The primary goal of sanding is to produce a surface that doesn’t show machine marks or sanding scratches after you apply a stain or finish. If the scratch pattern can be made even, you may achieve satisfactory results sanding only to #150 grit. Stationary sanding machines are best for doing this, though hand sanding will also work, especially if you aren’t applying a stain.
The main reason you sand wood before applying a finish is to remove machine marks. All machine tools leave cuts or impressions in wood that are highlighted by stains and finishes, especially by stains. Before machine tools appeared in the mid-nineteenth century no sanding was needed. Indeed, there was no sandpaper. Wood was smoothed with hand planes and scrapers.
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