962,164. Sanding. R. F. PENDERGAST. Sept. 9, 1960 [Sept. 10, 1959; Nov. 24, 1959], No. 31137/60. Heading B3D. [Also in Division B8] A belt tracking mechanism comprises a work roll, an idler roll mounted with its axis normally lying in a common plane with the axis of the work roll and parallel thereto, said rolls being adapted to have a belt entrained over them, control means responsive to lateral movement of a belt so entrained, and tilting means responsive to said control means for tilting the axis of the idler roll out of said common plane. The work roll is power driven and in a sanding machine it functions in association with a feed roll between the two of which work is passed for sanding. Alternatively, the driven roll may function merely as a suppport for a belt which conveys the work. In a sanding machine a workpiece 80, e.g. of wood, is inserted between a feed roll 15, which may be driven, and an abrasive belt 35, e.g. of sand-paper, trained round a contact roll 16 and an idler roll 25. The contact roll 16 has a grooved rubber sleeve 20; its shaft is journalled in side frame members 11, 12 and is driven, e.g. through a coupling. The shaft of the idler roll 25 is journalled in a yoke 31 from the centre of which projects a shaft 32 with a reduced portion 32a rotatable in a sleeve 33 slidable in a housing 34 mounted on an end frame member 13. The axis of the shaft 32 extended passes through the axis of the shaft of the contact roll 16. An extension 36 of the sleeve 33 has a pin-and-slot connection with a pivoted lever 40 extending through a slot in the side frame member 12, the lever having a handle 42 and serving to move the idler roll 25 towards the contact roll 16, for replacement of the belt 35, or away from the contact roll 16, for tensioning the belt 35, the tension being maintained by engagement of a pawl 47, pivotally carried by the lever 40, with a sloping rack 45 carried by the side frame member 12. Contact members 55, 56, which may be convex-faced skid members or rollers, are positioned below the approach flight of the belt 35 towards the contact roll 16 for engagement by the edges of the belt. The members 55, 56 are carried by levers 57, 70 pivoted on the end frame member 14, the other ends of the levers being engaged by screws 59, 72 adjustable in the ends of levers 61, 74. The latter are pivoted on the end frame member 13 and their other ends carry adjustable screws 65, 78 engaging shoulders 66, 79 on the yoke 31. If the belt 35 begins to creep to the right, Fig. 1, the member 55 is depressed by the belt 35 and through the levers 57, 61 depresses the left-hand end of the idler roll 25 to cause the belt to return to correct tracking; if the belt begins to creep to the left the right-hand end of the idler roll 25 is depressed. Instead of the mechanical linkage between the members 55, 56 and the yoke 31 the latter could be tilted by pneumatic or hydraulic cylinders located at the opposite sides thereof and controlled by valves operated by the members 55, 56. Alternatively the yoke may be tilted electrically. For adjusting the balance of the idler roll 25 about the axis of the shaft 32, a weight 90 is fixed on a rod 91 slidable in the yoke 31, the rod 91 being moved by a handle 92 and locked in adjusted position by a lock collar 93. In a modification, Fig. 6, the contact roll 16 rotates in direction of arrow 107. The contact members 108, 108a co-operate with the edges of the approach flight of the belt towards the contact roll. The members 108, 108a are carried by levers 113, 113a pivoted at 114, 114a to the frame 112 and contacting the yoke 31 through adjustment pins 65, 65a. If the belt travels to the right, the right-hand end of the yoke is depressed. In another modification, Figs. 7 and 8, the idler roll 234 is mounted in a yoke 226 secured on a shaft 220 mounted in a ball-bearing 218 carried by a frame member 216. Downwardly facing contact members 264, 266 are carried by levers 252, 254 pivoted on the frame member 216. The lever 252 carries a screw 256 and a contact pin 280 actuating a pivoted lever 276 carrying a screw 278. A similar arrangement is provided on the lever 254. The feed roll 282 rotates in the direction of arrow 286. With the contact roll 214 rotating in the direction of arrow 288, the contact members 264, 266 engage the departure flight of the belt from the contact roll. Screw 278 is advanced into contact with a lug 236 on the yoke 226 and screw 256 is retracted therefrom; the screws on lever 254 are similarly adjusted. If the belt 235 moves to the left, it raises contact member 264 and screw 278 raises the lug 236 of the yoke. If the contact roll 214 is reversed to rotate in the direction of arrow 294, the contact members 264, 266 engage the approach flight to the contact roll. Screw 278 is retracted from, and screw 256 advanced to, the lug 236 so that if the belt 235 moves to the left, raising contact member 264, the lug 236 of the yoke is depressed.