http://www.forum.simplify3d.com/viewtop ... f=8&t=1949
Reasons why computer to USB transmission should be a secondary choice to SD card printing:
Main reason-->USB cables are prone to EM interference- If too many transmissions get dropped in the back-and-forth the firmware will go unresponsive.
Computer's sleep settings may be on
Laptop could run out of battery
Automatic system updates restarting the computer
If your processor lags (playing a video game that requires high performance)- transmission could be interrupted
Accidentally closing the software
Computer freezing due to another program
I would highly highly highly suggest you don't use four printers from the same USB port as the reasons listed in the above list. However, you can do this by opening up separate instances of Simplify3D by opening up the Terminal and typing in the following:
"open -n /Applications/Simplify3D-2.2.2/Simplify3D.app" (Without the quotes)
This will open separate instances of Simplify3D that won't interfere with one another, so you can have four different printers being controlled by one computer.