Keebler, I looked briefly into CAM with OnShape right when I first started looking at it last year and IIRC, it required a 3rd party add-in or application. Seems like it was a little pricey and might only work with a paid subscription to OnShape (?), which is more expensive than a F360 subscription.
For most CNC work, you really do not need 3D drawings unless you want to create contours or relief carvings. For the most part, simple 2D drawings are all you need. Let me know what want to do and I can see if I can help you get headed in the right direction. Feel free to call me if you want.
--Nathan, TX. Hire the lazy man. He may not do as much work but that's because he will find a better way.