To properly prepare students for advanced machine design it has been found necessary to introduce a course designed to apply the principles of mechanical drawing to the solution of practical problems in machine construction and to familiarize the student with the arrangement and proportions of the most important machines and their details recognized by competent engineers to be the best practice of the present time.

It is essential to intelligent study and an economical expenditure of time and labor that, before attempting to design a new machine or improve an old one, the student should post himself with all possible information concerning what has already been done in the same direction.

To this end the present work has been prepared. In it we have attempted to show what is the best United States practice in the design and construction of various machines and details of machines, using rules and formulae whenever feasible in working out practical problems.

In addition to this will be found the latest and most approved drafting-room methods in use in this country, without which most drawings would be practically useless. Up to the present time no text-book that we know of has been published in the United States that could in the best way fill the need as explained above.

Books of a somewhat similar nature have been published in Great Britain, showing that the same need has been felt there as here. These books, modified to suit American practice, have been used to some extent in this country because they were the best to be had, but are not by any means all that can be desired for our purpose in their present form.

While preparing this course for the sophomore students in Sibley College the authors endeavored to secure samples of the actual machines ox parts of machines as collateral in illustrating the exercises given in the book, with a result that in our drafting-rooms we have many examples of modern machine construction placed convenient to the students hands, so that they may examine and handle the actual thing itself while solving the problems in drawing and designing. This we believe of great importance in the study of machine design and construction, because few are able to describe a machine even with the assistance of a drawing so well as to enable the student to conceive it in his mind as it actually is.

The preparation necessary for the proper understanding and execution of the problems contained in this book is as follows: use of instruments, instrumental drawings applied to drawing geometrical problems in pencil and ink, thorough knowledge of the conventional lines, hatch-lining and colors for sections, mechanical and free-hand lettering, orthographic projection in the third angle, isometrical drawing - in brief all that is contained in “A Course in Mechanical Drawing,” by John S. Reid, published by John Wiley & Sons, New York.

In the preparation of the drawings for this work we are indebted to many of the leading engineering firms of this and other States, who have kindly supplied us with drawings and samples of the latest and best practice of the day. Our thanks are especially due to the Dodge Manufacturing Company, the Detroit Screw Works, the Buckeye Engine Co., the United States Metallic Packing Co., the National Tube Works, the Ridgeway Dynamo & Engine Co., the Murray Gun Works, Henry R. Worthington, Robt. Pool & Sons, the Baldwin Locomotive Works, the Schenectady Locomotive Works, the American Pulley Co., the Hyatt Roller Bearing Co., the Macintosh and Seymour Engine Co., and many others.

Our acknowledgments are also due to many of the best authorities on the different subjects treated, among which may be mentioned Thurston's “Materials of Construction”  A. W. Smith's “ Machine Design,” Klein's “Machine Design,” Unwin's “Machine Design,” Barr's “Boilers and Furnaces,” Peabody and Miller's “Steam Boilers,” Low and Bevis's “Drawing and Designing,” John H. Barr's Kinematics,“ Thurston's “Steam Boilers,” Reuleaux's “Constructor,” the “Proceedings of the American Railway Master Mechanics' Association, etc.,

Keys are employed to connect wheels, cranks, cams, etc., to shafting transmitting motion by rotation. They are generally made of wrought iron or steel, and are commonly rectangular, square, or round in cross-section. The form of key in general use is made slightly tapered and fits accurately into the key-way, offering a frictional holding power against the keyed piece moving along the shaft. The groove or part where the key fits on the shaft, and the groove into which it fits on the piece it is holding is called the key-bed, key-way or key-seat. For square or rectangular keys, when the keyed piece is stationary on the shaft, the .bottom of the groove on the shaft is parallel to the axis, while that of the groove in the piece it is securing is deeper at the one end than the other to accommodate the taper of the key.

Keys may be divided into three classes: I. Concave or saddle key; 2. flat key; 3. sunk key.

Saddle Key. This form of key has parallel sides, but is slightly tapered in thickness and is concaved on the underside to suit the shaft, as shown in Fig. 74. As the holding power depends entirely upon the frictional resistance, due to the pressure of the key on the shaft, the saddle key is only adapted for securing pieces subjected to a light strain. When this key is used for securing a piece permanently, the taper is usually made I in 96, but when employed on a piece requiring to be adjusted, such as an eccentric, the taper is increased to I in 64 to allow the key to be more easily loosened.

Flat Key. This form of key, Fig. 75, differs from the saddle key in that it rests on a flat surface filed upon the shaft. It makes a fairly efficient fastening, but as it drives by resisting the turning of the shaft under it, there is a tendency to burst the keyed-on piece.

Sunk Keys are so called because they are sunk into the shaft and the keyed-on piece, Fig. 76, which entirely presents slipping. For engine construction they are usually rectangular in cross-section and made to fit the key-seat on all sides. When subjected to strains suddenly applied, and in one direction, they are placed to drive as a strut, diagonally, as in Fig. 77.

Round Keys. Taper-pins (Fig. 78) are sometimes used as keys to prevent rotation where a crank or wheel is shrunk on to the end of a shaft or axle. Round keys are used in such a case because of the ease in forming the key-way, which is simply a tapered round hole drilled half into the shaft and half into the shrunk-on piece. The standard pro- portions of the pins are given on page 106. The size at the large end nearest to J of the shaft diameter may be used for this purpose.

Fixed Keys are used when it is undesirable to cut a long key-way on the shaft to allow the key to be driven into place after the keyed-on piece is in position. The fixed key is sunk into the shaft, as in Fig. 79, and the keyed-on piece is driven into position after the key is in place,

When a keyed-on piece has to be adjusted to different positions on the shaft, to avoid the trouble of drawing a tight key in and out, it is made to slide in the key-way, and the keyed-on piece is held against moving along the shaft by means of set-screws, as shown in Fig. 80.

Sliding Feather Key. This system of keying secures the piece to the shaft, to transmit motion of rotation, and at the same time allows the keyed-on piece to move along the shaft. They may be secured to the keyed piece and slide in a groove on the shaft, as in Fig. 81, or secured to the shaft and slide in the groove in the keyed piece, as in Fig. 79. The dimensions for this form of key may be taken from Table 13.

Woodruff Keys. This system of keying (Fig. 2a) is used for machine tools, or wherever accurate work is of first importance. With this form of key, as the key rights itself to the groove in the keyed-on piece, there is no danger of the work being thrown out of true by badly fitted keys, and, being deep in the shaft, it cannot turn in the key-seat.

Key-heads. When the point of a key cannot be conveniently reached for the purpose of driving it out, a head is formed on one end, as shown in Fig. 76. Which shows the proportions and method of construction given in RICHARDS'S "MACHINE CONSTRUCTION."

Strength of Keys. The driving power of saddle keys or keys on flats cannot be calculated with any degree of accuracy. They are used only where the power transmitted by the keyed on piece is small.

Sunk Keys are subjected to shearing and crushing strains, and are required (1) to transmit the whole of the power transmitted by the shaft, as in crank-shaft couplings, etc., or (2) only a part of the power transmitted by the shaft, as when fastening pulleys, eccentrics, etc. As a general rule, however, all keys are proportioned to suit the first conditions, unless where the amount of power trans- mitted by the shaft is exceedingly great in comparison with that taken off at the keyed-on piece.

Cotters are keys employed to connect pieces which are subjected to tensile and compressive forces. They are driven transversely through one or both of the connected pieces and transmit power by a resistance to shearing at two cross-sections. The cotters are usually made rectangular in cross-section, and the ends rounded, as shown in Fig. 83.

The cotter-way with the rounding ends is generally adopted, as it is easier to make, which is done by drilling two holes of a diameter equal to the thickness of the cotter and cutting out the metal between them. Again, this form of cotter-way does not weaken the cottered pieces to quite the same extent as when the corners are left sharp. The cotters, however, are not so easily fitted into cotter-ways with round ends, and for that reason some engineers make the cotters of rectangular cross-section, fitted into corresponding cotter-ways.

Taper of Cotters. When cotters are employed as a means of adjusting the length of the connected pieces, or for drawing them together, they are made tapered in width, as in Fig. 83, but when used as a holding-piece only, the sides are parallel, as in Fig. 56. When tapered cotters depend upon the friction between their bearing-surfaces for retaining them in position the taper should not be more than I in 24 (1/2" per foot), but where special means are employed for holding the cotter against slacking, the taper may be made as great as I in 6 (2" per foot).

When one of the pieces connected by the cotter is a thin strap, as in Fig. 86, a second cotter, called a gib, is used. The gib is provided with a head at the ends which project over the strap S, thus preventing it (the strap) from being forced open by the friction between it and the cotter as the latter is driven into place. Figs. 86 and 89 show the application of gib and cotter to strap-end connecting-rods, where R is the rod and 5 the strap. When two gibs are used, as in Fig. 88, the sliding surface on each side of the cotter is the same. Instead of having both gibs tapered, as shown in Fig. 88, one of them may be parallel and the taper all on one side of the cotter. The strength of the gib and cotter in combination is made the same as the single cotter and should be proportional to the strap 5.

Cotter-locking Arrangements. A simple method, and one that is used in nearly all cases, where possible, is to screw one or two set-screws through the rod until the point or points press against the cotter. To keep the burs, raised by the point of the screw, from interfering with the motion of the cotter, the set-screw bears on the bottom of a shallow groove cut on the side of the cotter, as shown in Fig. 89.


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