You still need a computer in the system. Sherline uses a linux-based control software which is free to download from linuxcnc.org. You should be able to get the required setup files from Sherline. Here's a document that explains how the software works: MINI GUI

Of course, if you've only got one control box for both machines, you'll need to switch it over every time you want to switch from the lathe to the mill and back. Be sure to turn everything off and let the capacitors drain before disconnecting and reconnecting the motors.