This section is from the "Modern Machine Shop Construction, Equipment, And Management" book, by Oscar E. Perrigo. Also see Amazon: Modern Machine Shop Construction, Equipment, And Management.
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 × 24 inches; quarter sheet, 12 × 18 inches; and sketching sheet, 9 × 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 × 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, 9×12 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 ¾ in. = 1 ft. or 1 in. = 1 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.
Dotted lines should have the dots and spaces of equal length and ordinarily not less than ten dots to the inch. Center lines should consist of a succession of dashes separated by two dots, the groups of two dots and one dash occupying about ⅝ 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.