Patent GB-548201-A (GB)
Title: Improvements in and relating to log band-saws
IPC: B27B29/10
Filed: 1941-02-28
Abstract: 548,201. Sawing. ROBINSON & SON, Ltd., T., and DEX, J. H. Feb. 28, 1941, No. 2699. [Class 145 (ii)] In a log band saw in which the timber is held on head blocks on a movable carriage and in which the head blocks are moved transversely to the carriage for a new cut when the carriage has returned to its initial position, the movement of the head blocks is effected by a double rack mechanism operated through a differential gear, the extent of the advance movement, whereby the thickness of the board to be cut is determined, being governed by a pre-setting mechanism which is automatically knocked off when the head blocks reach the cutting position. As shown the head blocks 5 are provided with racks 6 engaged by pinion 7 on the shaft 8 running the length of the machine and driven by bevel gearing from an inclined shaft 11 carrying a pinion 12 gearing with a rack 13 on a member 15 mounted in slides below the carriage 17 and carrying a second rack 18 gearing with a pinion 19 on a sleeve free in the central shaft 20 of a differential gear 21 and carrying a pinion geared to a sun pinion on the shaft 20 ; a second pinion 22 fixed to the casing of the gear and also free on the shaft 20 engages a rack 23 on the underside of the carriage 17 and is driven from a shaft 25 geared to a shaft 33 carrying a friction drive 32 eccentrically mounted thereon. The machine is driven from a gearbox 26 through a driving pulley 38a the shaft 38b of which is connected by bevel gears 38 to a shaft 27 and through pinions 39, 39a to a shaft 42 carrying pinion 40, 41 loose thereon and gearing with the pinions 39, 39a respectively; the shaft 42 carries a sliding clutch member 43 which is engaged with one or other of the pinions 40, 41 to drive the shaft 42 which is geared to the shaft 20 through worm gearing 42a and to a vertical shaft 46 through bevel gearing 45. The shaft 27 carries a friction drive 28 and the shaft 38b a friction wheel 31 engaging a friction wheel 31a on a shaft 29 also carrying a friction drum 30, the drums 28, 30 being mounted on either side of the drum 32 which may be moved by a lever 34 to engage the drum 28 or drum 30 to move the carriage 17 backwards or forwards ; the forward speed of the carriage is controlled by a lever 35 which moves the friction wheel 31a across the face of the wheel 31. The vertical shaft 46 is mounted on a pillar 37 carrying a calibrated disc 47, an adjustable stop 48, and an arm 49 adapted to be secured to the shaft 46 by a handwheel 52 and a vertical shaft 50 outside the pillar carries a hand lever 44 and is connected to a rod 53a carrying centring springs 53 and linked to the clutch member 43. The amount of forward movement of the head blocks 5 to obtain the desired thickness of board is determined by the position of the adjustable stop 48 which is moved in accordance with the calibrations on the disc 47, the arm 49 being moved to contact with the adjusted stop and then secured to the shaft 46. By pushing in the hand lever 44, the clutch member 43 is moved to engage the pinion 40 and drive the shaft 42 'and shaft 20 which through the differential gear, drives the racks 18, 13 and moves the blocks 5 towards the saw 36 ; the shaft 46 is also driven by the shaft 42 and moves the arm 49 until it engages a spring- loaded latch holding the lever 44, the latch swinging back to release the lever 44 and allowing the springs 53 to disengage the clutch member 43 and stop the movement of the head blocks. The head blocks are moved away from the saw by the operator disconnecting the arm 49 from the shaft 46 and pulling the lever 44 out so that the clutch member 43 is engaged with the pinion 41 to cause reverse rotation of the shaft 20 ; when the head blocks are moved the required distance away from the cam, the lever 44 is released and the springs 53 disengage the clutch member 43.