702,299. Internal grinding. AMMCO TOOLS, Inc. Nov. 21, 1951 [Nov. 29,.1950 ; July 31, 1951], No. 27313/51. Class 60 A rotary hone for internal grinding comprises a cylindrical body member 32, Figs. 3 and 6, longitudinal slots 40 therein, abrasive units 51 mounted for longitudinal movement in the slots, and cam elements 54 on the units for co-operating with openfaced cam surfaces 46 disposed on opposite sides of the slots so that the units move radially outward in response to longitudinal movement in one direction, such longitudinal movement of the units being effected by actuating elements 70 which are movable longitudinally in the slots and detachably engage the units. The body member 32 has a screw-threaded connection 30 with a tubular drive shaft 14 which houses a push rod 26 for operating the elements 70. Two camming surfaces 46 are provided on each side of each slot 40 and are formed by transverse notches 47 cut in the body, Each unit 51 consists of an abrasive face 50 on. a carrier 52 which on each side carries two integral lugs 54, Fig. 10, forming the cam elements for co-operation with the surfaces 46. Additionally, the units are provided centrally in their underfaces with lugs 60 which are housed in a central through-passage 44 in the body member, and, in the contracted position of the units, the inner faces of these lugs are in engagement. Each actuating element 70 is formed of a strip of spring material having a curved forked end 78 which straddles a lug 60 and engages projecting inclined faces 68 on the latter ; the opposite end of the element 70 is hooked at 74 for engagement, between the end of the push rod 26 and a cylindrical guide 80 which fits over an extension pin 82 on such rod and is urged against the rod by a spring 86. Pressure on the rod 26 acts through the elements 70 to move the abrasive units to the right in Fig. 3 and expand them. Upon release of this pressure, the spring 86 contracts the elements and so withdraws the abrasive units to inoperative position. In the modification shown in Fig. 12, the abrasive units 136, which are similarly disposed in longitudinal slots 122 in the body 113 and have camming engagement 128, 146 with the latter, are retained on the body by two rings 152 of synthetic rubber disposed in grooves 144 in the units. Fingers 154 for expanding the units are disposed in the slots 122 and provided with out-turned ends 156 engaging the ends of the units ; the opposite ends of the fingers are connected to a head 160 fitted on a stop pin 110 which has a lost-motion connection 170, 172 with a push-rod 106. A compression spring 168 is compressed in pre-loaded condition between the head 160 and push-rod 106, and a spring 166 of less strength is disposed between the body 113 and a split ring 162 on the stop pin. Normally, the spring 168 acts to position the head 160 and stop pin 110 as shown relatively to the push rod 106 and maintains this relative position when the latter advances the head 160 so as to expand the abrasive units, the spring 166 then being compressed without affecting the spring 168 until the stop pin engages the body 113. Should the abrasive units be in engagement with the cylindrical surface to be ground and a force be applied to the push-rod greater than is necessary to expand the hone, the lost-motion connection 170, 172 and spring 168 permit relative movement between the push rod and stop pin 110.