Making or buying a cutter for internally-toothed involute ring gear cutting on the shaper?

[Xyphota]

This project is still probably 6 months away from starting but I am doing a bit of preliminary research. I would eventually like to attempt to cut internally toothed ring gears on my shaper. The only thing I'm not clear on at the moment is how the cutters for internal teeth differ from external teeth?

There are plenty of resources on making cutters for externally toothed spur gears, and even just an hour ago Clickspring released a part 1 video about how to make cutters for cutting spur gears in the home shop, but I'm unclear if these methods are applicable for internal teeth cutters?

If anyone has some resources they could point me to, it would be greatly appreciated!

 

[Susquatch]

Give the American Gear Manufacturers Association a ring.

American Gear Manufacturers Association

It strikes me that it's basically an extension of the idea of a bent rack. One or two sizes beyond flat. Your idea to use a shaper to cut the teeth might be a very practical approach.

You could also try to model involute curves to see what you can come up with.

 

[PeterT]

I went down this path evaluating options for the ring gear of my radial. They are not as straight forward as external/spur. Additional factors come into play affecting tooth shape, clearances & other dimensions, some of which also vary as a function of tooth count & pitch. Smaller PD & lower tooth counts are tweaked more if I recall & tolerances become tighter. In the end I decided to buy my way out of the problem, there was more than enough work modifying the blank never mind second guessing the tooth engagement. Not to dissuade you from pursuing. I've seen home shop broaches made and the gears apparently 'work' but the devil is in the details. How well, under what loads, their physical size etc. The formulas are generally available but the trick is translating that special shape into a tool.

Calculation of Gear Dimensions | KHK Gears

The Calculation of Gear Dimensions page covers the procedure for determining the sizes of gears. The size of a gear is defined by the module etc.

khkgears.net