DISK DIAMETERS FOR ANGULAR MEASUREMENT
| Deg. | Inch | Deg. | Inch | Deg. | Inch |
|---|---|---|---|---|---|
| 5 | 1.0912 | 17 | 1.3468 | 29 | 1.6680 |
| 6 | 1.1104 | 18 | 1.3708 | 30 | 1.6983 |
| 7 | 1.1300 | 19 | 1.3953 | 31 | 1.7294 |
| 8 | 1.1499 | 20 | 1.4203 | 32 | 1.7610 |
| 9 | 1.1702 | 21 | 1.4457 | 33 | 1.7934 |
| 10 | 1.1909 | 22 | 1.4716 | 34 | 1.8262 |
| 11 | 1.2120 | 23 | 1.4980 | 35 | 1.8600 |
| 12 | 1.2334 | 24 | 1.5249 | 36 | 1.8944 |
| 13 | 1.2553 | 25 | 1.5524 | 37 | 1.9295 |
| 14 | 1.2775 | 26 | 1.5805 | 38 | 1.9654 |
| 15 | 1.3002 | 27 | 1.6090 | 39 | 2.0021 |
| 16 | 1.3234 | 28 | 1.6382 | 40 | 2.0396 |
| Machinery | |||||
Disk-and-Square Method of Determining Angles
The method shown in [Fig. 15] for determining angles for setting up work on a milling machine or planer, possesses several advantages. No expensive tools are required, the method can be applied quickly, and the results obtained are quite accurate enough for any but the most exacting requirements. As will be seen, an ordinary combination square is used in connection with a disk, the head of the square being set at different points on the blade according to the angle that is desired. Theoretically, a one-inch disk could be used for all angles from about 6 degrees up to a right angle, but in practice it is more convenient and accurate to employ larger disks for the larger angles.
The only inaccuracy resulting from this method is due to setting the square at the nearest “scale fraction” instead of at the exact point determined by calculation. This error is very small, however, and is negligible in practically all cases. The dimension x required for any desired angle a can be found by multiplying the radius of the disk, by the cotangent of one-half the desired angle, and adding to this product the radius of the disk.
Example: The square blade is to be set to an angle of 15 degrees 10 minutes, using a 2-inch disk. At what distance x ([see Fig. 15]) should the head of the square be set?
Cot 7 degrees 35 minutes = 7.5113,
and 7.5113 × 1 + 1 = 8.5113 inches.
By setting the square to 8½ inches “full,” the blade would be set very close to the required angle of 15 degrees 10 minutes.
Locating Work by means of Size Blocks
The size-block method of locating a jig-plate or other part, in different positions on a lathe faceplate, for boring holes accurately at given center-to-center distances, is illustrated in [Fig. 16]. The way the size blocks are used in this particular instance is as follows: A pair of accurate parallels are attached to a faceplate at right angles to each other and they are so located that the center of one of the holes to be bored will coincide with the lathe spindle. The hole which is aligned in this way should be that one on the work which is nearest the outer corner, so that the remaining holes can be set in a central position by adjusting the work away from the parallels. After the first hole is bored, the work is located for boring each additional hole by placing size blocks of the required width between the edges of the work and the parallels. For instance, to set the plate for boring hole D, size blocks (or a combination of blocks or gages) equal in width to dimension A₁ would be inserted at A, and other blocks equal in width to dimension B₁ beneath the work as at B. As will be seen, the dimensions of these blocks equal the horizontal and vertical distances between holes C and D. With the use of other combinations of gage blocks, any additional holes that might be required are located in the central position. While only two holes are shown in this case, it will be understood that the plate could be located accurately for boring almost any number of holes by this method.