pull in or let out or otherwise adjust the "tension" of a rope or wire rope . In its simplest form it consists of a spool and attached hand crank. In larger forms, winches stand at the heart of machines as diverse as tow trucks, steam shovels and...

. It is inserted into a specially prepared hole, or seating, in the top of a stone, directly above its centre of mass. It works by applying principles of the lever

Lever

In physics, a lever is a rigid object that is used with an appropriate fulcrum or pivot point to either multiply the mechanical force that can be applied to another object or resistance force , or multiply the distance and speed at which the opposite end of the rigid object travels.This leverage...

 and utilises the weight of the stone to act on the long lever-arms which in turn results in a very high reaction force and friction

Friction

Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of friction:...

 where the short lever-arms make contact with the stone inside the hole and thereby prevents slipping.

A lewis is most useful when it is not possible to lift the stone with chains or slings, because of either the location or shape of the stone, or delicate projections

Corbel

In architecture a corbel is a piece of stone jutting out of a wall to carry any superincumbent weight. A piece of timber projecting in the same way was called a "tassel" or a "bragger". The technique of corbelling, where rows of corbels deeply keyed inside a wall support a projecting wall or...

. E.g., the closing stone in a string course; cylindrical column

Column

A column or pillar in architecture and structural engineering is a vertical structural element that transmits, through compression, the weight of the structure above to other structural elements below. For the purpose of wind or earthquake engineering, columns may be designed to resist lateral forces...

 drums; decorated column capitals

Capital (architecture)

In architecture the capital forms the topmost member of a column . It mediates between the column and the load thrusting down upon it, broadening the area of the column's supporting surface...

; coping

Coping (architecture)

Coping , consists of the capping or covering of a wall.A splayed or wedge coping slopes in a single direction; a saddle coping slopes to either side of a central high point....

 stones in a pediment

Pediment

A pediment is a classical architectural element consisting of the triangular section found above the horizontal structure , typically supported by columns. The gable end of the pediment is surrounded by the cornice moulding...

. Heavy ashlar

Ashlar

Ashlar is prepared stone work of any type of stone. Masonry using such stones laid in parallel courses is known as ashlar masonry, whereas masonry using irregularly shaped stones is known as rubble masonry. Ashlar blocks are rectangular cuboid blocks that are masonry sculpted to have square edges...

 stones are also bedded using a lewis.

The name lewis may come from the Latin

Latin

Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

 levo -avi, -atum meaning to levitate

Levitation

Levitation is the process by which an object is suspended by a physical force against gravity, in a stable position without solid physical contact...

 or just lift(www.perseus.tufts.edu), but the Oxford English Dictionary online says 'origin obscure'. The Romans

Roman Empire

The Roman Empire was the post-Republican period of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean....

 used the lewis. The specially shaped hole that is shaped to fit the device is known as a lewis hole. Lewis holes in the uppermost masonry

Masonry

Masonry is the building of structures from individual units laid in and bound together by mortar; the term masonry can also refer to the units themselves. The common materials of masonry construction are brick, stone, marble, granite, travertine, limestone; concrete block, glass block, stucco, and...

 coursings are neatly repaired with matching indented plugs after the stone has been set in place.

Safety

Occupational safety and health

Occupational safety and health is a cross-disciplinary area concerned with protecting the safety, health and welfare of people engaged in work or employment. The goal of all occupational safety and health programs is to foster a safe work environment...

 caution: The lewis is liable to slip out of the seating if some of the weight of the stone is subtracted from the appliance, such as when the stone bumps on the scaffolding

Scaffolding

Scaffolding is a temporary structure used to support people and material in the construction or repair of buildings and other large structures. It is usually a modular system of metal pipes or tubes, although it can be from other materials...

 on its way up to its final location. For this reason, a safety sling should always be used together with the lewis until the stone is reasonably close to its final position. Lifting the stone a small distance from the ground before hoisting is the best way to test a lewis. Any sign of looseness or damage should be put right by adjusting the lewis hole or packing the lewis with metal shims.

Bedding a stone using a lewis: The stone is placed on dunnage

Dunnage

Dunnage is a term with a variety or related meanings. Typically dunnage is inexpensive or waste material used to protect and load securing cargo during transportation...

 laid flat with enough clearance for a mortar

Mortar (masonry)

Mortar is a workable paste used to bind construction blocks together and fill the gaps between them. The blocks may be stone, brick, cinder blocks, etc. Mortar becomes hard when it sets, resulting in a rigid aggregate structure. Modern mortars are typically made from a mixture of sand, a binder...

 bed to be placed beneath it. The safety straps are removed, the stone is lifted using the lewis alone, and the dunnage removed with fingers clear. The stone is then lowered onto the mortar bed, and positioned with sharp taps from a rubber mallet

Mallet

A mallet is a kind of hammer, usually of rubber,or sometimes wood smaller than a maul or beetle and usually with a relatively large head.-Tools:Tool mallets come in different types, the most common of which are:...

.

There are a number of different types of lewis used in the stonemasonry trade:

Chain-linked lewis

A chain-linked lewis or chain lewis is made from two curved steel legs, linked by three steel rings. The legs fit into a seating cut in the top of the stone, above the centre of mass. When the top of the curved legs are pulled together by the rings, the bottom portions are forced into the lower part of the seating, thereby providing enough friction to lift the stone.

Split-pin lewis

The split-pin lewis is similar to the chain-linked lewis in that it uses a scissor-like action to produce friction against the inside of the lewis hole. The two legs, semicircular in section, lie side-by-side, and fit inside a 32 mm diameter hole drilled to a minimum depth of 82 mm. This type of lewis seating is the simplest to prepare, requiring a single drilled hole.

Two-pinned lewis

A two-pinned lewis consists of two 13 mm diameter steel pins, linked by a short chain. The pins are inserted into opposing holes that are drilled into the top of the stone at about 15° from vertical, and at least 75 mm deep. It operates by gripping the stone (like two fingers lifting a tenpin bowling ball) as the weight of the stone is taken up by a crane or winch. The advantage of using this type of lewis is that it is simple to prepare—two angled drill holes are all that is necessary. Like other types of lewis, it is susceptible to pulling out as the stone is lifted. It should always be tested before hoisting, and used in conjunction with safety slings.

Three-legged lewis

A three-legged lewis, also known as a dovetailed lewis, St Peter's keys, or a Wilson bolt fits into a dovetailed seating in the top of a building stone. It is made from three pieces of rectangular-section 13 mm-thick steel (legs) held together with a shackle, allowing connection to a lifting hook. The middle leg is square throughout its length. The outer legs are thinner at the top, flaring towards the bottom. Held together, the three legs form a dovetail shape. The lewis hole seating is undercut (similar to a chain-linked lewis hole) to match its profile.

The first outer leg is inserted into the lewis hole, followed by the second outer leg. The inner (parallel) leg is inserted last, pushing the outer legs into contact with the inside of the lewis hole. The shackle is unbolted, placed over the legs, and the bolt fastened through both the shackle eyes and the eye in the top of each leg.

This type of lewis is the safest to use because it relies on its dovetailed shape for security instead of friction alone, however the seating is time-consuming to prepare.

Their resemblance, once assembled, to a bunch of keys gave rise to an alternative name for them of "St Peter's keys". This has frequently been represented allegorically, drawing the name of "St Peter" as "the Rock on which I shall found my Church" into an allegory between the fabric of a church building and the community of the church itself. Some illustrations of St Peter even show him carrying a bunch of keys which appear to have no wards. These aren't keys in the lock-making sense, but in this sense of stonemasonry.

External lewis

The external lewis, kerb lifter or slab lifter is a type of lifting device used in the stonemasonry

Stonemasonry

The craft of stonemasonry has existed since the dawn of civilization - creating buildings, structures, and sculpture using stone from the earth. These materials have been used to construct many of the long-lasting, ancient monuments, artifacts, cathedrals, and cities in a wide variety of cultures...

 trade since Medieval times. The external lewis was originally shaped like a pair of scissor-tongs

Tongs

Tongs are used for gripping and lifting tools, of which there are many forms adapted to their specific use. Some are merely large pincers or nippers, but the greatest number fall into three classes:...

, and swung from a treadwheel

Treadwheel

A treadwheel is a form of animal engine typically powered by humans. It may resemble a water wheel in appearance, and can be worked either by a human treading paddles set into its circumference , or by a human or animal standing inside it .Uses of treadwheels included raising water, to power...

 crane.

The external lewis has been modified to handle kerbstones and large slabs of polished stone in contemporary stone yards.

A manual kerb lifter is a large, adjustable pair of tongs, made with a pair of handles so that two men can manoeuvre heavy blocks of stone into position. A mechanical kerb lifter can also be made to fit mechanical lifters like forklifts or crane-trucks so that larger stones can be placed.

In stone yards, a slab lifter is hung from a shed gantry or forklift to transport slabs of stone between storage racks and stone processing machines. It consists of two hinged, weighted friction pads that close astride the top of a slab, and are pulled tightly together by the weight of the slab itself.

The slab lifter uses two safety devices. Safety chains and a support bracket allow safe lifting of large slabs. This lifting appliance also has a safety locking device that is engaged when the gripping pads are activated by the weight of the stone. This prevents any jerking movement from releasing the stone. It is easily disengaged once the slab is secured at its destination.

External links

• The Postgraduate Forum Ted Morgan investigates connections between ancient Roman technology and recent British engineering practices.