It sounds like you used the “Default” export scheme when exporting to DXF.
The Plasma cutter follows G-code commands. G-code supports three movements:
1 - Straight lines
2 - Clockwise arcs
3 - Anticlockwise arc
It’s your job to make sure you’re only sending supported curves to the cutter.
Lines, arcs and circles in Rhino are good to go.
Twisty Rhino NURBS curves need to be converted to arc chains. If you don’t convert them, they will be approximated by hundreds of short straight lines.
Since you need more efficient Arc objects in your DXF/DWG file, you’ll need to convert your wiggly Rhino curves to arc segments before exporting.
Use the Rhino Convert command.
Use these command option settings:
Tolerance=0.01mm or 0.002"
The tolerance controls how far the arcs will pull away from your NURBS curves. Your machining process and project will determine how much is OK. The distance is in current model units.
Then when you Export to DXF, use the “CAM Imperial” export scheme for inches and “CAM Metric” for millimeters.
Always check your DXF file by opening it in Rhino before you send it for cutting to make sure it looks good.
Another option is to export using the IGES file format. Nearly all CAM applications support curves through IGES. Choose an appropriate IGES export option configuration for your CAM application.