663,908. Grinding. SJOSTRAND, H. E. May 23, 1946, No. 2390/50. Divided 663,815. Class 60 [Also in Groups XXIV and XXXIV] In a machine for grinding plane surfaces including a'grinding wheel mounted on the spindle of an electric motor carried by an arm projecting horizontally from a vertical column on which the arm is slidable, the arm is non-rotatable on the vertical column and the latter is rotatably mounted in 'lower and upper bearings to permit arcuate swinging motion of the grinding wheel in a horizontal plane. A column 2 secured to base plate 1 has projecting arms 4, 5 with bearing holes for pivots on a swing- able column 6 of substantially triangular crosssection, slidably secured to which is a substantially cylindrical hollow arm 7 having a rectangular foot 8; bars 9, 10 secured to the foot 8 by screws 11 grip the corners of the column 6 when the screws 11 are tightened. Projections on the screws 11 are coupled by a link 14 so that both are simultaneously tightened by a single handle 15. A pivot on a head 17 fits in a cylindrical bore 16 in the arm 7, the head being looked in desired angular position by a screw 18. An electric motor 20 is secured to a plate 19 on the outer end of the head, the motor shaft carrying a grinding wheel 21. To effect vertical adjustment of the arm 7, the column 6 carries a non-rotatable screw 24 engaged by a nut journalled in the arm 7 and rotatable by a hand crank 29 through bevel gearing. The front portion of the base plate 1 has a hole 35 receiving a bearing housing 36, a flange 37 on the housing being secured to the underside of the plate 1; a sleeve 39 journalled in the housing 36 by ball bearings 41, 42, has a conical bore to receive a conical member 44 of a rotary work table 45. The sleeve 39 is driven from the grinding motor 20 through sprocket wheel 46, chain 47, chain wheel 48, intermediate shaft 49, flexible shaft 50, sprocket wheel 52, chain 53 and chain wheel 54. The sleeve 39 has a cam 40 co-operating with a sliding pin 57 carrying a head 58 on which are pivoted two pawls 62, 63 selectively engageable, by a member 64, with a ratchet wheel 65 which is connected, by sprocket wheel 68, roller chain 69 and chain wheel 70, to vertical shaft 71 to the upper end of which a slotted arm 75 is secured by a nut 74. The arm 75 is connected by link 76 with a projection 23 on the swingable column 6, so that the grinding wheel 21 swings towards the centre of the table 45 as the table rotates. By selecting a suitable length for the link 76 the speed of swing may be caused to increase towards the centre. The cam-actuated pin 57 also actuates a diaphragm pump 77 which supplies soapy water or other cooling liquid to the grinding wheel; the coolant drains into a channel 78 around the edge of the base plate, and thence by holes 79 to a container. When grinding a single large workpiece, it is secured centrally on the table 45; when grinding small workpieces, these are arranged about the table 45. In a modification, Fig. 5, the grinding wheel is swung at a constant speed, and the speed of the workholder is increased as the grinding wheel approaches the centre. The workholder is driven through gears 103, 104 by a friction disc 105 driven by a friction wheel 106 on the flexible shaft 50. The friction wheel 106 is carried by an arm 107 pivotally connected to a hub 109 swingably mounted on a pin 108. The arm 107 is lifted, to press the friction wheel 106 into engagement with the underside of the friction disc 105, by a cam 111 operated by handle 110. Automatic variation of the speed is effected by movement of the arm 107 by a cam 112 mounted on an extension of the lower bearing pin of the swingable column 6, the arm 107 being held against the cam 112 by a spring 113. Reversal of the drive is effected by a cam 115, operated by handle 116, co-operating with a finger 114 on the hub 109 of the arm 107. When a cup-wheel is used, the rear end of the motor shaft is journalled, as shown in Fig. 6, in a double axial bearing the intermediate race 140 of which is secured to the shaft by a screw 141; a spring 144 between the outer race 142 and the end of the housing 143 presses the inner race 145 against a washer 147 supported on the bearing shield 146; the radial bearing 148 permits axial movement of the shaft. The hub 150, Fig. 7, of the grinding wheel mounting has an annular channel 153 which, by centrifugal action, pumps coolant through one or more bores 154 to the interior of the cup-wheel 152.