Automatic lathe
In metalworking and woodworking, an automatic lathe is a lathe with an automatically controlled cutting process. Automatic lathes were first developed in the 1870s and were mechanically controlled. From the advent of NC and CNC in the 1950s, the term automatic lathe has generally been used for only mechanically controlled lathes, although some manufacturers market Swiss-type CNC lathes as 'automatic'.
CNC has not yet entirely displaced mechanically automated lathes, as although no longer in production, many mechanically automated lathes remain in service.
General nomenclature
The term "automatic lathe" is still often used in manufacturing in its earlier sense, referring to automated lathes of non-CNC types. The first automatic lathes were mechanically automated and controlled by cams or tracers and pantographs. Thus, before electronic automation via numerical control, the "automatic" in the term "automatic machine tool" always referred implicitly to mechanical automation.The earliest mechanically automated lathes were geometric lathes, including rose engine lathes. In industrial contexts during the Machine Age, the term "automatic lathe" referred to mechanical screw machines and chuckers.
Since the maturation of CNC, the implicit dichotomy of "manual versus automatic" still exists, but because CNC is so ubiquitous, the term "automatic" has lost some of its distinguishing power. All CNC machine tools are automatic, but the usage in the machining industries does not routinely call them by that term. The term "automatic", when it is used at all, still often refers implicitly to cam-operated machines. Thus a 2-axis CNC lathe is not referred to as an "automatic lathe" even if fully automated.
Small- to medium-sized cam-operated automatic lathes are usually called screw machines or automatic screw machines. These machines work on parts that are up to in diameter and in length. Screw machines almost invariably do bar work, meaning a length of bar stock passes through the spindle and is gripped by the chuck. As the part is being machined, the entire length of bar stock is rotated with the spindle. When the part is done, it is 'parted' from the bar, the chuck in released, the bar fed forward, and the chuck closed again, ready for the next cycle. The bar-feeding can happen by various means, including pulling-finger tools that grab the bar and pull or roller bar feed that pushes the bar from behind.
Larger cam-operated automatic lathes are usually called automatic chucking lathes, automatic lathes, automatic chuckers, automatics, or chuckers. The 'chucker' part of the name comes from the workpieces being discrete blanks, held in a bin called a "magazine", and each one takes a turn at being chucked and machined. The blanks are either individual forgings or castings, or they are pre-sawn pieces of billet. However, some members of this family of machine tools turn bar work or work on centers. Regarding bar work of large diameter, it is merely an academic point whether it is called "screw machine work" or just "automatic work".
Screw machine
Screw machines, being the class of automatic lathes for small- to medium-sized parts, are used in the high-volume manufacture of a vast variety of turned components. During the Swiss screw machining process, the workpiece is supported with a guide bushing, near the cutting tool.Speaking with reference to the normal definition of the term screw machine, all screw machines are fully automated, whether mechanically or by CNC, which means that once they are set up and started, they continue running and producing parts with little human intervention. Mechanical automation came first, beginning in the 1870s; computerized control came later, beginning in the 1950s.
The name screw machine is somewhat of a metonym, as screw machines can make parts other than screws or that are not threaded. However, the archetypal use for which screw machines were named was screw-making.
The term screw machine has been redefined as the technology changes. Any use of the term prior to the 1840s, if it occurred, would have referred ad hoc to any machine tool used to produce screws. That is, there would have been no established differentiation from the term screw-cutting lathe. When turret lathes were developed in the 1840s, the term screw machine was applied to them in overlapping usage with the term turret lathe. In 1860, when some of the movements, such as turret indexing, were mechanically automated, the term automatic screw machine was applied, and the term hand screw machine or manual screw machine was retronymously applied to the earlier machines. Within 15 years, the entire part-cutting cycle had been mechanically automated, and machines of the 1860 type were retronymously called semi-automatic. From that time on, machines with fully automated cycles were usually called automatic screw machines, and eventually, in the usage of most people in the machining industries, the term screw machine no longer was used to refer to manual or semi-automatic turret lathes, having become reserved for one class of machine, the fully mechanically automated type. This narrow meaning of screw machine remained stable from about the 1890s until the 1950s. Within this class called screw machines there were variations, such as single-spindle versus multispindle, horizontal-turret versus vertical-turret, etc.
With the advent of NC, screw machines diverged into two classes, mechanical and NC. This distinction continues today with mechanical screw machines and CNC screw machines. However, in shop-floor jargon, the term screw machine by itself is still often understood in context to imply a mechanical screw machine, so the retronym mechanical screw machine is not consistently used.
Automatic chucker
An automatic chucking machine is similar to an automatic screw machine; both use spindles in production. The use of spindles, which are able to drill, bore and cut the workpiece, allows several functions simultaneously on both machines. A key difference between the machines is that the automatic chucker handles larger work, which due to its size is more often chucking work and less often bar work. The Fay automatic lathe was a variant that specialized in turning work on centers. While a screw machine is limited to around practice, automatic chuckers are available that can handle up to chucks. The chucks are air-operated. Many of these machines are multispindle.Well-known brands of such machines have included National-Acme, Hardinge, New Britain, New Britain-Gridley, Acme-Gridley, Davenport, Bullard Mult-Au-Matic, and Thomas Ryder and Son.
Automatic chuckers are a class of machine tool specialized to narrow industry niches, such as OEM part suppliers to the automotive industry. They are limited in their economic niches to high-volume production of large parts, which tends to occur only at relatively few companies. The market for such machine tools does not generally include local job shops or tool and die shops.
Cam-operated chuckers are fading into history faster than most other non-CNC machine tool classes. This is because the few companies that have them tend to be forced to continually adapt to the latest state of the art to compete and survive. Cam-op chuckers may be more likely to be scrapped than other types of non-CNC machine tools. Unlike with "Grandpa's South Bend lathe" or "Dad's old Bridgeport knee mill", virtually no one can afford to keep and use them for sentimental reasons alone. As with most nondigital commercial typesetting machinery.
Choice of machines and control type
Mechanical screw machines have been replaced to some extent by CNC lathes and CNC screw machines. However, they are still commonly in operation, and for high-volume production of turned components it is still often true that nothing is as cost-efficient as a mechanical screw machine.In the hierarchy of manufacturing machines, the screw machine sits at the top when large product volumes are needed. An engine lathe sits at the bottom, taking the least time to set up but the most skilled labor and time to actually produce a part. A turret lathe has traditionally been one step above an engine lathe, needing greater set-up time but being able to produce a higher volume of product and usually requiring a lower-skilled operator once the set-up process is complete. Screw machines may require an extensive set-up, but once they are running, a single operator can monitor the operation of several machines.
The advent of the CNC lathe has blurred these distinct levels of production to some extent. The CNC turning center most appropriately fits in the mid-range of production, replacing the turret lathe. However, it is often possible to produce a single component with a CNC turning center more quickly than can be done with an engine lathe. To some extent too, the CNC turning center has stepped into the region traditionally occupied by the screw machine. CNC screw machines do this to an even greater degree, but they are expensive. In some cases they are vital, yet in others a mechanical machine can match or beat overall performance and profitability. It is not unusual for cam-op automatic lathes to beat CNCs on cycle time. CNC offers many benefits, not least CAD/CAM integration, but the CNC itself usually does not give any inherent speed advantage within the context of an automatic lathe cycle in terms of speeds and feeds or tool-changing speed. There are many variables involved in answering the question of which is best for a particular part at a particular company.. Businesses relying on cam-op machines are still competing even in today's CNC-filled environment; they just need to be vigilant and smart about keeping it that way.
In the multispindle segment, some machine tool builders also build hybrid machines that are part CNC and part old-school control. This lets shops with certain mixes of work derive competitive advantage from the lower cost compared with all-CNC machines. The variety of machines that allow profitable production within certain niches reflects the variety of work that exists: some high-volume work remains the province of cam-op; full CNC with all the bells and whistles outcompetes on some flexible low-volume work; and hybrid machines may yield the lowest unit price on mixes in between.