The Swiss Lathe – A More Rigid Approach

What is a Swiss Lathe?

A Swiss lathe is a machine where the collet or holding mechanism is hidden beneath the guide bushing. Swiss automatic lathes, Swiss screw machines, and Swiss turning centers are all names for Swiss lathes. The holding mechanism or collet that holds a bar stock on the Swiss machine differs from ordinary lathes in that it is not exposed directly to the lathe bed and tooling. This machine design offers several advantages over conventional lathes.

In this article, we'll discuss everything you need to know about Swiss lathes: its benefits, how it works, its history, and what makes it different from conventional CNC lathes.

The Advantages of a Swiss Machine

The Swiss lathe has numerous benefits over typical lathes, one of which is the use of guide bushing. When the stock material is machined or turned, the guide bushing provides additional support. The bar-stock materials are surrounded by this guide bushing, which is snug but not too tight. Because of the support provided by the bar-stock material, the guide bushing's capabilities are comparable to those of the steady-rest on carriages on classic lathes.

A Swiss Lathe Guide Bushing - KSI Swiss
A Swiss Lathe Guide Bushing - KSI Swiss

Since turning operations are conducted close to the guide bushing, Swiss-style lathes often maintain a tight tolerance on the components. Turned parts benefit from the strength provided by the guide bushing since only a tiny portion of the stock will be exposed after they have exited the bushing and before the turning tools are engaged. The guide bushing gives the stock additional sturdiness.

Another advantage of the Swiss-style lathe is its ability to turn small-diameter components. They can also turn pieces with a greater length-to-diameter ratio. Because of the guide or tool bushing arrangement, tool chatter is reduced as well.

How A Swiss Lathe Works

In traditional lathes with fixed headstocks, a work component will be secured in a collet or chuck that will extend into the machine's enclosure as a cantilever. The other option is to use a tailstock to anchor it on one end. The Swiss lathes are distinguished from other models by their moveable headstock.

This indicates that the bar-stock will be secured onto the headstock after passing through the chucking collet. This bar then enters the tooling area via the guide bushing, which locates it radially during machining. After that, the headstock moves in a steady back-and-forth manner in a z-direction, dragging the bar behind it.

Turning tools placed on the gang slides will come into contact with this bar, which is located near the guide bushing. The feed needed for cutting action is provided by the bar's motion. The gang slides will contain the holders for fixed single-point tools and any other tools. They can even handle live tooling. Several of these machines have back-working tool stations and supplementary spindles, as well as a turret or more that can hold extra tools.

The History Of The Swiss-Type Lathe

The Swiss CNC automatics are considered the most modern and up-to-date, yet mechanical machinery has been around for more than a century. In the 1800s, as industrialization grew, there was a greater demand for interchangeable components that were produced with precision. The inventors of the era created the technology needed to help meet these needs.

The collet-chuck, which enabled the use of bar stock, was patented in 1870. The first "movable" headstock machinery was produced in Switzerland not long after. The machines were known as Swiss-type screw machines and were primarily utilized in the Swiss watchmaking industry.

These Swiss machines began to be adopted in a wide range of industries around the 1960s, and by the 1970s, the first CNC counterparts were developed. Over time, turrets and gang slides, secondary spindles, and live tooling were added to the tooling-area options. Swiss machining was popular in the electrical and semiconductor sectors throughout the 1980s.

Controls and servo motor design were improved in the 1990s. As a result, machines became more sophisticated, quicker, and stronger than ordinary machining tasks to make parts for aviation and medical applications.

Thinking Differently in CNC Lathes

When comparing CNC Swiss-type machining to traditional CNC turning, Swiss-type machining provides an entirely distinct experience. Machinists and programmers who switch from one kind to the other must change their thinking about machining cycles in several ways. Here are some factors that make them different:

The Negative Turns Into A Positive

Z-axis motions on a CNC Swiss-type lathe come from the stock moving in the opposite direction as the tool. This modification has an impact on the programming offset. Stock on conventional lathes goes out from the chuck area by preset lengths. These parts have a Z zero face, so everything you put into them will be Z negative.

Swiss Lathe Tooling Configuration for a KSI Swiss Lathe
Swiss Lathe Tooling Configuration for a KSI Swiss Lathe

Unlike Swiss machining, the turning tools will remain motionless while the stock advances. Like a conventional lathe, the faces of these pieces are Z zero, but everything beyond these faces is Z positive. This distinction is critical to remember when dealing with Z-axis offsets. This means that turning the length longer or performing a deeper drilling pass on conventional lathes requires a "minus" offset, but it requires a "plus" offset on Swiss-type machines.

The Swiss Style Lathe In Segments

With the Swiss-type, the order of the cuts that happen in a cycle would also shift. When using a conventional lathe, rough turn and finish turn jobs are usual when the machine has threads or OD grooves to produce a component. For the CNC Swiss-type lathe, this is not the case.

This is because the length of the guide bushing demands the segmentation of a part into pieces. Otherwise, when retracting the stock, the bar-stock may fall out of the guide-bushing. Segmenting typically entails cutting a part into 0.750-inch pieces, which serves as a standardized reference for the bushing-land area.

Sliding Headstock Sync with a Belt-Driven Jack Shaft - KSI Swiss
Sliding Headstock Sync with a Belt-Driven Jack Shaft - KSI Swiss

The Guide Bushing Is Crucial

The guide bushing is the most integral component in Swiss-type machines, and proper sizing is essential. This means that utilizing an improperly sized guide bushing for the task can cause concentricity issues. The guide bushing is also available in various materials, including steel, Meehanite, and carbide sleeved. As a result, possible reactions with the materials used in the workpiece must also be taken into account.

Oil Instead of Water on Swiss Machines

Most Swiss-style machines utilize oil instead of water as their cutting fluid. This suggests there will be more lubricity. Other advantages of oil are the mitigation of odor-causing bacteria growth and preventing prune-like hands caused by constant exposure to water-based coolants.

Removing heat, and chips with high pressure coolant - KSI Swiss
Removing heat, and chips with high pressure coolant - KSI Swiss

On the other hand, oil is less effective at heat dissipation when compared to water. This means that the work area of a Swiss machine can get quite heated very rapidly. As a result, if you want to do lights-out manufacturing, you'll need to outfit this equipment with fire suppression devices.

Outstanding Machine Cycles

Several new Swiss-type machinery users are quickly persuaded of their advantages when they complete a single part in one cycle that previously needed numerous machines or procedures. The Swiss CNC lathes feature seven or more axes, whereas the standard CNC lathes have 3 or 4 axes. Many shop workers utilizing these types of machinery for the first time have been astounded by the volume of work that can be done much quicker.

Deflection Correction

The goal of using a guide bushing to hold a workpiece is to keep it precise during the machining process.

Any force acting on a physical object causes it to deflect. When cutting pressures generate an excessive deflection on traditional lathes, the accuracy of the cut suffers in many cases. When turning parts with length-to-diameter ratios larger than 3:1 on a typical lathe, a tailstock is needed to avoid excessive deflection. A steady or follow rest is necessary to hold the center of a part when the ratio is larger than 6:1.

When a workpiece is securely held on one end and then pressed sideways on the unsupported end, the workpiece bends slightly. On longer workpieces, pushing with this same force causes the workpiece to twist even further.

The guide bushing for Swiss machining will hold a workpiece so tightly to the appropriate tools that cutting-force deflection will be zero. This allows the user to make larger cuts while still keeping the exact dimensions of the pieces.

High precision production - Lights Out Manufacturing - KSI Swiss
High precision production - Lights out manufacturing - KSI Swiss

Add Swiss Style Lathes Into Your Shop Today

At KSI Swiss, our Swiss lathes have a reputation for offering you more for less. We recognize the value of these types of machinery and want to ensure that our customers have the tools they require to make their components or products.

The KSI Swiss CNC machine is engineered to do the heavy lifting for you, so you no longer need to. You can produce more products and components faster than with other machines of the same type. This is why KSI Swiss only sells Swiss machines.

Sources:

  1. https://www.infobloom.com/what-is-a-swiss-lathe.htm
  2. https://www.sme.org/technologies/articles/2013/may/to-swiss-or-not-to-swiss/
  3. https://todaysmachiningworld.com/magazine/how-it-works-why-swiss/
  4. https://www.mmsonline.com/articles/understanding-swiss-type-machining