USING ROTARY TABLES
Direct Indexing: When performing direct indexing, the number of divisions should be divisible into the 24 fixed indexing points. Typically 2, 3, 4, 6, 8, and 12 divisions are the most common that used this style of device. If the indexing plate has 36 holes, the number of possible divisions are 2, 3, 4, 6, 9, 12, and 18.
To divide the rotation into a set number of spaces, first make sure the number of divisions will divide the total number of index points equally. Then determine the movement required for the spacing needed. For example, to space 8 points using a direct indexing device with 24 fixed indexing points, divide the indexing points by the number of divisions, (24/8 = 3). To divide the rotation into 8 equal segments requires locating in every third hole of the 24-hole plate.
Indirect Indexing: When performing indirect indexing, a much larger number of divisions may be established than possible with direct indexing. Here, the drive shaft rotation can be further divided by the indexing plates. The 40: 1 ratio of the drive shaft to the main table rotation alone permits 2, 4, 5, 8, 10 or 20 divisions. Other numbers of divisions are achieved using the indexing plates.
To divide the rotation into a set number of spaces, first determine if the number of points needed will divide the 40 : 1 ratio equally. For example, if 10 equally spaced holes are needed, the drive shaft alone can divide the circle. These 10 equally spaced holes are divided into the 40 : 1 ratio (40/10 = 4). So, to divide the rotation into 10 equal segments requires 4 complete revolutions of the drive shaft to space each division.
Other numbers of divisions require the indexing plates in addition to the drive shaft rotation. For example, if 6 equally spaced holes are required, both the drive shaft rotation and an index plate are needed. These 6 equally spaced holes are divided into the 40 : 1 ratio(40/6 = 6 2/3). So dividing the rotation into 6 segments requires 6-2/3 revolutions of the drive shaft. The 6 revolutions are accomplished with the drive shaft and the indexing plate is used to divide the drive shaft rotation into 2/3 turn for each hole. Here a plate having a hole pattern divisible by 3, such as a 18 hole circle, would work. To complete this spacing, each workpiece hole would be positioned by moving the drive shaft 6 revolutions and 12 holes in a 18 hole plate. This hole spacing can be set on the indexing plate with a movable sector arms.
Angular Indexing: some indirect indexing tasks require the rotational movement to be made in degree increments, rather that equal numbers of divisions. Here the process is basically the same, but the movement is specified in degrees. The 40 : 1 ratio of the drive shaft to the main table rotation permits 9o of table rotation for each revolution of the drive shaft (360o/40o – 9o). To further divide the drive shaft rotation, an indexing plate that has a multiple of 9 is generally used. An 18 hole circle will allow the drive shaft to be precisely moved in 1/2o or 30’ (minute) increments 9o/18 – 0.5o). Indexing plates with a greater numbers of holes will permit even finer discrimination. A 54 hole plate, for example, will allow the drive shaft to be precisely moved in0.166o or 10’ (minute) increments (9o/54 – 0.166o).
To move the rotary table a distance of 67.5o, for example, will require 67.5o/9o = 7/1/2 revolutions of the drive shaft. The 7 revolutions are accomplished with the drive shaft and the indexing plate is used to divide the drive shaft rotation. Here, 9 holes in an 18 hole plate will provide the 1/3 turn for each 67.5o segment required.
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