I am a luthier. Along the edge between the top and the sides of an instrument, we luthiers like to install a binding. It serves as a protective edge and adds to the value and beauty of the instrument. A groove must be cut for gluing the binding, so that it is flush with the top and sides. The width and depth of the cut must be precise.
I have a friend who has an attachment that he bought from a guitar builders supply. It has a large base that holds the Dremel square with the top. It also has an adjustable roller which controls the width of the cut, while guiding the Dremel along the curved sides of the instrument.
I think that Dremel could make a better, more affordable attachment for this job.
Let's make something.