So it's ok if the dogs are simply reduced in size while squaring them up?
That's really helpful - thanks. I think we'd be silly to cut our first gear with a cutter I've made in the hope of it working with an existing set of gears, so we'll try something more simple first, but the flycutter type cutter looks like it'd be good to try in future. Links bookmarkedThree things: for most applications that are within the ability of an average home shop, an approximate involute is good enough. This is especially so if you make it specifically for the tooth count you are cutting.
This paper is interesting:
If you have any CAD ability, you can plot the correct involute, the arc approximation by the Law method and the Billhardt approximation and decide which you like best. The one Law describes is very good. We should note that he did not invent this method; it is described in the relevant old US textbooks from 1900-onwards, most of which now can be found as scans on the Internet Archive.
Second, Ivan Law's book either contains errors or is misleading (i.e. very easy to misinterpretation). These errors have been discussed to death on the Model Engineer forum, as well as on other independent websites, so you would do well to establish the facts rather than just relying on the single source Law book.
This is a good example of the derivative and correctional work:
Making gear cutters
Ivan Law in his book "Gears and Gear Cutting" describes a method for making gear cutters using two hardened steel "buttons" as a form tool. He provide tables that give the button diameter, button...mikesworkshop.weebly.com
Note the John Stevenson modification to the original method of making a single point tool (flycutter): use a cone drill from the back with good depth control and then the relief is automatically provided.
A third option for making your own cutters is to CNC mill the correct profile onto a piece of HSS with a carbide endmill. No need for any heat treatment.
