I have noticed that the bandsaw gives nice even particles of the right size. It gives good consistency for sanding, and makes good filler,too. I have several varieties in different containers; purpleheart, maple, fir, and pine.

Joe Greenley uses a putty filler instead of wood flour. I forget exactly what kind, but it's on his website. The putty soaks up epoxy after it hardens, and matches the wood color better.