CNC Operator Programming a Swiss Lathe

What is a Swiss Style Lathe?

A Swiss Lathe is a type of lathe whereby the holding mechanism or collet is recessed behind the guide bushing. The Swiss lathes are also commonly known as Swiss screw machines, Swiss automatic lathes or Swiss turning centers. The Swiss lathe differ from the traditional lathes in the way that the holding mechanism or collet that holds a bar stock will not be exposed directly to the lathe bed and the tooling. This particular configuration provides this specific machine tool a number of benefits over the traditional type lathes.

The advantages of the Swiss lathe over traditional lathes are largely due to the fact that it utilizes guide bushing. The guide bushing purpose is to offer an additional support to stock material when the part is machined or turned. This guide bushing is fitted closely yet not tightly to surround the bar-stock materials. The support of this bar-stock material means that the functions of the guide bushing act in a similar fashion as steady-rest does on carriages of traditional lathes.

The Swiss-style lathes typically hold a better tolerance on the parts as turning operations will be conducted closely to the guide bushing. The guide bushing offers rigidity to turned parts due to the fact that a very small amount of the stock will be exposed once they have left the bushing and until such stage that the turning tools have been engaged. The guide bushing offers significant rigidity to the stock and these machine types are significantly well-adapted to holding a tight tolerance.

Another benefit of the abilities of the Swiss-style lathe is that they have the abilities to turn the small-diameter parts. Alternatively they can turn parts that have a larger length-to-diameter ratio. Chatter of tools is also minimized due to the guide or tool bushing juxtaposition.

How A Swiss Lathe Operates

In conventional lathes which feature fixed headstocks, a work piece will be held in the collet or chuck which will either extend into the enclosure of the machine in the form of a cantilever. The other way is that it will be supported on the one end with a tailstock. The distinguishing factors of the Swiss machines to other types are the fact that the headstock moves.

This means that the bar-stock will pass through the chucking collet positioned in the area of the headstock that it will be clamped onto. This bar then emerges in the tooling-area through the guide bushing that locates this bar radially while machining. This headstock then moves in a precise back-and-forth motion in a z-direction while taking the bar along with it.

Turning tools that are carried on the gang slides will make contact with this bar in close proximity to the guide bushing. The bar’s motion offers the feed required for the cutting action. The gang slides will carry the holders for the fixed single-point tools or any of the other tools and can even support the live tooling. Many of these machines use back-working tool stations and secondary spindles and in some cases a turret or more that is able to carry additional tools.

The History Of The Swiss Style Lathe

The Swiss CNC automatics are recognized as the modern and latest thing, however, the former mechanical machines have been used for over a century. In the era of the 1800’s industrialization increased which resulted in the need for parts that were interchangeable that were manufactured with precision. The inventors of this time developed the necessary technologies to assist in meeting up with these demands.

In 1870 the collet-chuck was patented which allowed for the use of the bar stock. Shortly after this, the very first of the “moving” headstock machines were created in Switzerland. The machines were named Swiss-type screw machines that were used mainly in watch-making industries.

Around the 1960s these Swiss machines started to be used in many other industries and by the 1970’s the first CNC versions were released. As time went by the tooling-area choices started to include the gang slides and turrets, secondary spindles and live tooling. In the 1980’s Swiss machines began to be used extensively for the production of parts for the electronic and semiconductor industries.

In the 1990s improvements were made on the design of the controls and servomotors that resulted in more advanced, faster and stronger machines in order to produce parts for aerospace and medical applications over and above the typical machining work.

Thinking Differently in CNC Lathes

When comparing the conventional CNC turning to the CNC Swiss-type machining, the Swiss-type machining offers a very different experience. The programmers and machinists that shift from the one type to the other need to alter the way they think about the machining cycles in numerous ways. Here are a few of these differences:

1. The Negative Becomes A Positive

On the CNC Swiss types Z-axis motions are derived from stock moving opposed to the tool. This particular change has an effect of the programming offset nature. On the conventional lathes stock extends out from the area of a chuck by specified lengths. The face of these parts is Z zero and anything into this part will be Z negative.

In contrast with the Swiss machines the turning tools will be stationary as the stock will advance. The face of these parts is Z zero like conventional lathes but anything beyond these faces will be Z positive. This difference is very important to keep in mind in association to the Z-axis offsets. This means making drilling pass any deeper or turning the length longer involves a “minus” offset on conventional lathes but will necessitate a “plus” offset on Swiss-types.

2. The Machine In Segments

The order relating to the cuts that occur in a cycle will also change with the Swiss-type. With the conventional lathes it is standard to finish turn and rough turn work when the machines features threads or OD grooves in order to complete a part. This is not the same when it comes to the Swiss types.

This is because the guide bushing length requires that a part will need to be segmented into sections, otherwise the bar-stock could fall-out from the guide-bushing when retracting the stock. The segmenting usually will mean machining a part into sections of around 0.750 inch which is standardized guide for the bushing-land area.

3. The Guide bushing Is Very Important

Guide bushing is known as the central part of Swiss type machines and sizing is vital. This means that using guide bushing which is incorrectly sized for the job can result in various concentricity errors. The guide bushing also comes in different types of materials that include Meehanite, steel and carbide sleeved. This means the potential interactions with work piece materials are another very important factor that needs to be considered.

4. Oil Opposed To Water

The majority of the Swiss type machines will use oil for their cutting fluids opposed to water. This means that the lubricity will be greater. The benefits of oil include the freedom from the odor-causing type bacteria growth and to prevent prune-like looking hands caused from exposure to the water-based coolants on a daily basis.

However, one main downside when compared to water is that oil is not as effective in dissipating heat. This means that Swiss machine cutting can become hot quickly in the area of the work zone. This means that equipping these machines with fire-suppression systems is a necessity if you plan on lights-out manufacturing.

5. Outstanding Machine Cycles

Many new Swiss-type machine users soon change their mind on the benefits of these machines when they complete one part in a single cycle that usually required multiple machines or multiple operations. The conventional type CNC lathes typically feature 3 or 4 axes. While the Swiss types will have 7 or more axes. Viewing the amount or work that can be performed a lot faster with the machine in smaller work zones has amazed many shop personnel who start using these types of machines for the very first time.

6. Deflection Correction

The aim in supporting a work piece with a guide bushing is to do with maintaining precision throughout the process of machining on the work piece.

Physical objects that are subjected to any force will naturally deflect. When it comes to the conventional lathes, when cutting forces have caused a deflection that is too great, the accuracy associated with the cut will in most cases suffer. The accepted rule with conventional lathes is that when parts are turned that have length-to-diameter ratios which are greater than 3:1, a tailstock is required to prevent any excessive deflection. For the ratios that are greater than 6:1 a follow rest or steady rest is required in order to support the center of a part.

If a work piece is held securely on the one end and then pushed sideways on the end that is not supported, the work piece will bend slightly. When pushing with this exact force on longer work pieces the work piece will bend even more. Deflection for the given force will increase when the cube-of-distance that comes from the support onto the force will be double in length and 8 times this deflection. This means when applying a side force on the end of a 2″ part it will usually deflect 0.001″, while the very same force when applied to the end of 4″ part with the exact diameter will result in a 0.008″ deflection.

When it comes to the Swiss machines, the guide-bushing will support a work piece so closely to the necessary tools that deflection caused from cutting forces is actually zero. This means that the user can use heavier cuts while still maintaining the precise dimensions on these parts.

Adding Swiss Style Lathes Into Your Shop

For businesses that run complex and small parts on CNC lathes, these companies can experience faster machine cycles, and more profit with a Swiss machine that will free up these lathes for more appropriate and larger parts. For example, many shops may feature up to 10 conventional CNC lathes and in many cases the parts that are made could be easily be produced on the Swiss machines. In most cases the business could benefit from running just about all these parts on two Swiss machines opposed to the 10 conventional CNC lathes.

A variety of the newer Swiss users now operate fixed-head lathes that are multifunctional that drill and mill over and above turning. What is great about these Swiss machines is that they are familiar to many of the users and the offline programming-software assists the users in creating programs that are tailored and designed for Swiss operations.

In the majority of cases the new users seem to be extremely satisfied of the productivity related to Swiss machines as well consistency in the parts including the superior quality of the surface finish.

Dependent on sizes of the parts that are produced and the mix related to the type of jobs a company conducts, one or two Swiss machines can not only decrease cycle times but also eliminate the need for secondaries for the parts on smaller ends of the range. These machines also offer the advantage of freeing up other equipment in a shop in order to produce the larger parts.

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