Following a request for an update, in the image below you can see the working version of my CNC keyboard I am using to control my Sherline mill and lathe using Mach 3. Unlike the original wired version (see original post below) this one has a Bluetooth interface and holds a battery within the box.
The keyboard works well in parallel to the standard PC keyboard and is very useful as I keep it near the mill and can watch the operation as I send commands. nevertheless, if I am to build a new one I would use smaller box and eliminate some of the less used buttons.
A KB emulator for CNC is a device built from and acts as standard keyboard with one major difference: it only has the keys necessary for basic operation of a mill or lathe and is packaged accordingly.
As shown in the pic below, I took the original interface electronics from a standard full size keyboard and added a larger PCB to avoid soldering all the wires in that small fragile board. Then I mapped the inputs and identified the connections I need in order to produce the characters (such as arrows, Atl, Ccontrol, letters and other keys).
The new keyboard goes in a much smaller box and what I made so far is the upper part while the lower one is pasted there (from SketchUp) just to show the layout. In the future I plan to replace the electronics with Bluetooth interface and place batteries in the package.
I assume that in due time I will change some of the keys as well and maybe add a joystick.