Swiss-Type CNC Lathe Product

Overview

A Swiss-type CNC lathe machines small, long, slender parts directly from bar stock. Its defining feature is the combination of a Sliding Headstock that slides along the spindle axis and a Guide Bushing Unit fixed at the working zone. Instead of holding the bar at one end and bringing tools to it, the machine pushes the rotating bar through the Guide Bushing and does all cutting within about a millimetre of that support point. A part 100 mm long and 2 mm in diameter, which would deflect hopelessly on a conventional lathe, can be turned in one pass because the unsupported overhang at the tool never exceeds the bushing clearance.

The architecture originated in the Swiss watch industry in the 1870s (Jakob Schweizer's design for screw making in the Jura valley) and survives essentially unchanged in CNC form. Typical work today is medical bone screws, fuel injection components, electronic connector pins, and watch arbors — production runs of thousands of parts at diameters from 1 to 32 mm with tolerances of a few micrometres.

How it works

Bar stock 2-4 m long is loaded by an automatic magazine feeder through the Bar Feeder Interface. The bar passes through the hollow Main Spindle, is clamped by the Main Spindle Collet, and protrudes through the guide bushing into the working zone. The Built-In Spindle Motor spins the bar at up to 15,000 rpm; an integral Encoder gives full C-axis positioning so flats and cross-holes can be cut at indexed angles.

Turning works inverted relative to a conventional lathe: the Z feed comes from the headstock. The casting rides on Linear Guideway rails and a Ball Screw driven by a Servo Motor advances the bar past the tool at the programmed feed per revolution. The tools themselves sit on the Gang Tool Slide, a cross slide carrying six Turning Tool Holder positions in a row on the Gang Tool Plate. Selecting a tool is a fast X/Y positioning move of roughly 0.3 s rather than a turret index, which matters when cycle times are 20-60 seconds. The Live Tool Unit adds three rotating ER Collet Tool Spindle stations for cross-drilling, milling, and slotting while the C axis holds or indexes the bar.

The Guide Bushing itself is a carbide-lined split bushing, ground to the bar diameter plus a clearance of 5-10 µm and adjusted with the Bushing Adjusting Nut. In the rotary-bushing arrangement used here, the Bushing Drive Sleeve is belt-driven in synchronism with the spindle via a Drive Belt, so there is no relative rotation between bar and bushing to score ground stock. Bar straightness and diameter consistency (h9 or better, often centerless-ground) directly determine achievable accuracy, which is the main running cost penalty of the Swiss architecture.

Sub-spindle and backworking

Before cutoff, the Sub-Spindle Assembly advances, matches speed with the main spindle, and grips the part with the Sub-Spindle Collet. The cutoff tool then severs the part, which leaves with the sub-spindle for second-side operations against the Backworking Tool Post — back drilling, chamfering, threading — while the main spindle simultaneously starts the next part. The two-channel CNC Unit runs both processes in parallel with wait codes at the transfer. Finished parts are blown out by the Parts Ejector into a catcher, so the machine runs unattended until the bar magazine empties. The Interlock Switch signals end-of-bar; the remnant is ejected and the feeder loads the next bar in about 30 seconds.

Supporting systems

The machine sits on a ribbed Bed Casting of roughly two tonnes, levelled on six Leveling Foot mounts; thermal symmetry of the casting matters because a 1 °C gradient can move the cutting point several micrometres. Swiss machines almost universally run neat cutting oil rather than water emulsion: the Coolant and Chip System circulates about 200 L from the Cutting Oil Tank through a low-pressure flood circuit and a 7 MPa high-pressure circuit fed by twin Coolant Pump units, monitored by a Pressure Sensor. Oil gives better lubricity at the small chip loads involved and doubles as the guide bushing lubricant. Fine chips collect in the Chip Bin behind the interlocked Front Access Door.

Motion control runs through seven Servo Drive amplifiers in the electrical cabinet, with a Power Supply for 24 V logic and a bank of Relay switching for safety circuits. The operator works from the LCD Panel and Operator Panel; programs use two parallel part-program channels, one per spindle, a structure unique to multi-channel lathes.

Swiss versus fixed-headstock turning

The guide bushing buys rigidity but costs material: every part leaves a remnant of bar (150-300 mm) that cannot pass the bushing, and bar must be straight, ground stock. For short, large-diameter parts a fixed-headstock CNC Unit-controlled chucker is cheaper per piece. The Swiss layout wins decisively when length-to-diameter ratio exceeds about 3:1, when one-hit machining of complex small parts eliminates secondary operations, or when the lights-out economics of bar-fed running dominate.