No, not really. The rotary table by itself has a vernier scale built into the handwheel, so that you can get down to degrees, minutes and seconds at any increment if desired.
Dividing plates are typically used when you want to divide a circle into a certain number of equal spaces around a part, such as when cutting shaft splines or gears. For example, if you wanted to cut a gear with 36 teeth, you would use the formula below to determine which plate to use. The plates that came with my Shars rotary table have holes as follows:
Plate A: 15,16,17,18,19,20 holes
Plate B: 21,23,27,29,31,33 holes
Plate C: 37,39,41,43,47,49 holes
N = Number of teeth on worm wheel of rotary table (usually 90 for rotary tables, 40 for indexing heads)
R = Required number of divisions (36 in this case)
T = Number of turns/holes
Formula: N/R = T
So, the numbers would be: 90/36 = T
90/36=2 and 18/36 (2 1/2)
So, we would need to turn the crank 2 and one half turns for each tooth. In this case we can use any plate with an even number of holes in it, but for consistency, let's see if we have a 36 hole plate. No. But the fraction can reduce down to 9/18 and we do have an 18 hole plate. So, I mount the 18 hole plate to the rotary table and set the pin on the crank to line up with the 18 hole circle. I would then cut the first gear tooth, then turn the crank two turns plus 9 holes and repeat the process until the gear is complete.
Let's try another set of numbers. Cutting a gear with 40 teeth. 90/40=2 and 10/40 (2.25 turns). Do we have a 40 hole plate? Nope. We can reduce the fraction down to 5/20. Do we have a 20 hole plate? Yes! So, in this case, we would cut the first gear tooth, then advance the table 2 turns and 5 holes of the 20 hole plate. Repeat until the gear is finished.
Once more, cutting 50 teeth: 90/50= 1 8/50 (1.8 turns) Don't have a 50 hole plate, but we do have a 25 hole plate, and 8/50 will reduce down to 4/25. So, we cut the first tooth, then advance 1 turn of the crank and 4 holes on the 25 hole plate, then repeat.
Clear as mud, right??
Now let's try one that's really odd: 84 teeth. 90/84 = 1 and 6/84. This will reduce down to 1 3/42 but we don't have either a 42 hole plate or an 84 hole plate. What do we do?? Simple: Make a 42 hole plate! 90/42=2 6/42 = 2 3/21 and we do have a 21 hole plate. So, we make our custom plate with a row of 42 holes, then cut our gear with 84 teeth, then save the custom plate to add other custom rows of holes as needed in the future.
For anyone that might need it, I have included a chart for 2 to 600 divisions using the plates shown above, and with custom plates identified as well. This chart is only for a 90:1 ratio as used with most rotary tables. Sorry, I did not go through the work to create one for 40:1 as I do not have a dividing head.
You will notice that there are numbers omitted from the chart because there is no possible solution with the standard or custom plates for the rotary table. So how would a person ever create such dividing plates? Some might be able to be created using an indexing head with a 40:1 ratio, while others would require the ability to do differential indexing to be able to create them. Such is the case for a 127 tooth metric transposing gear for a lathe.
View attachment Dividing Head Chart.pdf
