Casting Study: Lawn Edge Trimmer

The innovative Qualcast Lawn Edge Trimmer, the design of which is patented, is entirely based on zinc castings, which are used for both drive train and housings. The trimmer is attached to the standard Concorde mower by replacing the existing belt drive cover with a strong and rigid two part assembly of zinc castings. The trimmer mechanism is housed within a zinc body which clips onto the cover castings when required. The existing tooth belt pulley is replaced by an ingenious mechanism which relies on zinc castings for its operation. The motor drive is transmitted from the shaft mounted central drive dog casting to the body of the main casting by a spring loaded ring. This mechanism provides automatic disconnection of the cylinder mower drive with trimmer fitted. The outer teeth of the main gear casting engage the drive belt driving the cutting cylinder. The inner interrupted teeth transmit power to the trimmer attachment. This pair of castings also accurately locates a central roller bearing. On attaching the trimmer to the housing a cast gear compresses the spring loaded ring and engages the inner teeth of the driven gear. A train of zinc cast gears then transmits the drive to the cam which operates the cutter blades. The Edge Trimmer design relies on the precision with which zinc can be cast to provide the accuracy of profile and the meshing of the zinc gearing plus the location of the bearing. It also relies on the strength, stiffness and wear resistance of zinc alloy together with its ability to provide an attractive appearance.