Engineers in this country state dimensions of machines in feet, inches, and fractions of an inch, the latter being the 1⁄2, 1⁄4, 1⁄8, 1⁄16, &c. In making calculations it is generally more convenient to use decimal fractions, and then substitute for the results the equivalent fractions in eighths, sixteenths, &c. The following table will be found useful for this purpose:—
Decimal Equivalents of Fractions of an Inch.
| Fraction | Decimal Equivalent | Fraction | Decimal Equivalent |
|---|---|---|---|
| 1⁄32 | ·03125 | 17⁄32 | ·53125 |
| 1⁄16 | ·0625 | 9⁄16 | ·5625 |
| 3⁄32 | ·09375 | 19⁄32 | ·59375 |
| 1⁄8 | ·125 | 5⁄8 | ·625 |
| 5⁄32 | ·15625 | 21⁄32 | ·65625 |
| 3⁄16 | ·1875 | 11⁄16 | ·6875 |
| 7⁄32 | ·21875 | 23⁄32 | ·71875 |
| 1⁄4 | ·25 | 3⁄4 | ·75 |
| 9⁄32 | ·28125 | 25⁄32 | ·78125 |
| 5⁄16 | ·3125 | 13⁄16 | ·8125 |
| 11⁄32 | ·34375 | 27⁄32 | ·84375 |
| 3⁄8 | ·375 | 7⁄8 | ·875 |
| 13⁄32 | ·40625 | 29⁄32 | ·90625 |
| 7⁄16 | ·4375 | 15⁄16 | ·9375 |
| 15⁄32 | ·46875 | 31⁄32 | ·96875 |
| 1⁄2 | ·5 | 1 | 1·0 |
Engineers use a single accent (´) to denote feet, and a double accent (´´) to denote inches. Thus 2´ 9´´ reads two feet nine inches.
II. RIVETED JOINTS.
Two plates or pieces to be riveted together have holes punched or drilled in them in such a manner that one may be made to overlap the other so that the holes in the one may be opposite the holes in the other. The rivets, which are round bars of iron, or steel, or other metal, are heated to redness and inserted in the holes; the head already formed on the rivet, and called the tail, is then held up, and the point is hammered or pressed so as to form another head. This process of forming the second head on the rivet is known as riveting, and may be done by hand-hammering or by a machine.
Forms of Rivet Heads.—In fig. 1 are shown four different forms of rivet heads: (a) is a snap head, (b) a conical head (c) a pan head, and (d) a countersunk head.
Proportions of Rivet Heads.—The diameter of the snap head is about 1·7 times the diameter of the rivet, and its height about ·6 of the diameter of the rivet. The conical head has a diameter twice and a height three quarters of the rivet diameter. The greatest diameter of the pan head is about 1·6, and its height ·7 of the rivet diameter. The greatest diameter of the countersunk head may be one and a half, and its depth a half of the diameter of the rivet.
