the THCAD is a voltage to frequency converter. This resulting frequency read by an encoder input is scaled in linuxcnc to represent a voltage
Sheetcam has a materials library for plasma that lets you define the cut charts for the mateials you cut. this library included all of the setting parameters required.
QTplasmac also has a materials library. You can save your .tools in sheetcam and import them into QTplasmac. Entering data is probably easier in Sheetcam.
At the top of the sheetcam provided post processor, there are some variables that can be chnaged to deterimine where the cut parameters are taken from (from Sheetcam or QTplasmac) If QTplasmac is chosen as the master, all Sheetcam sends is the tool number and the rest of the data is retrived from the QTplasmac for that tool.
If Sheetcam is chosen as the master, all the cut parameters are passed to QTplasmac in a "magic comment" and saved to a temporary material.
Regardless of the method sheetcam uses, QTplasmac should have a copy of the tools so you canuse the conversational settings.