crowding. The number of sheets used must never be more than is absolutely necessary. 6. The different views should be consecutively numbered. Letters and figures of reference must be carefully formed. They should, if possible, measure at least one-eighth of an inch in height. If the same part of an invention appears in more than one view of the drawing it must always be represented by the same character. 7. The signature of the inventor is to be placed in the lower right-hand corner of each sheet, and those of the witnesses at the lower left-hand corner. The title should be written with pencil on the back of the sheet. Drawings should be rolled for transmission, never folded. On page 235, fig. 292 exhibits a reproduction of a patent office drawing, used in connection with specifi cation papers in an application for a United States patent. ENGLISH PRACTICE. The rules for patent drawings in England are practically the same as in the United States; the paper sizes are, however, different. They must be on sheets of one of the two following sizes (the smaller being preferable), 13 inches at the sides by 8 inches at the top and bottom, or 13 inches at the sides by 16 inches at the top and bottom, including margin, which must be one-half an inch wide. If there are more figures than can be shown on one of the smaller-sized sheets, two or more of these sheets should be used in preference to employing the large size. When an exceptionally large drawing is required, it should be "continued" on subsequent sheets. There is no limit to the number of sheets that may be sent in. Many of these "points" are repetitions, with but little variation from the way they have been previously stated; they are thus repeated to emphasize their practical worth. A good draughtsman leaves his work in such a state that any competent person can without difficulty ink in what he has drawn. The criterion of a good set of drawings is that with a properly prepared specification they are complete in themselves and require no explanation. A "break" in a figure or object in a drawing is shown in rough irregular lines, as in fig. 134, on page 131; this is useful when the paper is not large enough to show the whole. Having filled the pen, nearly close the nibs and try the width of the line on a piece of paper or the margin of the drawing. Never refill or lay the pen aside without first cleaning it. The application of the science of geometry to the drawing-board is absolutely necessary to success, for the reason that the whole fabric of mechanical drawing rests on the principles of geometry, which is well termed the science of measurements. Section lines should be the last inked and always without previous penciling. Center lines are necessary in working drawings. In choosing T-squares, care should be exercised to see that the head slides up and down the left-hand side of the board easily, and that when pressed against the board with the left hand there is no "slogging" of the blade up or down, or in other words, that the head is bearing firmly for its whole length against the board. The best place for the title of a drawing is said to be the upper left-hand corner; this facilitates the filing of the sheet. Never use a soft pencil except for finishing in shadow lines. The rubber should always be kept clean. Great care should be taken to keep drawing boards out of the way of heat or damp, as these cause the wood to warp. Circles and curves are to be "inked in" before straight lines. First ink the smallest and afterwards the larger curves. Do not press heavily on the pencil so as to cut the paper, but draw lightly, so that the mark can be erased and leave no trace, especially if the drawing is to be inked. The draughtsman should commence his work at the top of the paper, keeping the lower part covered over until he needs to use it. |
