Thread: sanding level - wood and in between poly finish layers

Sand wood to 220/240 max and use 320 between finish coats. Sanding wood with very fine may be detrimental to some finishing products.

If you're using a high build finish that sits on top of the wood, like poly, then yes you are wasting your time sanding to 800 grit.

A very light rub over with 400 between coats to remove any dust nibs.

Surface finishes require a key to give good adhesion to the timber. Ultra fine sanding is detrimental and peeling or flaking will be an issue in the future.
Oils, on the other hand respond well to fine sanding as penetration is the key here. A fine sanded surface for oil will only improve the finish. 240 grit for poly and 600 for oil and you will be somewhere near it.

At my old work I think we went up to 800 between coats for oil, but anything poly we stopped at 180 or 240.

I use fine sandpapers for sharpening wood carving tools.

For finishing, I like a first coat of MinWax Tung Oil Protective Finish. Instead of sandpaper, I wait until that first coat is good and hard.
Then a gentle scrub with XXX coarse steel wool. Bulldog Brand here. The strands are thick and FLAT. The wad cuts like a thousand chisels.
Any wood fibers stuck up in the TOPF get cut off, not shredded as with sandpapers. No sanding whatsoever.
Four coats of TOPF is water wet glossy and very smooth to the touch.

For my 2C. The grit on the wood that I use depends on the openness of the wood grain and any figure in the grain. If the wood is particularly stunning then I'd maybe go to 600. Personally I don't use poly, but regardless of that and as some have said, you're really just looking to de-nib the surface between coats. One thing to be extremely careful of with poly is do not sand through a coat. If you do, you'll notice a white line around the patch where you cut through. It's at that point you sand the whole thing back to wood and start again.