Now, it's come into its own, mainly due to the recent performance and stability improvements of Grbl v0.9. One year ago, I wouldn't have recommended using Grbl as replacement for traditional parallel port-based CNCs. I really hope that you can implement this in the future.
![grbl controller for lathe grbl controller for lathe](https://i.ytimg.com/vi/LvjxUZVf97A/maxresdefault.jpg)
It is simply because it isn't practical on the lathe with the no-threading limitation. So, it is not surprising that there isn't much use for GRBL on a lathe. On a lathe however, the lack of spindle sync means you can't thread which is a deal killer for just about every CNC lathe out there. A nuisance, but with tapping you can just pull the part off the machine and tap it using a cordless drill, or similar. On a milling machine, not having spindle sync just means that you can't do rigid tapping. Where you can have rock solid motor control from a microprocessor that is dedicated to do only that task. One year ago, I would not have considered GRBL for either of my machines and now I am convinced that something like this is the way to go. I realize that the main audience right now for GRBL is 3-axis cartesian machines, but I think you are selling yourself short. The first link has a link to a several pdf's with instructions and hookup. It is the same circuit that DAK engineering uses on turbocnc, so if you wanted to build it yourself here are some links. There are commercial boards that are available that aren't expensive at all.