Unless you really enjoy tinkering and fabrication or you live outside the continental United States, I recommend purchasing a Winnow Wizard. With multiple compound angles, <1/32″ tolerance on some dimensions, and many components to assemble, this is an advanced-level DIY project with high potential for frustration if things don’t line up correctly.
If you use the plans to build a Winnow Wizard, I ask that you send a photo and a check for $50 to Mark Luterra, 5175 SW Hillview Ave., Corvallis, OR 97333. If you make alterations/improvements to the design, please send them to me for inclusion in the plans.
**As of 2018 these plans are out of date and do not include the Wizard accessories (magnetic dirt separator and hopper agitator) and some refinements to the wind tunnel design and screen arrangement to maximize airflow uniformity. I intend to update them eventually, but at present I am focused on building Winnow Wizards for sale. If you are located overseas or otherwise unable to purchase and would like updated plans, please send me a note (firstname.lastname@example.org) and I will prioritize the update. **