accident than a smaller one. But if the drawings are too small they must often represent the work on so small a scale that the lines and dimensions will be crowded, and necessitate small letters and figures, whereby the liability to errors by the workmen is much increased.

It is, of course, much more convenient to handle and to care for small drawings than large ones, both in the shop and in the drafting room, and the smaller sizes are not nearly so liable to injury. If we assume that the whole sheet or unit of our sizes is 24 x 36 inches, we may conveniently obtain the following sizes with no waste of drawing paper, tracing cloth, or blueprint paper, namely: double sheet, 36 x 48 inches; whole sheet, 24 x 36 inches; half sheet, 18 x 24 inches; quarter sheet, 12 x 18 inches; and sketching sheet, 9 x 12 inches. Ordinarily, construction drawings can be confined to the first two sizes, while for very large sheets a quadruple size of 48 x 72 inches may be used. These large sizes will readily fold to fit in a drawer suitable for 24 x 36 inch sheets, which will be preferable to rolling them. In folding such drawings care should be taken not to press the folds so firmly as to cause deep creasings, with the danger of the paper giving way by repeated folding. The best sizes for use in the shop as well as for handling in the drafting room will be found to be 18 x 24 inches and 24 x 36 inches, the former having the preference. It is advisable to confine the drawings for the shop to one size if it can be done without sacrificing convenience and efficiency to the demands of uniformity.

In the manufacture of small parts in large numbers it is often a matter of great convenience to use thick cards, 9 x 12 inches, with round corners, upon which a drawing of a single piece is made. The drawing is varnished on both sides with at least two coats of bleached shellac, that on the back preventing the warping of the cards due to the varnish on the face. These cards are convenient to handle and store and are economical, as no mounting is required, and they are much more durable than might be supposed.

When drawings are not made full size, the question of the most desirable scale should be carefully considered, with a view to selecting one not so large as to fill the sheet too much, or so small as to crowd the various parts shown. That scale is best with which the draftsmen may work with least liability to error. Many find that the scale of half size, or 6 in. =1 ft., is very unfortunate in this respect, and most of them will no doubt prefer the quarter scale, 3 in. 1 ft., whenever it can be used. The eighth scale, 1 in.=1 ft., is properly a favorite where a smaller scale is desired, while the general drawing of a large machine completely assembled may require a scale of 3 in.=1 ft. or I in. ft.; but this will seldom occur in the usual course of machine drawing.

The scale should always be clearly marked on every sheet. If it is drawn

full size, that should be stated. The fear that machinists will measure a drawing rather than depend on the figures and thereby make errors in the work is a needless one under nearly all circumstances, and is largely overbalanced by the convenience of having the scales plainly indicated in all instances. It is equally important that the dates be given. On a construction drawing the date when it is commenced and when it is completed should both appear. On all other drawings the date should be that of completion. This should be supplemented by the dates of alterations made on the drawing and the dates of the original tracing, and any subsequent ones made necessary by such changes.

All drawings should show when and by whom the dimensions are checked. The name of the draftsman should appear in full on all construction drawings and his initials on all other drawings or tracings. These precautions will often greatly facilitate following up a design and the subsequent changes in connection with it.

Considerable controversy has been had on the point whether shade lines are appropriate on mechanical drawings. When the arguments are all in it would seem but fair to say that there is no good reason why they should not be used and several very good reasons why they should. One reason only appears necessary for using them they make the drawing much easier to read by the machinist, hence there is less liability to error, and less time is spent by him in deciphering complicated drawings.

spaces of equal length and ordiCenter lines should consist of a

Dotted lines should have the dots and narily not less than ten dots to the inch. succession of dashes separated by two dots, the groups of two dots and one dash occupying about inch. Spaces as above. Dimension lines should be a series of dashes separated by one dot, and of lengths and spaces as above. All dimensions up to 3 feet should be given in inches and common fractions of an inch; dimensions greater than 3 feet, in feet, inches, and common fractions of an inch.

When work requiring fine measurements is to be drawn it will be found necessary to use decimal dimension figures rather than to use the smaller common fractions of an inch therefore the use of decimal fractions should be encouraged. For fine work they are practically indispensable. The numerator and denominator of a common fraction should never be separated by a diagonal line, but always with one parallel to the dimension line. Gothic figures should always be used, the lines of which should be of equal width throughout. Figures should read properly when the sheet is so held that the title reads properly. When this cannot be done they should read properly when the sheet is turned with its right-hand edge next to the reader.

Sections may be distinguished on tracings by going over the back of the

tracing with a soft lead pencil, depositing enough of the lead to show well in the blueprint. If it is desired to distinguish the material of which the part is made we must resort to section lining conventionally adapted to this purpose. The mose useful of these forms are shown in Fig. 179. It will be noticed that the method is to represent similar materials by similar forms of lining, which assists in memorizing the forms; also, that the more common materials are

the more simple and easy to represent. Some draftsmen prefer this plan and in addition using the soft pencil on the back for increasing the effect. It adds but little to the time of making the tracing.

Another much discussed question of drafting room practice is that of titles on drawings, and what may or may not be considered proper as to the matter to be included. On this subject opinions vary all the way from the use of a simple serial number to matter enough to constitute a veritable history in brief. There are several points to be considered in the matter. The title should contain enough information to be of practical use and at the same

time to tell its story briefly. It should tell us what set of drawings it belongs to, naming the machine; what part of the machine it represents; the scale to which it is drawn, and the date when it was completed.

On construction drawings the date when it was commenced should also be, given. It should show what draftsman drew it; when and by whom it was traced, checked, and altered. It should give the name of the establishment. Then we shall not have to refer to an index book, or to a card index whenever we wish to ascertain any of these facts; and as the foremen or workmen are not provided with these useful accessories they will not have to annoy others, or to go to the drafting room to ask questions about it, as would frequently be the case if blueprints contained, as titles, only such marks as "24-A-5," meaning that it belonged to machine No. 24, could be found in drawer A, and that it was sheet No. 5, all of which is of very little use to the man in the shop who uses it, however sufficient it may be in the drafting room.

Yet it is of use to have each machine distinguished by a symbol, or letter, and the particular tracing and blueprint by a number. These numbers begin with 1 for each machine, hence they do not usually run into more than two figures. They are a convenience to the draftsmen in finding them in the drawers, as well as of designating them briefly. This form of title is shown in Fig. 180. The plainest lettering should always be used, hence the gothic form for important letters and figures, and the draftsman's italic for the smaller ones, will be the most economical to make, the easiest to read, and consequently the best adapted to practical use both in the shop and in the drafting room.

12" ENGINE LATHE.

GENERAL DRAWING OF

HEADSTOCK.

Scale, 3"=1 ft.

Drawn by
L.T.F.
6-12-'04

Traced by G.T. 6-14-'04

Name of Company.

Checked

by J.K.M. A 2

6-15-'04

FIG. 180. Title on Drawings. Usual

size, 2x 3 in.

Many methods have been advocated and experimented upon to determine the best way to mount blueprints for use in the shop. One method is to have boards half an inch thick with cleats nailed to the ends, and not increasing the thickness of the boards. These boards are painted on both sides and have the blueprints laid upon them and held down by pine strips 1 x 3 inch, fastened with 8-ounce carpet tacks, for easy removal. This method renders the blueprints very convenient for the shop and preserves them well, as the strips prevent their defacement by other boards coming in contact with them. However, blueprints mounted in this manner occupy considerable space.

Another method is to mount the blueprint on heavy strawboard or binders' board. In this form an extra sheet of equally strong paper should be pasted on the back of the strawboard to prevent warping. Blueprints mounted in this manner are quite convenient to handle in issuing, returning, and storing,

and with even heavy strawboard they are light and convenient for the shop. The corners should be clipped off or rounded.

Still another method is to mount the blueprint on sheet iron. This has been tried with blueprints of moderate size, but it would seem that these can not be very convenient to handle on account of their weight, and would be liable to injure each other if piled up, by defacing the lines and figures. The edges of the sheet iron will be rather harsh to the hands. If properly performed the method of mounting blueprints upon heavy strawboard will be found as good as any for sizes of 18 x 24 inches and 24 x 36 inches, while for small work the 9 x 12 inch cards as described above will be found very useful.

Several systems are in vogue for indicating the different machines built, and these symbols are carried into the system of the drafting room for the purpose of identifying drawings. One of these methods is by distinguishing figures, another by letters, and more frequently by letters and figures combined, the one representing a class and the other indicating its place in that particular class. It will need no argument to prove that the more simple this symbol can be the easier it will be remembered, the less time it will take to represent it on drawings, and the less space and expense will be required to attach it to patterns.

When the number of different machines to be built does not exceed thirty or forty the letters of the alphabet may be very conveniently used; in the more frequent cases a single letter only being required. This will be readily scen from the scheme which follows, and is adaptable to a shop building machine tools in a moderate variety.

The letters I, O, and X are omitted for the reason that the letter I is so near in appearance to the figure 1, and the letter O to the cipher, that they are likely to cause confusion. The letter X is omitted as it is used to indicate changes in a pattern, as will be presently described. Other machines may