I became fascinated with wood lathes when I was in Junior High. I saved my money until I could buy my own lathe. Soon I wanted a bench or table saw, too. I decided to fit a saw blade to my lathe and make a table for it. The unit in the photo is not my first effort, but is an improved version.
Step 1: Blade Mount
My lathe uses a smooth shaft 5/8 inch in diameter. There is a flat spot ground into the shaft for attaching fixtures with a setscrew. Blade mandrels are available from various hardware concerns. This one slides onto my shaft and is secured with a setscrew. It has a 5/8 inch diameter threaded end with spacers, a washer, and a nut. Check your lathe. Some lathes use a hollow shaft with a Morse taper. You may need to get a special mandrel direct from the maker of your lathe.