Swiss screw machiningCNC Swiss-type automatic lathes are more powerful than ever - while retaining the fast-cycle times with the same flexibility that makes them a standard for most precision, high-production applications.

Today even more tools and greater options are available. Sophisticated controls usher streamlining into the machining process. Swiss screw machining is always preferred for the longer, more slender turned parts, widely used for smaller, highly complex parts and works well for the pieces that have no turned surfaces at all.

Conventional lathes have a fixed headstock. The workpiece itself is held in a chuck or collet. It extends into the machine enclosure working as a cantilever. It can also be supported on the end - by the tail-stock.  

To distinguish a Swiss machine from others in its class - observe it's headstock move. A bar-stock passes through a chucking collet in the headstock - which clamps onto it.

Why Swiss Screw Machining So Valuable?

Swiss screw machining means that the bar emerges into the tooling area through a guide-bushing which locates the bar radially during machining. 

The headstock then moves very precisely back-and-forth in the z-direction - taking the bar with it.  The turning-tools carried on gang-slides contact the bar very close to the guide bushing.

The bar motion provides feed for this cutting action. Gang-slides carry holders for fixed single-point or other tools and may support live-tooling.  Many machines have a secondary spindle back, working tool stations and sometimes one or more turrets that carry more tools as well.

The purpose of supporting the workpiece with the guide bushing is to maintain precision throughout the machine workpiece. 

Any physical object subjected to a force - will deflect. On conventional lathes, if the cutting forces cause too great a deflection - the accuracy of the cut suffers.   If you hold a workpiece securely at one end - then push sideways on the unsupported end - the workpiece bends a certain amount.   Push with the same force on a longer workpiece - it will bend more. 

With Swiss screw machining - the guide bushing supports the workpiece so close to the tools - that the deflection due to the cutting force is essentially zero.  The result means you can take heavy cuts and still maintain precise dimensions on the part.

Swiss turning is used to make small, slender, complex and precision components.  This is possible due to unique design.  In the Swiss turning machine - the bar-stock material is gripped tightly and advanced by the sliding headstock through a guide bushing to the machining section. 

The machining section consists of stationary tools which are applied to the emerging bar stock.  Because only part of the bar to be machine is exposed from the guide bushing - there is minimum deflection. This allows the turning of small, accurate precision parts. 

If the part is longer and needs more grip support at the front end, a sub-spindle can be applied to grip it. This reduces deflection during cutting.  Accurate and close tolerance parts are possible with tight-tolerance guide bushings and finely-ground bar stocks.

The advantages of CNC Swiss machines come from both the guide bushing and the geometry and mechanics in the tool zone.

Depending on the machine there may be room for 20 tools or more in the tool zone. Higher-end machines also have tool changers available. 

Since the machines are relatively compact and the tools don't have to move very far, the chip-to-chip time from one tool to the next - can be one second - or less. 

Usually, a single heavy cut removes all the necessary material. Surface finish can be excellent. It often eliminates the need for grinding. A machine with a sub-spindle allows working on the back side of the part.

  • A Swiss machine can make complex parts using simultaneous operations.
  • It is able to have up to three or four tools cutting at the same time.
  • Swiss machines are extremely versatile.

They are used to make small precision-parts with complex part-configuration and profiles for industries like:

  • Medical
  • Dental
  • Defense
  • Electronic 

This reduces cost from extra secondary operations.

In most cases secondary operations are eliminated since Swiss screw machining can mill, drill, ream, saw and do other operations within the machine. The part comes off the machine ready to ship. 

Swiss screw machining allows complete machining to be finished in a single operation through the incorporation of milling capabilities in the Y-axis and drills and boring tools on the back tool stations.

Setup times are relatively short. Machining a family of parts could take 10 minutes to change from one to another.  Other changeovers might take an hour or two.  Since your Swiss machine may have 20 or more tools mounted,  plan your tooling so that all the tools needed for several jobs stay right in the machine.

Once the machine is set up and the bar-stock placed in the bar-loader, your Swiss machine can run for hours unattended. 

On a Swiss screw machine, you machine the part from one end to another.  Because the work is supported right next to the tool - you can safely take heavy cuts on a Swiss machine where on a lathe you’d take multiple cuts while trying to keep cutting forces low enough in a single pass without any backtracking. 

The dimensional quality of your parts will, to some extent, depend on the straightness and roundness of the bar you use.  

Crescent Industries provides precision Swiss screw machined components that have tight tolerances, high surface finishes and complex geometries.  Click here to learn more about our Swiss Screw Machining capabilities.

Topics: Swiss Screw Machining