Tooling & Production July 2003

"Shop Talk with Steve Rose"



What is Swiss-type turning?

     How would you like the job of turning a 4” long part with a diameter of 0.059”? Did I mention you must hold a roundness of 0.0002”?
     On a Swiss-type turning machine, these dimensions and tolerances are achievable.
     Parts like this one, illustrated below, which might require numerous secondary operations can be turned complete with a Swiss-type machine.
 
     A Swiss-type lathe is not necessarily made in Switzerland. It is a type of turning center that was developed for the Swiss watch industry. These machines are designed to turn small, complex, precision parts.
     Unlike conventional lathes where the part is stationary and the tool moves, a Swiss-type turning center allows the part to move in the Z axis and the tool is stationary.
     As shown in this illustration, the bar stock is held in the machine and advanced through a guide bushing. Only the portion being machined is exposed from the guide bushing, allowing the material to be held tightly, virtually eliminating deflection -- and increasing accuracy.

     The guide bushing is the “heart” of Swiss machining, reducing chatter almost completely. Bar stock is held in the machine and fed in the Z axis to the machining position. The material is machined by the stationary tools as it moves out of the bushing. If additional support is needed, a sub spindle can move into position and grip the front end of the part.
     The type of guide bushing and condition of the material determine the quality of the fit. Close tolerance bar stock must be used and often, ground bar stock is required. Tighter fits and closer tolerances mean greater accuracy in machining.
     The availability of live tools gives a Swiss-type machine the ability to mill and drill as the material advances from the guide bushing. The machine’s Y axis provides full milling capabilities, a time saving feature that most conventional CNC lathes do not possess.
     In addition to the live tools, many Swiss-type lathes have drills and boring tools on backworking tool stations. When the part is held in the sub spindle (also called the pick off spindle), machining of the part can be finished by these tools.
     These features allow complete machining in a single operation. Although conventional CNC lathes can perform C axis live tool work, the unique design of Swiss-type machines gives the user more capabilities with greater accuracy.
     Originally designed for very small watch parts, today’s Swiss-type lathes can accommodate up to 1.25” diameter stock in machines that can run at RPM’s up to 12,000. These machines are very versatile and used in a wide range of manufacturing industries.
     These precision machines are used to make parts for the automotive, medical and electronics industry -- anyplace where small, precise parts are required. There is a large growth in the requirement for small, complex parts resulting in the swiss-type machines gaining broad acceptance in industry.
     Visit our web site for more information on swiss turning and training for this type of machining (www.cnc-training.com).
     (Our series on threading programming methods will continue next month.)