Bill Tindall, E.Tn.
It is for some drug- who pays attention- and as usual as they are warning that one of the side effects is that your toes, or whatever, will fall off. The actor cured by this wonder is sanding a guitar. He is making too-short awkward passes with the grain when suddenly he quickens the pace and sands across the face to the other side.

In the next scene his is proudly presenting the instrument to a grandchild? . The surface is not revealed in the scene, just the happy faces.