A Centre

A middle point. A centre is also any important place in an object, whether in the middle or elsewhere. The centre of magnitude or extension in or belonging to any object is a point which is at a mean distance from the object's pourtour, or entire external surface. The centre of mean diameters, or axial centre, in or belonging to any body, is the point of intersection of the mean major axis with the mean minor axis; consequently, in a crank-shaft lever, which is forty inches in extreme length, the axial centre is twenty inches from either extreme end, although one of the lever-bosses is much larger than the other. To centre, is to find and indicate the middle points in various sides of pieces that need such processes. Lathe centres are cones, or conical pivots, on which an axle rotates while being turned.

To Chase

To make a screw with a hand-tool upon a piece of work while it rotates in a lathe.

To Chip

To cut with a chisel in two hands. Also to cut with a chisel in one hand while the chisel is driven with a hammer in the other hand.

To Chuck

To chuck a piece of work is to fix it tight upon a chuck ; these chucks are tables, plates, or boxes to which the work is bolted, or fastened by cement. Chucks are of many sizes and shapes, and belong to lathes, planing-machines, drilling-machines, slotting-machines, and others.

A Clamp

A plate or other instrument which grips and tightly holds one piece of work to another, or to a table or platten. To clamp is to fix something with a clamp.

A Clearance

An amount of space allowed between the extremity of a piston's travel and the cylinder-lid. Also the space between a bolt and the boundary of the hole in which the bolt is placed.

To Cog

To cog a wheel is to put teeth into it, which are named cogs. A cog-wheel may be one having teeth solid with the wheel, or one having distinct teeth that are made of wood and fixed to their places.

A Collar

The collar of a bolt, bar, or axle is a ring of metal that may either be slidden loosely along the axle or forged solid with it. Collars are usually circular; but some are square, hexagonal, octagonal, and oval.

To Cone

To cone a pin, or rod, is to make a frustum in some part of the rod; to cone a hole is to make the boundary of a hole to the form of a frustum, or cone, by means of boring tools or punching tools.

A Cotter

A key having pin-holes at the small end for holding a split key.

A Coupling

A joining together of two articles so that they may be easily separated. A coupling for joining two shafts end to end consists of a thick tube, or socket, that fits a few inches of both the shaft-ends that are to adjoin ; and when the two shaft-ends are put into the coupling, both shafts are in one straight line. A preferable mode of coupling consists in using flange-couplings. A flange-coupling is a thick socket, having a broad flange at right angles to the length of the hole for the shaft; around the flange are a few holes for connecting bolts, which are put in and out when coupling and uncoupling is necessary. Two of these couplings are keyed to the two shaft-ends, so that both the flanges are outwards; and when the two faces of the flanges are put together, the bolts are put in and fastened, and the coupling is effected.

A Cover

A cylinder-lid is a cover for one end of a cylinder. A lid of a slide-jacket is a cover for the face to which the lid is bolted.

A Crank, Or Crankle

A crankle is the bent or zig-zag part of a rod or bar. An engine crank consists of only one lever when it is situated at one end of an axle, and includes two levers and the crank-pin when the crank is near the middle of an axle.

A Diagram

A figure or writing on a surface. Diagrams for workmen consist of figures on paper, and also of figures of chalk on boards, sheet iron, and tables. An inscription made with a steel point into a table is also named a diagram.

A Diameter

A distance across or through an object, whether it be the length of the object, or the width of it, or its thickness. The three terms, diameter, axis, and thickness, are synonymous, if not specially defined.

Dies

Dies are moulds of various forms for shaping forgings and other work, and are made of chilled cast iron or of steel Dies for making screws on bolts consist of hard steel grips having inside screws on the gripping sufaces that are to bite the portion of the bolt to be screwed.

A Draught

The draught of a piston-rod key-way is a space which allows the end of the rod to be drawn to its place while the key is being driven into the key-way. The draught of a crank-pin cone is the distance which the extremity of the cone projects beyond the place it will occupy after being heated and fixed.

A Drum

An instrument resembling a cylinder, or, in some cases, a disc. A wheel having a broad rim, which is used for transmitting motion with bands. Drums are fastened to long shafts, and also to short axles, of lathes and other machines; and one drum is sometimes made with a rim broad enough for several bands.

An Edge

The outer extremity of a ridge, whether the edge is thick or thin. That projecting part of a surface which is formed at the junction of two planes that are inclined to each other; or of two curved surfaces inclined to each other. An edge is also a relative term to denote a small side of an object. The edge of a disk is its rim, or one of its boundaries.

An End

The end of a rod is a portion near its extremity. Frequently, for convenience of reference, a rod is said to consist of three parts, or lengths, one length being the mid portion and the two others are the ends. Short rods and levers consist of two equal lengths, termed ends, each end being half the total length of the lever.

An Eye

The eye of a hammer is the hole for the handle. The eye of a boss is the hole for containing the end or some other part of the pin belonging to the boss. An eye-bolt is one having a loop at one end, or having the end punched to make a hole for a pin. Consequently, all such eyes are holes in sockets and rings of various shapes. The shaft-eye of a crank-lever is the shaft-hole.