Screw machines are lathes that when automated are capable of turning materials and metals into highly precise components and parts. A lathe is a type of screw machine which holds the material or metal in one place and spins it, while moving the cutting tool across the metal. This cutting tool then sculpts the desired component from multiple sides. Screw machines were developed in Switzerland during the late 1800s to manufacture a large volume of small screws. At this time, Switzerland was the leader in manufacturing timepieces, measuring instruments, machines, and optics. These products all needed very precise parts including pins, screws, shafts, and bolts. Without the use of the screw machines, these parts would have been very expensive to produce and would not be able to maintain the same level of quality control and repeatability.
What Industries Need Screw Machining?
Screw machining is needed in virtually every industry. If it is not used in the product itself, it is highly likely used in the machines that make the product. Some applicable industries include:
Lawn and Garden (engines, mowers, snow blowers, tillers)
Marine
Medical (surgical equipment, hospital equipment, dental tools)
Fluid and Power Management
Defense and Military
Firearms
OEM
Transportation
Screw Machining Process Explained
Although the screw machining process varies depending on the part and production specifications needed, the operations are generally the same:
The workpiece (typically a rod or bar stock) locks into the machine and spins.
The spindles holding the tooling move across the workpiece, shaping it into the desired shape and size.
The workpiece passes through every spindle position until it achieves the specified dimensions.
The cut-off tool cuts off the formed part from the rest of the stock.
Finishing equipment then removes the excess debris and material to smooth out surfaces and sharpen edges.
Different Types of Automatic Screw Machines
Screw machining equipment consists of five key components: the base, the headstock, one to eight spindles, front and read slides, and the turret. Different variations of this machine design are available to suit different production applications. Below is a sample diagram:
CNC Lathe Machine Components. Photo credit to Engineering.com
There are two main types of automatic lathes:
Swiss Screw Machines are named after their origin in Switzerland where watch makers used them. In a Swiss machine, the workpiece is mounted on a rotary slide, which then turns to allow the Screw machine to cut to the required specification. Swiss machines are ideal for high precision parts. Swiss Screw Machines can be programmed to cut within a 0.0002 inches tolerance at a rate of 10,000 RPMs. This rate is not achievable with other CNC machines. The automotive industry highly depends on Swiss screw machines due to need for production of high volume parts at a low cost.
Turret Screw Machines consist of rotating turrets equipped with tooling. When one tool has completed its function, the turret slides until the next tool is indexed and can be applied to the rotating workpiece. The machine moves a length of steel rod into place to create screws, locks the turret, starts spinning, and uses tools to form the head of the screw, another tool from the side to cut the threads. Then a disk from the front to slice a screwdriver slot in the head of the screw, and lastly a cut-off tool to cut off the completed screw off the rod. Then the turret releases the screw, pushes the rod forward, locks the turret again, and repeats the process of making another screw. It requires about 10 seconds for each screw.
Benefits of Screw Machining Parts
Automation: Automatic screw machines can run with little operator oversight. They generally only require assistance during setup and changeover.
Precision: The use of a guide bushing and collet provides greater precision for turned parts than other types of lathes.
Efficiency: Swiss lathes can turn at rates greater than 10,000 RPM. Additionally, multiple spindles allow for increased efficiency of production.
Uniformity: Screw machining operations produce parts that are consistent from one piece to another and from batch to batch.
Size capacity: Turning is ideal for creating small parts that would otherwise be difficult to produce, as well as for larger parts that require attention to detail.
