Swiss Screw Machine for CNC Swiss Machining

When building

Jul 2, 2021

While in Switzerland during the 1800s, engineers devised a method for making extremely small and intricate watch parts that were also long and thin. Because the Swiss people have placed a high value on the watch industry for a long time, they developed the Swiss Lathe, which was capable of producing small parts that could not be produced on a conventional "fixed headstock lathe."Many watch parts have an unusually high ratio of length to diameter, and the small diameters necessitated turning finesse with small, specialized tooling in order to avoid breaking the watch.

Swiss Screw Machine for CNC Swiss Machining

Whenever the length to diameter ratio of a part exceeds 4:1, the fixed headstock principle creates the possibility of a part deflecting under application of tool pressure. On a conventional lathe, where the workpiece was fed out to length and then the bar was turned to a specific diameter, that was typically the limit. According to the size of the stock, the length and diameter to be turned, and the number of passes required to complete the finish diameter, you may be able to exceed the 4:1 ratio.

A part being shaped in a Swiss CNC Machining machine is depicted here. The use of a tailstock, as well as the use of a steady rest, can aid in the ability to turn longer lengths, but these two features are only effective on larger parts. When it comes to bar diameters where Swiss machines are used, we're generally talking about bar sizes up to 38mm—and the largest use bar diameters less than 1 inch.

The Swiss Automatic is known by a variety of names, including Swiss Type, Swiss Screw Machine, Sliding Headstock Lathe, and other variations. Medical instruments, bone screws, dental implants, electrical connector contact pins, watch parts, and a variety of other small, intricate, or complex parts made entirely of barstock are all produced using Swiss Computer Numerical Control (CNC) machines, which are used in several industries where nothing else would be as effective. Swiss Automatic Lathes are specifically designed for running barstock, and they typically use bars that are 12 feet in length. In many cases, these machines are equipped with automatic magazine bar feeders that can store a large number of magazines that are automatically reloaded once a magazine is depleted. When it comes to CNC Swiss Machines, high volume production is standard practice. It is an extremely rare occurrence when a Swiss is used for secondary operation work, such as re-clamping a turned part in the main spindle to perform additional work on a part.

Parts that are typical of the Swiss
The following are pieces from a Swiss turning machine. The use of a guide bushing on the Swiss turning machine, which is particularly effective for swiss machining long, slender parts from a bar, is a critical factor in its effectiveness. It is necessary to mount the guide bushing in the headstock casting so that its internal diameter (ID) is within tenths of the diameter of the bar being guided. It is clamped in a collet located in the sliding headstock, behind the guide bushing, to prevent it from moving. The bar is pushed through the guide bushing (Z Axis), and the turning tools, which are located just in front of the guide bushing, move in to a given diameter (X Axis), resulting in the turning of the workpiece occurring with almost zero deflection of the piece of work.

Early Swiss automatics used a nonrotating guide bushing, which was common in the early days of cam-driven automatics. As a result, the bar had to be centerless and ground to an extremely tight tolerance in order to maintain a consistent close fit to the guide bushing ID. The fact that the bar was rotating within a non-rotating bushing meant that there was a possibility of high friction; as a result, it was necessary for cutting oil to be directed to both the guide bushing and the cutting tools.

Modern Swiss-style turning machine builders include a driven, synchronous guide bushing that rotates 1:1 with the headstock collet, which reduces the likelihood of friction and heat buildup to a significant degree. Having said that, the majority of Swiss houses continue to use cutting oil rather than water-soluble cutting fluid. It is recommended that cutting oil be used to keep the machine lubricated and free of rust and other premature wear. Used Swiss machines lose a significant amount of their value when water-based coolant has been used, and they become extremely difficult to resell once a prospective buyer learns of the use of water-based coolant. The CNC Swiss Automatic machines of today have progressed from the original cam-driven Swiss machines, which were primarily used as turning machines. Most Swiss machines today have two spindles—the main and sub—each with an independent “C” Axis, live tooling for each spindle, and a “Y” Axis that allows the live tool to move both above and below the centerline. Several builders also include a "B" or rotational axis to accommodate a bank of tooling that is capable of performing complete features on a part.

Besides the many modern advancements in Swiss turning machines, you can also find hybrid models from several manufacturers who offer their fully-loaded machines that can be used with or without the guide bushing, depending on your preference. This is used when the number of parts to be produced in a series is relatively small, and it becomes more practical to produce the series without the use of a guide bushing. The bushing holder must be removed in order for the machine to operate without the guide bushing. This allows the headstock collet to protrude into the headstock casting, allowing the machine to operate like a fixed headstock lathe with a linear Z Axis when the bushing holder is removed. As a result, the stock can be standard mill-run material with some variation in the outside diameter.

When used Swiss machines have been subjected to high production for 8-10 years, they are typically in excellent running condition. It has been demonstrated that the use of cutting oil significantly increases the life expectancy of the mechanical portion of the machine, such as linear guide rails found on the majority of Swiss lathes. Furthermore, the small and often delicate parts do not place a significant strain on the machine, as would be the case with an 8” or 10” chuck lathe.

Most people are familiar with the brands Star, Citizen, and Tsugami—but there are several others that have a smaller share of the market (such as Tornos, Hanwha, and Nexturn) that are also worth mentioning. Normally, finding a top-of-the-line machine that is 4 or 5 years old is difficult because people tend to hold onto a well-equipped Swiss until they see significant advancements in technology before even considering selling the machine.

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When building

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