Maximum speed of gears under favorable conditions for safety is comparatively—
| Ordinary cast-iron wheels, | 1,800 | feet per minute. |
| Helical cast-iron wheels, | 2,400 | feet per minute. |
| Mortise wood cog wheels, | 2,400 | feet per minute. |
| Ordinary cast-steel wheels, | 2,600 | feet per minute. |
| Helical cast-steel wheels, | 3,000 | feet per minute. |
| Cast-iron machine cut wheels, | 3,000 | feet per minute. |
It is not, however, advisable to run gears at their maximum speeds, as great noise and vibration are caused.
Designing Gears.
This section is introduced into the work for a double purpose; 1, as an exercise in drawing; 2, as a study in accurate measurements. It is a sample of the work that the advanced student in mechanical drawing will be confronted with as he puts in practice the theory of the art of drawing.
Some sample rules are given in the following pages to aid in calculations relating to gears, and still others are given under the [section] “Useful Rules and Tables” at the end of the volume; these are to be carefully studied.
To accurately divide the pitch circle of a gear wheel by hand requires both patience and skill. On the accuracy of spacing lies the essential requisite of a good gear wheel.
The drawing in plate, [fig. 274], illustrates a pair of spur wheels, shown in gear, the office instructions for which being:
“Required, a detail plan of a pair of spur wheels; dimensions: wheel, 76 teeth, 31⁄2 inches pitch, 7-inch eye, 6 arms; pinion, 19 teeth; scale, 11⁄2 inches = 1 foot.”
The drawing, as illustrated, is the result of the above instructions, all pencil lines being removed, and this result is worked out as follows: