Understanding CNC Swiss Screw Machines and Their Functions

CNC Swiss type automatic lathes are now more powerful than ever.  They have fast cycle times and flexibility that have made them the standard and number one machine used in precision, high production applications.  Swiss machines were always preferred for long, slender turned parts, now they are widely used for small, complex parts – even pieces that have no turned surfaces. 

In a conventional lathe that has a fixed headstock, the workpiece is held in a collet and extends into the machine enclosure as a cantilever or can be supported on the end by the tailstock.  A distinguishing feature of the Swiss machine is that the headstock moves.  Bar stock passes through a chucking collet in the headstock, which clamps onto it.  The bar emerges into the tooling area through a guide bushing, which locates the bar radially during machining.  The headstock moves 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, usually within 1 mm to 3 mm.  The motion of the bar provides the feed for the 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 one or more turrets that carry more tools. 

The guide bushing supports the workpiece to maintain precision throughout the machining of the workpiece.  A physical object subjected to a force will deflect.  On a conventional lathe, if the cutting forces cause too great of a deflection, the accuracy of the cut will suffer.  When you turn parts on a conventional lathe with a length-to-diameter ratio of greater than 3:1 you should use a tailstock to prevent excessive deflection.  For any ratio greater than 6:1, you would use a steady rest or follow rest to support the middle of the part.  If you hold a workpiece securely at one end and push sideways on the unsupported end, the workpiece bends a little bit.  If you are pushing with the same force on a longer workpiece it will bend more.  The deflection for a given force increases as the cube of distance from the support to the force is twice as long with eight times the deflection.  In a Swiss machine, the guide bushing supports the workpiece so close to the tools that the deflection due to cutting forces are close to zero.  You are able to make heavy cuts and still maintain precise dimensions on the part.

Some 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
  • – Chip-to-chip time from one tool to the next cab be one second or less
  • – A single heavy cut often removes all the necessary material
  • – Surface finish can be excellent, often eliminates the need for grinding
  • – Machines with sub-spindles allows working on the back side of the part
  • – A Swiss machine can make complex parts using simultaneous operations, three or four tools can cut at the same time
  • – Most secondary operations are eliminated, since a Swiss machine can mill, drill, ream, saw and do other operations within the machine
  • – The Swiss machine can run for hours unattended after the machine is set up and the bar stock is placed in the bar loader

Medical devices are often manufactured on Swiss machines.  The United States is the world’s largest medical device market and these devices help improve surgical outcomes with advanced technologies to help make a difference in people’s lives.  Medical components are highly complex pieces that are critical to the safe operation of the device.  Medical devices include parts such as surgical needles, screws and lock plates.  Medical component specialist are experts in these high precision machine parts and can identify when tighter that necessary tolerances have been specified for these parts.

If you are running small, complex parts on your CNC lathes you might be better off using a Swiss Machine so that the lathe can be saved for larger parts.  Many new Swiss machines already run Muti-function fixed head lathes that mill and drill in addition to turning.  The controls on Swiss machines are familiar to most users and offline programming software helps users generate programs tailored to Swiss machines.  By using a Swiss machine in your operations, you can help reduce cycle times and eliminate secondaries for parts on the smaller end.  If you are looking into using Swiss machines to manufacture one of your products contact us today at https://sheldonprecision.com/request-a-quote/

Article adapted from: https://todaysmachiningworld.com/magazine/how-it-works-why-swiss/