Switzerland is famous for high quality watches, and tiny, high-precision screws contribute to their success. Today, though, the machine tool technology developed to make these intricate parts is used to produce a host of other items too.

This blog explores how Swiss screw machining is a cost-effective way of producing high quality parts for industries as varied as hydraulics, manufacturing machinery, and medical devices. It should answer your questions if you’d like to know more about the best way of making intricate cylindrical parts. First though, an introduction to the special characteristics of the Swiss screw machine.

Multispindle Turning

A Swiss screw machine is a type of multispindle lathe. Like all lathes, it produces cylindrical parts by turning diameters and performing operations on the end face. Like other multispindle lathes, it’s fed with bar stock loaded into a series of tubes arranged in a circular drum. The drum indexes between positions, moving the exposed length of bar from one station to the next.

At each station, one or more cutting tools perform an operation. This could be forming grooves or chamfers, turning down a diameter, or possibly boring or drilling on-axis from the end.

This ability to machine complex shapes gives designers an opportunity to consolidate other separate parts into a single piece.

Unique Bar-Feed Mechanism

The bar feed and guide bushing mechanism make Swiss machines especially suited for producing high precision parts.

Each bar is gripped and fed by a collet. This pushes the bar through a guide bushing into the cutting zone. Unlike other turning operations, a Swiss machine can feed the bar forward as it’s being turned. It can also lock in a fixed position or rotate through a precise angle.

Control over bar rotation allows drilling perpendicular holes and milling flats. Bar feed control means the cutting tools don’t need to move axially: instead the bar provides that Z-axis motion.

Bar feed control also enables something called “segmented machining”. Rather than push the full length of workpiece out of guide bushing, only a short length protrudes. This is turned, after which another length is moved out. This minimizes deflection under cutting forces, which gives Swiss machines their high precision capabilities.

Characteristics of Swiss-Machined Parts

The bar feeding mechanism restricts the maximum workpiece diameter. For our machines, this is 1-1/4” (32mm). However, there’s room inside the cutting zone to feed out up to 12” (600mm) of the bar. These characteristics, in conjunction with the many tooling options, make these machines ideal for producing high length-to-diameter aspect ratio parts with complex features.

These parts will have excellent straightness and concentricity, thanks to the guide bushing and because there’s no need to regrip between operations. Accuracy is +/- 0.0004” (0.01mm), although tighter tolerances may be possible, depending on part design. (Contact us to discuss your needs.)

Surface finishes can be extremely good. This results from eliminating deflection and vibration, plus the use of large cutting tool nose radii to reduce cutting forces.

Most ferrous and nonferrous alloys can be Swiss-machined. This includes stainless and carbon steel, brass, aluminum, and even titanium.

Applications by Industry

Swiss machining is ideal for long, thin, primarily cylindrical, parts. (We say primarily because it’s possible to mill flats and even hexagons on a round bar.) Here’s a list of industries using Swiss machined parts and some of the applications:

• Hydraulic equipment (valves and pumps) – valve spools, pistons, sleeves, couplings
• Automotive (including large engines) – fuel injection system components, shafts, sleeves, actuator rods and linkages, valve stems
• Aerospace (airframe and engines) – connectors, shafts, screws, press nuts
• Medical equipment and devices – specialized screws for implantation, nuts, bolts, actuator rods
• Electronics – threaded spacers
• Oil and gas (extraction, processing, and distribution) – pins, gas fittings, retainers
• Machinery (packaging, filling, etc.) – pins, shafts, sleeves, and rods for mechanisms, fluid dispensing apparatus

Your Source for Precision Turned Parts

As part of our precision machining services, we undertake Swiss screw machining for customers in a diverse set of industries. If yours wasn’t listed above, don’t discount Swiss machining: part geometry dictates whether the process offers advantages. Contact us to find out.