People often ask me which index gears they should get with their new machine – or which ones to add to their kit. I answer this question the same way I do most – by returning to first principles, and applying some analysis and math.
The 96 gear allows 11 symmetries, and is the most common, which makes more designs are available for this gear than any other. I definitely recommend this in everyone’s tool kit.
After the 96, the 120 gear allows the most possible symmetries – 14 of them. And, two others offer as many different symmetries as the 96 – the 84 and the 72.
The choices of index gears has much to do with the kind of cutting you intend to do, such as larger-number gears for repair work and very large stones, or smaller-number gears for production work in higher volumes of lower symmetries.
My recommendation is to begin with the 96 and the 120, because that offers the greatest variety, including 5 and 10 fold symmetries. To that I would add according to any specific gears necessary for cutting specific symmetries.
For instance, only the 84 will let you do 7-fold or 14-fold symmetry, and only the 72 will let you do 9-fold. So, if you’ve got a fixation with these numbers you may select one of these gears.
My personal kit includes 96, 120, 72, and 84. I know that’s four gears, but if you study the table and do some thinking you’ll make a good choice. And, you can always purchase the fourth later.
