If you can't see the free preview, try these things:
1. You must login with the email and password you signed up with.
2. Try a link below based on the course you're trying to preview:
- Learn the Basics CNC & CAM – https://learn.portlandcnc.com/courses/take/intro-cnc-cam/
Keep in mind, only certain lessons are available in the free preview.
There's between none and two in each chapter as shown below.