I do all my designing in openscad, currently for 3d printing, but now would want to use these same designs on my cheap 3018 cnc machine. What is the best and easiest method of doing this?
Something like Cura but for Subtractive Manufacturing.
You could try Fusion 360, I believe the trial software is still free up to a certain number of files. There are alot of Youtube tutorials to help you learn modeling and toolpathing. Important to be aware going in that .stl files are tough to translate into something that sort of software can use. The two things are sort of parallel in that they use G code, but are seperate disciplines due to the need to build a tool library and understand the speeds and feeds associated with different tools for machining rather than the single tool (generally speaking) you’re working with in 3D printing.
This is, of course, an over simplification of the relation between 3D printing and machining but I hope it might give some idea of what you’re diving into.