Parallels are rectangular blocks of metal, commonly made from

tool steel Tool steel is any of various carbon steels and alloy steels that are particularly well-suited to be made into tools and tooling, including cutting tools, dies, hand tools, knives, and others. Their suitability comes from their distinctive h ...

, stainless steel or

cast iron Cast iron is a class of iron– carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its color when fractured: white cast iron has carbide impu ...

, which have 2, 4 or 6 faces ground or lapped to a precise surface finish. They are used when machining with a

mill Mill may refer to: Science and technology * * Mill (grinding) * Milling (machining) * Millwork * Textile manufacturing, Textile mill * Steel mill, a factory for the manufacture of steel * List of types of mill * Mill, the arithmetic unit of the A ...

drill A drill is a tool used for making round holes or driving fasteners. It is fitted with a bit, either a drill or driver chuck. Hand-operated types are dramatically decreasing in popularity and cordless battery-powered ones proliferating due to ...

or any other machining operation that requires work to be held in a

vise A vise or vice (British English) is a mechanical apparatus used to secure an object to allow work to be performed on it. Vises have two parallel jaws, one fixed and the other movable, threaded in and out by a screw and lever. A vise grip is ...

or with

clamps Clamp may refer to: Tools and devices *Brick clamp, an early method of baking bricks *Clamp (tool), a device or tool used to hold objects in a fixed relative position (many types listed) **C-clamp **C-clamp (stagecraft) ** Riser clamp, a device ...

- to keep work parallel or raised evenly such as in a milling vise to give adequate height for the cutting tool/spindle to pass over.

Description

Parallels come in pairs of two, which are machined to be the same dimensions as their corresponding faces. They come in a variety of thicknesses and size, allowing them to be stacked up or to support a workpiece which doesn't have a flat profile. Parallels commonly have a series of holes drilled on the 'front' face - allowing them to be used to position a

workpiece A workpiece is a piece, often made of a single material, that is being processed into another desired shape (such as building blocks). The workpiece is usually a piece of relatively rigid material such as wood, metal, plastic, or stone. After a ...

or secured using t-slot clamps, and a

countersink A countersink (symbol: ⌵) is a conical hole cut into a manufactured object, or the cutter used to cut such a hole. A common use is to allow the head of a countersunk bolt, screw or rivet, when placed in the hole, to sit flush with or below the ...

on each side to remove any sharp edges. Generally, workshop parallels have 4 faces that are machined and ground - the front, back and sides, although some do have the ends with a smooth surface. The surface of a parallel can often tell how it was manufactured, with a 'grain' showing that it was ground - and a smooth or mirrored finish showing it has been lapped. Parallels that have a good surface tolerance can be lightly bonded together by sliding or rotating two parallels together, and the smooth surfaces allows a temporary molecular-attraction to take place - this is known as Wringing and is also found with

gauge blocks Gauge blocks (also known as gage blocks, Johansson gauges, slip gauges, or Jo blocks) are a system for producing precision lengths. The individual gauge block is a metal or ceramic block that has been precision ground and lapped to a specific ...

Manufacturing

There are two main grades of surface tolerance:Engineering Parallels - Metric/Imperial Units (BS 906-1,906-2) * Grade A - Used for close-tolerance work, such as inspection or precision machining * Grade B - Lower surface tolerances, and are used for lower-precision machining Parallels are first machined to rough dimensions, leaving a few millimeters to allow the rest to be ground. Parallels that only have 2 or 4 precision faces will often have the tool-marks from the machining on the non-ground sides. They are then paired and placed in a grinding machine, and each face is ground until the overall dimensions are correct - they are paired during this stage so that even if the dimensions are not correct, they are still parallel to each other. Then, the individual finishes are applied, from drilling to machining a chamfer along the edges to remove any burrs or sharpened edges. They may also be lapped to achieve a mirror smooth surface. Most parallels are also hardened.. Parallels are manufactured to either

imperial Imperial is that which relates to an empire, emperor, or imperialism. Imperial or The Imperial may also refer to: Places United States * Imperial, California * Imperial, Missouri * Imperial, Nebraska * Imperial, Pennsylvania * Imperial, Texas ...

metric Metric or metrical may refer to: * Metric system, an internationally adopted decimal system of measurement * An adjective indicating relation to measurement in general, or a noun describing a specific type of measurement Mathematics In mathem ...

dimensions, and are often sold in a set, with several pairs of different sizes.

Uses

Parallels are used in machining operations, be it

milling Milling may refer to: * Milling (minting), forming narrow ridges around the edge of a coin * Milling (grinding), breaking solid materials into smaller pieces by grinding, crushing, or cutting in a mill * Milling (machining), a process of using rota ...

ing,

turning Turning is a machining process in which a cutting tool, typically a non-rotary tool bit, describes a helix toolpath by moving more or less linearly while the workpiece rotates. Usually the term "turning" is reserved for the generation ...

or sometimes grinding. The most common use is to support work when it is in a vise or clamped to the machine bed. If a workpiece is too small to be machined in a vise without it being in contact with all three faces of the vice - parallels can be used either side to give clearance from the vise, and to give support from underneath to eliminate the workpiece being pushed down by the force of the cutting tool. Parallels of different sizes can be used to support a workpiece that doesn't have a 'flat' surface underneath, or to give clearance when drilling in a vise to stop the drill damaging the vise. Parallels can also be used if the vise itself has a damaged face, which could cause the workpiece to be held insecurely. Other uses include giving a raised surface when using t-slot clamps and for comparison with a surface or machined face to check the flatness. Image:Parralles in vise.JPG, Parallels to raise workpiece Image:Parralles stacked vise.JPG, Parallels with uneven workpiece

Notes

{{reflist Metalworking tools Metalworking measuring instruments

Description

Manufacturing

Uses

See also

Notes