Tool (1) for planing an optical surface (2) has a rigid support (4) with an end transverse surface (13), an elastically compressible interface (5) that is applied against and covers the end surface and a flexible tampon (6) able to be applied against the optical surface and that is applied against and covers at least partially the interface that it opposes and to the right of the end surface. The tampon includes a central part (6a) found to the right of the end surface and a peripheral part (14) found transversely on the other side of the end surface where are provided an elastic spring (15) comprising, in order to link this peripheral part to the support, a flange (18) presenting a peripheral part (22) continuously co-operating in thrust with the peripheral part of the tampon.