8 9 10 and 11 as shown in fig6 from the machine mounting surface 15 when the element 18 is rotated from the rest position illustrated with the solid line in fig5 to the operating position illustrated with the dash dotted line in the same the ball 19 is moved in the course of this rotation from the innermost part a on the cam groove 20c to the shallower part of the groove and the sheet disc 16 projects lower than said plain surface and contacts the machine mounting surface 15 when the operating member 17 is rotated under the condition that the machine body 1 is not rotated horizontally the ball 19 engages in the groove 20d as shown in fig1 and the machine body 1 contacts the surface 15 as shown in fig7 only via the sheet disc 16 under this condition the machine body 1 contacts the surface 15 via the balls 19 fitted in the ring groove 13a of the base disc 13 contacting the surface 15 via the sheet disc 16 and the engaging grooves 20d of the cam lift plate 20 if the machine body 1 is rotated horizontally the balls 19 may rotate within the ring groove 13a of the base disc 13 under the condition that the balls 19 fit into the engaging grooves 20d so that the machine body 1 may rotate by a slight force in relation to the surface 15 operation.