To Find Center Distance for a Given Angle.—When straight-edges must be set to a given angle α, to determine center distance C between disks of known diameter. Rule: Find the sine of half the angle α in a table of sines; divide the difference between the disk diameters by double this sine.
Example: If an angle α of 20 degrees is required, and the disks are 1 and 3 inches in diameter, respectively, find the required center distance C.
| 20 | ||
| —— | = | 10 degrees; sin 10° = 0.17365; |
| 2 |
| 3 - 1 | ||
| ————— | = | 5.759 inches = center distance C. |
| 2 × 0.17365 |
To Find Angle for Given Taper per Foot.—When the taper in inches per foot is known, and the corresponding angle α is required. Rule: Divide the taper in inches per foot by 24; find the angle corresponding to the quotient, in a table of tangents, and double this angle.
Example: What angle α is equivalent to a taper of 11/2 inch per foot?
| 1.5 | ||
| —— | = | 0.0625. |
| 24 |
The angle whose tangent is 0.0625 equals 3 degrees 35 minutes, nearly; then, 3 deg. 35 min. × 2 = 7 deg. 10 min.