Locating low-cost, low-tech shredders for small-scale seed threshing is next to impossible for small-scale seed production. You are left with no choice but to do all the labor manually. Marijuana seeds are tiny, so it is impractical to use a machine for threshing.
You can also try leaving your cannabis seeds to dry on a tarp, where it will naturally dehisce (shed) much of its seeds. The rest of your cannabis seeds can be manually released. Try gently whipping or rolling the plant and seeds between your fingers.
If you don;t care much about damaging your seeds, and your more concerned about time, I’ve heard some people get fast results using a weed wacker and trying to adjust the speed lower. This can be more difficult depending on which model you’re using and if its gas or electric powered.
Marijuana Seed Threshing is no joke for the high end strains, we recommend doing this manually by hand and sticky fingers! It’s very therapeutic for your soul anyways!