What is a Swiss Lathe? Comprehensive Guide

What is a Swiss Lathe? Comprehensive Guide

What is a Swiss Lathe? Comprehensive Guide

Swiss lathe originated in Switzerland in the 1870s for the primary purpose of producing parts for the watch industry.

Due to their high precision and low margin of error, Swiss lathes are now popularly used all across the globe for various different applications.

But what makes these lathes special and how are they different from conventional lathes?

In this article, I have discussed Swiss lathe machines in detail such as their design, capabilities, and applications.

In the end, I've also laid out the differences between a Swiss lathe and a conventional lathe machine to help you compare them and choose the one suitable for your application.

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What is a Swiss Lathe?

Swiss lathes are high-precision lathes, ideal for machining small and intricate parts. In these lathes, a sliding headstock advances a segment of the workpiece into the tooling area through a guide bushing while the rest of the workpiece is held firmly inside the chuck.

Interior of APSX Nano CNC Swiss lathe (Source: APSX)
Interior of APSX Nano CNC Swiss lathe (Source: APSX)

In Swiss lathes, the cutting tool remains stationary while a high-speed rotating bar stock moves back and forth to execute the machining operation.

This is one key aspect where Swiss lathes differ from conventional lathes.

Swiss lathes use a segmented machining approach that provides firm clamping of long workpieces, thereby preventing them from deflecting under the application of strong cutting force.

These lathes also reduce material wastage by allowing you to use small and thin bar stocks for machining small parts, which otherwise could not be machined on traditional lathes.

Swiss lathes are generally used for machining metals and are therefore considered as a type of metal lathes.

When compared to wood lathes, metal lathes are characterized by high spindle torque and a relatively less speed (RPM).

However, wood lathes can also be used for machining metal workpieces but the availability of metal lathes in various types like center lathe, turret lathe, swiss lathe, etc., provides them an advantage even over the best wood lathes.

Despite their complex working and high precision, Swiss lathes are also available at competitive prices, comparable to conventional lathes.

APSX-NANO is one such affordable swiss lathe that can be used for machining of various materials like aluminum, stainless steel, brass, plastics, etc.

Design of Swiss Lathe

Construction of a typical Swiss Lathe
Construction of a typical Swiss Lathe

The key components of a Swiss lathe are the guide bushing and sliding headstock.

Guide bushing is fixed in the headstock cast and is manufactured in such a way that the inner surface holds the bar stock firmly.

The workpiece is clamped in a collet located behind the guide bushing in the sliding headstock.

It is forwarded into the tooling area via the guide bushing where the tool relocates to the required distance from the center of the workpiece for the turning process.

The tools work very close to the guide bushing, which prevents the deflection of the workpiece under the cutting force.

Furthermore, advanced Swiss lathe machines are equipped with two spindles—main and sub.

The main spindle is used for the primary machining on the part and then transferred to the sub-spindle in case of additional machining operations.

However, the main and sub-spindle must be perfectly aligned to prevent damage to the workpiece or machine.

Factors that Differentiate Swiss Lathes from Conventional Lathes

In the table below I have summarized the differences between a Swiss lathe and a conventional lathe.

ParameterSwiss LatheConventional Lathe
Offset in Z-axisPositiveNegative
Order of machiningSegmented approachOne operation at a time
performed on the whole workpiece
Guide bushingPresentAbsent
Cooling liquid OilWater
Cycle timeLowHigh
Post-processingLittle to noneMay be needed for complex parts

Quick summary of the differences between Swiss lathe and Conventional lathe

Offset in Z-axis

Workpiece coming out of the guide bushing
Workpiece coming out of the guide bushing

In a conventional lathe, the workpiece is extended out from the collet chuck by a certain length and the face of the workpiece is considered as a reference (0 on the Z-axis). 

The tool travels from the face of the workpiece towards the collet chuck. This is considered as a movement in the negative Z-axis.

Hence, you should use a negative ("-") sign for Z-axis offsets when programming for a conventional lathe.

In Swiss machining, the sliding headstock advances the workpiece into the tooling area through the guide bushing.

Similar to a conventional lathe, the face of the workpiece is still considered a reference (0 on the Z-axis).

However, the movement of the workpiece out of the chuck is considered a movement in the positive Z-axis, opposite to that of a conventional lathe. 

This means that you have to use a positive ("+") sign for Z-axis offsets during Swiss lathe programming.

Segmentation

Generally, in conventional lathes, the operations are performed in sequential order. The next operation is performed only after the first operation is completed.

This means the workpiece is turned, then the tool is changed to make the grooves wherever needed.

This workflow is a better option for conventional lathe as the whole workpiece is accessible to be worked on at all times. 

In Swiss machining, the sliding stock makes it impossible to follow this workflow as the whole workpiece is never accessible at once.

Because of this, a segmented approach to machining makes more sense in a Swiss lathe. The size of a segment is usually 0.75", which is the standard land area of a guide bushing.

For example, when using a swiss lathe for turning and making grooves on a workpiece.

Flow of Segmented machining on Swiss lathe
Flow of Segmented machining on Swiss lathe

Swiss lathe first performs turning on segment 1, then changes the tool and makes the required grooves in the current segment.

Then the next segment of the stock is pushed out through the guide bushing, and the tool is changed accordingly to perform the turning and grooving operations in the next segment.

Segmenting is also required to prevent the stock from falling out of the guide bushing while retracting.

Guide Bushing

Guide bushing used in Swiss lathe
Guide bushing used in Swiss lathe

Guide bushing is one of the characteristic parts that make Swiss lathes stand out from conventional lathes.

In conventional lathes, workpieces are set up in the main collet and this may cause deflection of the bar stock if the length to diameter ratio is greater than 4:1.

Swiss lathe reduces the overhang and deflection to almost zero by working on the workpiece very close to the guide bushing.

Guide bushing provides firm support to the workpiece, thereby allowing deep cuts in a single pass rather than multiple shallow passes. This increases precision and reduces tool wear.

Depending on the required level of accuracy, guide bushings are of three types: rotary, fixed, and high-precision guide bushings.

Rotary guide bushings rotate along with the workpiece and are best suited for turning wide features.

When compared to the other two, rotary guide bushings offer the least precision and are used for applications with a tolerance of around ±0.0005" or higher.

Fixed guide bushings remain stationary and the bar stock rotates inside it.

They should be adjusted such that bar stock is in full contact with the bushing and, at the same time, shouldn't be too tight to stall the spindle.

Fixed guide bushings are used when higher precision (more than 0.0005") is required.

High-precision guide bushings, as the name suggests, are used for even tighter tolerances. This is usually required for machining of parts that are to be used in medical devices.

Cooling Liquid

Unlike conventional lathe machines, Swiss lathes use oil-based coolant instead of water.

The purpose of a coolant is to transfer the heat from the cutting edges and avoid the bar stock from overheating to prevent dimensional changes.

Oil provides greater heat absorption than water, making it ideal for metalworking applications where high dimensional accuracy is required.

It also provides higher lubricity than water, which helps reduce tool wear and prevent rusting of parts. This increases the life of the tools and reduces maintenance of the machine.

Cycle Time

Different axes in a Swiss lathe machine
Different axes in a Swiss lathe machine

In the case of Swiss machining, the moving stock increases the number of axes of operation, thereby providing a higher degree of freedom.

The typical axes of operation for a Swiss lathe range from 7 to 13, compared to 2-5 axes for conventional lathes.

Swiss lathe can perform multiple operations like drilling, slotting, milling, end-face grooving, and back drilling in a single pass.

The ability to perform multiple machining operations on in a single setting reduces the cycle time and improves the productivity of Swiss lathes.

Post-Processing

When using conventional lathe machines, complex parts generally need to be processed on different machines before attaining the final product.

Swiss lathe, on the other hand, has around 30 tools that can work on the material. This eliminates the need for the part to be worked on by other machines.

Furthermore, Swiss lathes provide better surface finishes in a single pass without the need for secondary finishing processes.

As a result, the parts manufactured on Swiss lathes have a 'ready-to-ship' quality.

Material Conditioning for Swiss Lathe

Maximum allowed bow of a stock for Swiss lathe
Maximum allowed irregularity of bar stock for Swiss lathe

Swiss machines are best suited to manufacture small parts with tight tolerances. The bar capacity usually ranges between 0.08" (2mm) to 1.5" (38mm).

Swiss machines can create details as small as 0.0003" and repeatedly turn diameters up to 0.003".

An important requirement of Swiss lathe machines is that the bar stock needs to be consistent in diameter throughout its length.

Even if the bar is undersized by a few millimeters, it should be undersized along the entire length by the same amount.

The bar stock that is fed into the Swiss lathe should be as straight as possible. However, it can handle a maximum bow of 0.001" per 12" of length.

If an inconsistent bar stock is used in a Swiss lathe, the part created will also be inconsistent.

A conventional lathe machine can be fed with an inconsistent bar stock as it can be centered and turned till it becomes uniform. This operation is not possible on a Swiss lathe.

Advantages of Using a Swiss Lathe

There are several benefits of a Swiss Lathe when compared to conventional lathe machines.

Swiss lathes were initially designed to machine small and detailed parts with very tight tolerances, such as parts used in the watch industry.

The guide bushing allows you to use a bar stock that has a length-to-diameter ratio greater than 4:1 without deflecting the bar stock, which otherwise is not possible on conventional lathes.

A segmented workflow approach and high surface finish eliminate the need for secondary machining.

The ability to mount multiple cutting tools and a higher degree of freedom ensures a low cycle time, which means Swiss lathes can output a greater number of parts with better precision than conventional lathes.

final thoughts

Swiss lathe machines give some very definitive advantages over conventional lathe machines.

The segmented approach of Swiss lathes, along with the multi-axis cutting system, and the ability to hold multiple cutting tools offer various advantages over conventional lathes.

However, this increases the complexity of the process and therefore requires an experienced machinist to operate these machines.

The G-code to control Swiss machines optimally tend to be very complicated as there are many more things to keep in mind.

Furthermore, programming such complex tasks can be tedious and requires a thorough understanding of the machining operation.

One such task is transferring the part from the main spindle to the sub-spindle.

Perfect synchronization during the transfer has to be ensured to prevent damage to the machine or part.

Conventional lathe machines are ideal for manufacturing heavy-duty parts whereas Swiss machines are ideal for smaller but highly complex parts.

The stock used on a Swiss lathe should be uniform both in diameter and length, whereas conventional lathes provide some freedom when it comes to the irregularities of the bar stock.

frequently asked questions (FAQ)

How are Swiss lathes different from conventional lathes?

Swiss lathes differ from conventional lathes in the way they operate. In a Swiss lathe, the workpiece can rotate and slide along the Z-axis, whereas in a conventional lathe, the tool moves and the workpiece remains stationary.

What are the applications of a swiss lathe?

Swiss lathes are ideal for machining small workpieces with complex geometries, that are generally used in medical devices, hydraulic valve parts, medical implants, musical instruments, shafts, watches, and electronics.

Can a Swiss Lathe work without a guide bushing?

Yes, there are hybrid Swiss lathe machines that can run without a guide bushing. These Swiss lathes behave like a fixed headstock lathe as the bushing holder is taken off and the collet projects into the headstock cast. This way of operation is more practical when a series of parts are to be manufactured in a short period of time.

About John

Hey I'm John. I talk about CNCs and Power Tools at Mellowpine. I'm a CNC hobbyist who has been making CNCs and writing about CNCs for a while. I currently also work as a consultant for business owners and hobbyists setting up their own CNCs. If you have any questions related to CNC, I'd be happy to answer them. Reach me at john@mellowpine.com

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John

Hey I'm John. I talk about CNCs and Power Tools at Mellowpine. I'm a CNC hobbyist who has been making CNCs and writing about CNCs for a while. I currently also work as a consultant for business owners and hobbyists setting up their own CNCs. If you have any questions related to CNC, I'd be happy to answer them. Reach me at john@mellowpine.com

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