I've been obsessively browsing this forum and looking through all your incredible builds. There definitely is some great talent here, as well as sweet machines being made. This has brought up a question...
When designing a machine, specifically a vertical mill, what metric is used for rigidity? For example: if you want to design a mill capable of machining a specified material with a specified material removal rate, how do you go about this? Figuring horsepower required is much more straight forward, but there must be some metric used by commercial machine designers.