Screw machines are specialized automated metalworking lathes that were first developed in Switzerland during the late 1800s to produce large numbers of identical parts such as screws. At that time, the Swiss were leading makers of measuring instruments, including timepieces and weigh scales as well as tools, machines and optics, such as microscopes and telescopes. All of these required precision-made parts including shafts, bolts, screws and pins. Without a reliable machine to mass-produce these critical parts, many products would have been far too expensive to manufacture.
The turret on a lathe is a rotatable round vise that clamps around a round part such as a shaft, spins it on its own axis, or holds it motionless and allows a tool to come in from any angle around it to perform a machining operation on the held part. The turret holds it until the entire sequence of operations is performed, at which point the turret releases the part and it drops into the bottom of the machine.
To make screws, the machine advances a length of steel rod into position, locks the turret, starts spinning, and introduces tooling to shape the head of the screw, another tool from the side to cut the threads, then from the front a disc to slice a screwdriver slot in the screw head, and finally a cut-off tool to cut the finished screw off the rod. The turret then releases the screw, advances the rod, locks the turret again and repeats the process to make another screw. Each screw takes about 10 seconds.
Once set up for a specific part, the screw machine can repeat the process quickly and precisely with little human intervention except to feed in lengths of stock. Originally the user programmed the operations mechanically with a series of cams, levers, indexing adjustments, fixturing and clamps. Each movement was precisely timed and the entire sequence set up on a master cam.
As electric motors, gearboxes and linear actuators became available, automation programs were set up electrically in much the same way a domestic clothes washer knob controls wash, rinse and spin cycles.
Most modern-day screw machines can be programmed from a personal computer and the program for a specific part downloaded to the screw machine’s own control computer over a network or phone line in seconds. Quality control measurements can be monitored automatically as the screw machine makes parts.
Source: Gill. (n.d.). Methods of Manufacturing Plastic. Small Business - Chron.com.