Assume you are referring to separation of seed from chaff etc. I have a soil seive with interchangeable 3/5/7mm meshwhich I use. Also a tea strainer can come in handy. Always end up winnowing though, to remove chaff that’s a similar size to the seed. There’s a design for a DIY winnower on Real Seeds website – http://www.realseeds.co.uk/seedcleaner.html
Thank you Geoff, I was thinking more along your own method of a series of sieves and which size mesh for each seed as I only do a small amount such was lettuce, onion, leek, etc
I just use a bit of trial and error with various mesh sizes to take out coarser chaff first, then smaller mesh until not possible to separate seeds from chaff, then it’s on to winnowing. Just pick the mesh by eye, according to hiw big seeds and debris pieces look. Sometimes, winnowing alone will do it. Here’s a vid on leek seeds – https://www.youtube.com/watch?v=w2rHxMD8bWo