Indeed more surface is large more one will may find it beneficial to use the sander, but attention has never not to station at the same place.

In general, and this some is the type of grain used, the arm must always be moving, of before behind, of left on the right or in circular motion.

Well cavity one will start with a grain of 80 on a surface to scrape well to see at worst of the 60 but have the light arm.

Do not seek especially has to obtain a good result with this type of grain it is not useful which work has to trim (as for painting plusieures master keys will be necessary for a good result).

One will finish work with the orbital or vibrating grinder with a grain of 80 for small surfaces, on the other hand for great surfaces it will be preferable to make an intermediate passage has the sander with also a grain of 80.