Screw Machining: Quality, Quantity, Quick and Low Cost
Prior to 1873 machined parts were produced solely with lathes (machines on which work is rotated about a horizontal axis and shaped by a fixed tool). At that time, Christopher Spencer developed a one-operation automatic lathe to manufacture screws; it became known as the screw machine.
Mechanics Edwin Henn and Reinhold Hakewessel improved Spencer's concept to include four spindles (operations) through which bars of raw material could be fed. Cutting tools of these machines were advanced to cut and shape the material. Further improvements followed, and the machines began to be produced in 1896. Additional improvements were made, and the capability of the machines increased to six and eight spindles. Modern machines have from one to eight spindles and incorporate a turret and cross-slides.
Screw machines work when bar stock is fed through a collet arrangement into the machine (different types of machines require different types of collets). Single or multiple cutting tools, depending on the type of machine, turn or cut configurations on the stock to form parts. Then the machine cuts the part from the bar stock. Some parts are complete when they come off the screw machines, some parts require secondary operations.
Screw machines commonly form parts from aluminum, brass, alloy steel, free-machining steel and plastic. These materials can be formed into parts with diameters from 1/8" to 1-3/4" and from 1/4" to 22" long. The parts are used for business machines, lawn and garden tools, medical instruments, home appliance, locks, fitness equipment, firearms and sporting goods.
Rotary and in-line transfer machines are sophisticated screw machines. These machines are capable of working on both ends of a part at the same time, performing multiple processes in a single operation. This significantly reduces the cost of production. Twelve of these machines and 36 single-spindle screw machines make up the equipment inventory of our source.
Along with the variety of screw machines, a full-service firm applies Swiss-style and conventional CNC machining as well as secondary operations (broaching, drilling, grinding and milling). A toolroom is necessary to design and build gages and fixtures to support all production, injection molding and assembly operations.
Among the advantages of screw machining are quality products manufactured in large quantities with quick turnaround times and low cost. The limitations of screw machining are that they require detailed setup operations that can be expensive for small quantities. Although screw machines produce a wide range of parts, some parts may be too large to be formed on them; because of their machinability ratings, certain aerospace materials are not readily processed on screw machines. Also, certain part specifications are so precise that their tolerances cannot be maintained when manufactured on screw machines.
ISO Registrations and QS-9000 Registrations along with accepted quality control methods are indicative of a screw machining company's capability for quality products.
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