Those only who prepare books of the character of this realize the rapidity with which material for them accumulates. The author would not have believed, in advance, that, after an interval of three years, so extensive a revision as the one here presented would be necessary. Ignoring many minor items, some of the following subjects appear in this edition for the first time, others have been rewritten in the light of additional information and still others have been sufficiently expanded to justify their mention here.

Thrust Bearings; Knife-edge Bearings; Roller Bearings; The Critical Speed of Shafts; Tandem or Riding and Steel Belts; The Geometrical Progression of Speeds; The Strength of Spur and Herringbone Gears; Chordal Pitch; Gaging Gear Teeth; Cutting Bevel Gears with Rotary Cutters, including Parallel Depth Bevel Gears; Modified Addendum of Bevel Gears; Axial Thrust of Bevel Gears; Skew Bevel Gears; Practice with Friction-Gears; Worm Gears; Roller Chains; Friction Clutches; Spiral Springs of the Watch-spring Type; The Wire System of Measuring Screw Threads; Sizes, Properties and Strength of Wire; The Capacity of Horizontal Cylindrical Tanks, Full and Partly Full; Weirs, Rectangular and V-notch; Standard Pipe Tables; Pipe Flanges and Fittings; The Measurement of Tapers and Dovetails; Forming and Other Tools; Press Fits, Straight and Taper; Balancing Revolving Parts, including the Technique of Running Balance; The Floating Lever; Velocity and Force Relations in Linkwork; Permissible Cost of Special Shop Equipment; The Weight of Solids of Revolution; The Diameter of Shell Blanks; The Power Consumed by Drilling Machines; Taylor's Cutting Speeds; Hardness Tests, including the Relation of Brinell and Scleroscope Hardness Numbers to One Another and to the Strength of Steel; Heat Treatment of Steel including the Relations of the Heat Treatment, the Degree of Temper and the Physical Properties of Carbon Steels and the Heat Treatment and Properties of Alloy Steels; Temperature Equivalents of Temper Colors; Materials for Steam Boilers and the Proportions of Rivetted Joints; The Discharge Capacity of Safety Valves; The Properties of Superheated Steam; Steam-pipe Coverings; Approximate Beams of Uniform Strength; The Strength of Columns; Materials and Constructions for Resisting Shock. New tables will be found in many of these additions and also in the last section as follows: Whole and Fractional Inches Reduced to Decimals of a Foot; Lengths of Circular Arcs; Cutting Speeds and Revolutions; Decimal Equivalents of Prime Number Fractions; Square and Cube Roots of Binary Fractions, and Chords for Spacing Circles.

All of these additions fill gaps which needed filling, while many are fundamental and unique. The prominence of graphical methods has been retained, some of the added applications of graphics being not only time savers but, in themselves, elegant and new. All of the information contained herein, both old and new, is believed to be useful, definite and workable, much of it not readily accessible and a considerable portion of it not in existence elsewhere. The collection of design constants to be used with the rules and formulas is believed to be larger than any other, while special care has been taken, in all cases, to name the units to be used in connection with the formulas.

In books of this character there must, of necessity, be some overlapping of contents, but the aim has been to include subjects which others have ignored or treated in a fragmentary or otherwise unsatisfactory manner, while matters of common knowledge and constructions having an academic interest only have been omitted. As it is the intention that the volume shall not become a museum of antiquities, superseded material has been rigorously removed.

As the revision has gone on, the shop character of much of the material included, together with the impossibility of drawing any line of demarcation between shop and drawing office information has become more and more apparent, and the title of the book has, therefore, been changed to one which more clearly indicates its real scope. Except to make room for something better, nothing of interest to the designer and draftsman has been omitted, but, on the contrary, much has been added as the above list of subjects will show.

Defacement of the alignment charts may be avoided by the following excellent expedient suggested by S. C. Bliss (Amer. Mach., Apr. 22, 1915):

Obtain a sheet of thin, transparent celluloid about one inch smaller in each dimension than the book page and roughen one side with a piece of fine emery cloth. Place the sheet over the chart with the rough side up and rule the lines required with a soft lead pencil. The lines so ruled may be removed with a pencil eraser and the sheet thus be used indefinitely.


PREFACE TO THE FIRST EDITION

As an editor, the author's heart has often ached at the manner in which contributions to technical journals of permanent value and usefulness form a procession to the limbo of forgotten things and benefit none but those under whose eyes they happen to fall at the date of publication. This volume is primarily an effort to rescue from the oblivion of the out of print such contributions as are of direct use in the design of machinery. "The search for material has not, of course, been limited to periodicals but has extended to the transactions of many engineering societies, wherein information is nearly as effectively buried as in the back numbers of periodicals. In filling the gaps that remained after the search was completed, willing friends have come to the author's assistance.

Not only is this the way in which this volume has been prepared, but the author is convinced that it is the only way, and, more than this, that there should be deliberate co-operation between contributors, editors and collectors, with efforts focused on books of this character as the ultimate outcome.

To be more specific, the author is under no delusions regarding the many things that should be between these covers but that are not, nor of those others of which the data presented are inadequate but, now that a place has been provided for the preservation of information of the sort here gathered together, he hopes that increased activity in the preparation and the publication of such information will follow. He will certainly be glad to do his part toward the incorporation of such information in future editions. Assistance may be rendered in other ways than by preparing contributions. Wide as the search has been, it is not possible that all of the articles and papers that contain desirable data have been discovered. Those who know of such sources of information are invited to forward memoranda of the places where they may be found.