A screw machine is a type of lathe used for the precise shaping of hard materials — usually metals — into specially designed components. Typically, this equipment works by rotating a workpiece at high speeds, allowing it to be operated on by various changeable cutting tools. Although there are several different types of screw machines available, they all work based on the same fundamental principle.
The term “screw machine,” however, can be a bit misleading, as these machines are used to produce a range of different components in addition to screws. In fact, threaded parts represent only a small portion of the items manufactured by this type of equipment.
Prior to the 1840s, “screw machining” was used to refer to any process that involved the manufacture of screws; however, when Stephen Fitch introduced the turret lathe in 1845, it was also referred to as a “screw machine.” In 1860, Joseph R. Brown improved the original turret lathe, which was manually operated; with the upgrade, the machine’s movements could be mechanically automated with the use of drum cams. It was around this time that the machines came to be known as automatic screw machines, with the earlier versions retronymously referred to as manual screw machines.
In the 1950s, further advancements were made as the machining process became automated via computerized controls. These advanced machines, known as CNC screw machines, also fell under the umbrella of automatic screw machines. Today, the term “automatic screw machine” is used to refer to any screw machine that runs with little to no human labor.
Types of Screw Machining Technology
Turret Lathes
These were the first types of tools referred to as screw machines. First used in the mid-1840s, they were used to mass-produce screws for the percussion locks of 30,000 pistols under a government contract. Turret lathes consist of horizontally or vertically rotating turrets fitted with different cutting tools that advance toward the rotating workpiece. Once one tool completes its operation, the turret slides back and indexes the turret to apply a different tool to the workpiece. When all the tools on the turret have shaped the workpiece, the final product is released, and another workpiece is added to the spindle. Earlier, manual versions of turret lathes are no longer used, replaced by more automated machining methods.
Cam-Operated Screw Machines/Lathes
Cam-operated screw machines are mechanically automated by a series of disc cams. Becoming popular in the late 1860s, rotating cams transform rotary movement into linear movement. As the cam rotates, linear motion is used to advance the cutting tools to the rotating workpiece. This type of equipment was the first type of automated screw machine. Although now largely replaced by CNC-operated machines, cam-operated screw machines continue to be widely used in many fabrication workshops.
CNC Lathes/CNC Turning Centers
In these screw machines, the cutting tools are controlled via computer programming. CNC lathes/CNC turning centers are also classified as a type of automatic screw machine; however, instead of relying on cams for controlling the approach of cutting tools, movement is controlled electronically via programmable user input. Popularized in the 1950s, CNC lathes are one of the most popular automatic machines, and have superseded cam-operated lathes. CNC lathes are known for their enhanced precision and accuracy, as well as their quick job changeover rate.
Swiss Screw Machines
Swiss screw machines are automatic screw machines consisting of a sliding headstock and a guide bushing. The workpiece is secured in the headstock with a collet, which clamps the workpiece and rotates it with the spindle. The cutting tools move in and out to trim the bar’s diameter and shape the overall cross-section, while the headstock moves forward and backward to create the desired length. In the 1960s, the first Swiss screw machines were automated by rotating cams, with CNC versions becoming widely available in the 1970s. Today, Swiss screw machines are one of the most popular types of screw machining technology.
Multi-Spindle Screw Machines/Lathes
These screw machines feature multiple spindles that hold, rotate, and form several workpieces simultaneously. The spindles are mounted on a rotating drum, which advances the parts to different cutting tools at various locations. The operations needed to complete the part are divided among the cutting tools in a way that allows one rotation of the drum to produce a finished product. Multi-spindle screw machines can be either cam- or CNC-operated, and they are commonly used in modern fabrication facilities where mass production and repeatable accuracy are essential.
Screw Machines Through the Ages
Since they were introduced more than 150 years ago, screw machines have seen several changes and advancements. Manual methods have become obsolete, replaced with cam and CNC automation. Although CNC machines are more commonly used and offer several advantages over mechanical cam automation, cam-operated machines are still employed in many types of machining applications.
The best option for your machining job will depend on the specifics of the application at hand.
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