Pan Controls Case Studies

    Machining a variable pitch helix

Many bottling plants make use of spiral plastic worm drives to move bottles along a production line. The bottles are trapped in grooves cut in plastic scrolls. These scrolls are normally rotated at a constant speed. However it is possible to move bottles at variable speeds by making the groove pitch variable. It is even possible to rotate irregular shaped bottles by having grooves of variable cross section. Obviously making such spirals, which are usually one-offs (or actually mirror image pairs), is a difficult process.

Variable pitch scroll Gestec of Stirling have historically used CNC milling machines to mill these scrolls from solid plastic cylinders. However the process is slow, ties up expensive CNC machinery and requires considerable technician level input to set up. Fixed pitch spirals are obviously quite easy to make but some of the more complicated shapes are effectively beyond the capabilities of CNC machines.

Pan Controls have solved these problems by retrofitting a computer control system to a simple vertical milling machine. A custom computer program asks the operator for the key dimensions of the scroll to be cut. The computer program then works out detailed profiles for the full scroll shape. These profiles are sent to two motors which rotate and translate the plastic cylinder under the milling head. The result is an easily controlled and cheap machine which can cut full size scrolls in around thirty minutes compared with times of around four hours using CNC equipment.

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