Originally Posted by
Scott Winners
One other thing that Derek was getting at and hopefully someone said straight out. It doesn't matter what grit you sharpen to. What matters is the surface of the wood after you are done. I am "happy enough" with the surfaces I get sharpening to 4000 grit diamond, no stropping, and occasionally sanding with 220 grit or pulling out a card scraper. But I finish, mostly, with oil and waxes.
You certainly may sharpen to 30k grit on water stones if it is important to you, and it may be important to you. What matters is not the grit you sharpen to, but the surface your tools leave behind. If you are dead set on clear film finishes like shellac or polyurethane or varnish 4k may not be sharp enough. You may need to use isopropyl or acetone to lift dust out of wood pores before you apply finish. If you are going to paint a thing, you may very well find sharpening to 600 grit is more than adequate. Learn to adjust your chipbreakers so they are as close as possible to the edges on your plane irons.
One of the users here has a sig line "sharp solves all manner of problems" and I agree, but sharp in not enough to cover fundamentals. If your fundamentals are good, sharp does indeed solve all manner of problems.
Good luck and best wishes.