OK, to sand or not to sand? Water or no water?
My simple answer to this has a complicated explanation:
- Yes, "raise the wood grain" with water (rubbing alcohol does the same because it has water in it). A small amount of water on the surface won't warp the shaft.
- Yes, once it is dry, sand with very fresh, very fine sandpaper, 800 to 1000 grit.
But why? That's the complicated part.
When your shaft was made, it was invariably sanded on a lathe or by hand in the process. This leaves microscopic tears in the wood surface. Imagine wood is made up of tiny, tiny cells that resemble straws or bamboo. These get crushed, torn and flattened by sand paper, especially old coarse sand paper. They feel smooth to the touch until water from the atmoshere and sweat absorbs into these straws cells and they balloon up, creating the bumpy surface we call "raised grain".
So if you want a smooth shaft and you sand without raising the grain, you will do so again and again and again until you don't have a shaft left. It will keep getting bumpy.
However, if you wet the wood surface, allow it to dry, then sand off this raised grain, maybe even a couple of times, now you truly have a smooth surface, even if the wood gets moist.
Don't believe me? Take a smooth shaft and wet it, let it dry for a couple of minutes and feel it. You should feel bumps from the raised grain. Lightly sand these off with fresh 800 grit. Repeat the process, after wetting and drying you will feel fewer bumps from the grain raise. Do it a 3rd time. This time you probably won't feel any bumps after wetting and drying. You've removed the torn fibers that create the rough surface and water won't affect the surface anymore.
So by raising the grain with water and lightly sanding, you will prevent the need to do so again for a long time. The friction of your bridge hand will eventually cause the need to do it at some point but it could be years if properly sealed with the methods discussed.
The pic below shows the cell structure of wood from an electron microscope. There are fibers sticking up that, if wet, will enlarge and become "raised grain". This is typical of cut and sanded wood. If wood is planed or sliced, the problem is not as great.
Here's a link to better understand the process:
https://www.woodshopnews.com/columns-blogs/grain-raising-can-be-just-a-bump-in-the-road