Patent GB-1023455-A (GB)
Title: Improvements in or relating to tension indicators for endless bands
IPC: B23D55/10
Filed: 1961-11-21
Abstract: 1,023,455. Grinding. WADKIN Ltd., and F. W. BURROWS. Feb. 21, 1963 [Nov. 21, 1961], No. 41610/61. Heading B3D. [Also in Divisions B5 and F2] In a tensioning means for an endless belt, rope or band, particularly in a machine tool such as a belt sander or, as shown, bandsaw, wherein a tensioning wheel such as 17 is displaceable to vary the band tension, a device indicating departure from correct band tension comprises a lever 32 responsive to the tension applied through the wheel 17, a micro-switch 44 actuated by the lever, and an audible or visible warning device, such as a light 53, operated by the switch. The bandsaw comprises a saw band 18 passing round a driving wheel 16 and the tensioning wheel 17. The driving wheel is powered by an electric motor and is housed in a base frame 10 supporting a table 11. A tensioning wheel housing 13 is supported by a pillar 12 and comprises a downwardly extending saw guard 21 mounted for height adjustment on a rod 22 depending from the housing. A compression spring 29 bears at its lower end on a horizontal ledge 26 of the housing 13 and at its upper end on a collar 30 adjustably secured on an adjusting spindle 27. The lower end of the spindle 27 passes freely through the ledge 26 and is provided with a manipulating knob 28 and the upper end screws into a vertically slidable bearing block for the tensioning wheel. Thus, by turning the knob 28 the tensioning wheel is raised or lowered on the spindle 27 and by reaction through the collar 30 the compression of the spring is varied to adjust the bandsaw tension. The lever 32 pivoted at 33 on the housing 13 has, for movement magnification, short and long arms 34, 35 respectively forkconnected to the collar 30 and pivoted to a slide bar 40 carrying a cam member 41. The slide bar 40 is guided between rollers on screw posts 42 fixed to a vertically adjustable switch carrier plate 43 supporting the micro-switch 44 the operating plunger 45 of which co-operates with the cam member 41. The plate 43 is adjusted to correspond to the required band tension and is clamped in its adjusted position on the housing 13 by a wing nut engaging a stud which projects from the plate and carries a cursor co-operating with a scale bolted to the back of the housing. The switch may be arranged to signal either a condition of correct tension or of departure therefrom and to distinguish between correct tension and departure therefrom in one or both directions. The light 53 is preferably lit in the condition of incorrect tension. In operation, the switch is set to the appropriate tension by adjustment of the plate 43 and the knob 28 is adjusted until the cam member fully depresses the switch plunger for the warning circuit to signal this condition. On departure from correct tension, e.g. in the event of band stretching due to heating, the spindle 27 and the collar 30 are displaced to rock the lever 32 to actuate the switch. Correction is then effected by manipulation of the knob during use of the machine. In a safety arrangement operable in the event of sawband breakage, the switch 44 may be provided with contacts controlling two circuits, one giving the warning signal described and the other for energizing a relay for stopping the driving motor, or disengaging a clutch between the motor and the wheel 16 and applying a brake to arrest the moving parts. The switch is so constructed that with small and gradual tension changes the warning circuit contacts are actuated whereas on sawband breakage the arm 32 moves rapidly through a greater than normal amount and actuates the relay circuit contacts.