Wood prep before finishing
The secret to perfect finish is proper sanding of your project. All surfaces should be clean and free from all dirt and oils. Prep sanding is done with progressively finer grits. On unfinished wood, prepare the surface by using medium grit paper first, and then progress to finer grades. With most raw woods, if you are hand sanding, start sanding in the direction of the grain using a #100-150 grit paper before staining and work up to #220 grit paper. You can make the sanding go faster with the use of Random Orbit Sander (ROS.
Soft woods such as pine and alder: start with #100 grit and finish with no finer than #220 grit
(for waterborne stains) and 180 grit for oil base stains.
Hardwoods such as maple and oak: start with #100 grit and finish-sand no finer than #180 grit
(for waterborne stains) and #150 grit for oil base stains. I have gone up to 220 grit on blotchier woods or those with high figure.
These are just some guidelines to start with, try various approaches on scrap samples to obtain the best possible outcome.
If you over sand you may seal the wood so much that it will not take a finish or stain well. Should you encounter end-grains (areas where the wood has been cut against the grain), such as the front and end edges of a table which tend to soak up more stain than other surfaces, sand with one or two grit steps up from the other surfaces. Make sure you address those end-grain areas with additional sanding to control this absorption of stain where if you do not they will be darker.
As mentioned above, you can use a ROS, along with and attached dust bag or vac to prep the wood surface and also between the coats of finish before putting on the top coat. The limiting factor is to use the correct grit of sandpaper when sanding between coats of finish.
I personally use the ROS between coat of finish with 320-400 grit to flatten any discrepancies in the applied finish levels followed by using a felt block wrapped with 400 grit sandpaper or 0000 steel wool depending on the shape, ie flat or complex. I always prefer to hand sand the final top coat starting with 400 grit working up as high as 600 grit. In both cases, always sand with the grain of the wood.
As a final step, I use a buffer and a buffing solution to blend the final coat just as they do in and auto body shop to increase the depth and reflection of light from the final finish. I also apply a coat of finishing wax like Staples Crystal Clear which to me adds a very nice mellow sheen.
The above process and result varies slightly depending on your choice of wood, finishing products rather they are waterborne or oil based, and application technique ie hand application or spraying.
Wood prep before finishing
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-- Respectfully, Paul