GB779483A - Improvements relating to power hack saw machines - Google Patents

Abstract

779,483. Sawing. CASH, G. H. April 25, 1956, No. 12646/56. Class 145 A power-operated hack saw comprising a saw frame 19 reciprocable on an arm 16 pivoted at 15 is provided with a hydraulic dashpot 32 for relieving the saw blade 20 during the return stroke and with ratchet means 45, 48 which, at the end of a cutting operation, are rendered operative so that during continued reciprocation of the frame the successive relieving actions raise the arm step-by-step to an elevated position ready for a further sawing operation. The rack 45 may be mounted on the arm 16 and the pawl 48 on the machine frame 10 but preferably the rack is carried by a fixed bracket 25 having a slot 27 cooperating with a headed pin 28 to support the arm laterally. In the lowest position of the saw frame a trip 53 moves the pawl 48 to operative position, in which it is held by a spring-pressed plunger 51 snapping over a projection on the arm 16. In the raised position of the frame, the arm 16 opens a switch to stop the driving motor and the pawl 48 may be arranged to close this switch again as it is manually disengaged from the ratchet 45 to allow the saw to descend on a fresh workpiece. The saw frame 19 is reciprocated by a crank rod 24 and a crank disc 22 on a shaft 21 also carries an eccentric 29 oscillating a link 31 by which the dashpot cylinder 35 is raised during each return stroke of the frame. The dashpot piston 36 has a non- return valve 44 and a needle valve 41 adjustable by a handle 43 so that the amount of relieving action can be adjusted, the handle 43 being linked to the pawl by a rod 53 and adjustable abutments 56, 57 so that movement of the pawl to operative position closes the valve 41 and causes the relieving action to be a maximum when lifting the arm 16.