If you’re using machine shop magnetic bases on your holography table you’ve no doubt discovered that they wobble a bit.
This is a definite no-no when it comes to holography as that creates a weak point where vibration can continue to exist in your table.
The best way I’ve found to level the bases isn’t to sand them level but rather to use epoxy to let gravity quickly level them for you.
When I first found that I needed to level my bases I initially started leveling them with a method used for sharpening chisels. Get a piece of float glass or marble, attach a piece of sandpaper to it and sand the bottom of the base until it’s flat. That worked well enough but took too long.
Instead of that method use epoxy. Any quality brand will do, I use JB-Weld (which I have a few boxes of after building my new table) as my filler.
Take a piece of marble and spread a sheet of wax paper over the top. After mixing the epoxy spread a thin bead along the "skids" of the base and then lightly spread it so that it covers the skid completely.
Now put the base on the wax paper and gently press down to both even out and thin out the layer of epoxy. Let it cure overnight and it’s a snap to remove the mount from the wax paper.
You end up with a nice smooth and slightly waxy bottom that once in-place on the table, doesn’t want to move and won’t wobble as long as your table is reasonably flat.