The link posted above is a zig zag seed cleaner. I built one last year from those free but very frustrating drawings. I did upgrade the triangles by using aluminum 90 degree angle stock. It works best when used to suck the chaff out of dusty seeds. It also does a fair job of pulling off immature white seeds that weigh less.
This year, I upgraded and bought a clipper office tester: https://atferrell.com/equipment/clipper/clipper-office-tester
With enough patience, you can mimic a gravity separator by bouncing a plastic box in your arms. I used to use a 12"x24" clear plastic bin. If you take a handful of material, and this works best if you have tossed it over a screen first to remove some dust, place in far end, and bounce the box up and down as you tilt from side to side, the seeds will roll out and collect on the downhill end. It is super easy, and also super slow. I had about 350 pounds of material to process, which is why I bought the Clipper. Using the box would have given me carpal tunnel before I finished.