Swiss Machining
Also: Swiss screw machining, Swiss-type turning, sliding headstock turning, Swiss lathe, Swiss turning, guide bushing lathe, Swiss CNC, Swiss-style lathe
Swiss machining turns small, long, precise parts from bar on a sliding-headstock lathe: the bar is supported at the cut, so 10:1 lengths hold ±0.005 mm.
193 shops tagged Swiss machining among 5,104 CNC machining companies in the Noramark directory
On a Swiss-type (sliding headstock) lathe the bar passes through a guide bushing that sits just ahead of the tools, and the headstock pushes the bar out through the bushing as the tools cut. The cut is always within a few millimeters of the support, so slender parts do not deflect and chatter. Gang tooling, back-working tools and a sub-spindle finish the part completely, with live tools for cross holes, slots and flats, and the machine runs from a bar feeder unattended for hours.
Swiss machines own the small end of turning: parts under about 32 mm (1-1/4") diameter, long parts with length ten or more times the diameter, diameters held to ±0.005 mm (±0.0002") and finishes of 0.4 µm Ra (16 µin) off the tool. Bone screws and implants, electrical pins and contacts, fluidic fittings, precision fasteners and instrument shafts are typical. Cycle times run from seconds to a few minutes, and runs from 500 to 500,000 pieces.
The bar has to run through the bushing, so it must be straight and ground to a close tolerance, which adds material cost. Setup for a complete part takes hours, so short runs cost more per piece than on a chucker lathe, and short fat parts gain nothing from the sliding headstock. Above the bar capacity the work goes to conventional CNC turning.
At a glance
| Typical tolerances | Standard ±0.013 mm (±0.0005") on diameters and ±0.025 mm (±0.001") on lengths; ±0.005 mm (±0.0002") on diameters with care, and ±0.0025 mm (±0.0001") on the best machines with temperature control and in-process gauging. Roundness and concentricity of 0.005 mm (0.0002") between features cut in one pass; back-worked features hold about 0.013 mm (0.0005") to the front. |
|---|---|
| Size limits | Bar capacity sets the limit: 20 mm (3/4") and 32 mm (1-1/4") machines are common and 38 mm (1-1/2") less so. Parts as small as 0.3 mm (0.012") diameter are routine at medical and electronics shops. Length per part follows the headstock stroke, typically 200-300 mm (8-12"), with longer parts by re-chucking. Bar comes in 3-4 m (10-12 ft) lengths. |
| Surface finish | As-turned 0.4-0.8 µm Ra (16-32 µin); 0.2 µm Ra (8 µin) with care on diameters in stainless, titanium and brass. Threads are single-pointed or thread-whirled; whirled bone-screw threads come off at about 0.4 µm Ra. Parts are usually tumbled, passivated or electropolished afterwards rather than ground. |
| Lead time | First articles in 2-4 weeks, because setup and tooling for a complete part take days; production in 4-8 weeks, with blanket orders released monthly. Ground bar in an unusual alloy or size can add 2-4 weeks. |
Typical of U.S. job shops; confirm with the shop for your part.
Materials
Stainless is the bread and butter: 303 and 416 for free cutting, 304 and 316 with good chip control, 17-4 PH and 440C for medical and aerospace hardware. Ti-6Al-4V for implants, C360 brass and beryllium copper for electrical contacts, 12L14 and 4140 for pins and shafts, and 6061 for lightweight fittings all run well. Delrin and PEEK turn cleanly for insulators and implant components; PTFE and UHMW are difficult because they deflect and smear. Any alloy must be available as centerless-ground, straightened bar in the needed diameter.
What drives the cost
- Cycle time: features and tool changes per part, and the cutting speed of the material
- Quantity: a Swiss setup takes hours, so under a few hundred pieces the setup dominates the unit price
- Bar stock: centerless-ground, straightened bar costs more than commercial bar, and the remnant is a larger share on small diameters
- Tolerances below ±0.005 mm (±0.0002") and finishes below 0.4 µm Ra
- Material: titanium, 17-4 and 440C cut slowly and wear tools; brass and 303 run fast
- Back-work, cross-drilling, thread whirling and deep drilling that add tool stations
- Validation for medical and aerospace: first article, PPAP, lot traceability and cleanliness
When to use it
- Turned parts under 32 mm (1-1/4") diameter, and especially under 10 mm (3/8")
- Long slender parts: length more than five to ten times the diameter
- Diameters and concentricity held to ±0.005 mm (±0.0002")
- Production quantities from 500 to hundreds of thousands, running unattended
- Medical screws and implants, electrical contacts and pins, fluidic fittings, precision fasteners and shafts
When not to
- Parts larger than the bar capacity, or short fat parts that a chucker lathe makes faster
- Prototypes and quantities under 100, where setup time swamps the run
- Geometry that is mostly milled with a little turning: a mill-turn or 5-axis machine is a better fit
- Materials that cannot be bought as straight, ground bar in the diameter needed
Design tips
- Design to a stock bar diameter so the largest OD is the bar; a part turned down from much larger stock wastes time and material.
- Swiss handles 10:1 length to diameter and more, but a long part still needs a plan for the back end: a sub-spindle pickoff or a support.
- Add a chamfer or radius to every edge; a burr on a 2 mm pin is a rejected part.
- Group tight tolerances on features cut in one pass; back-end features done on the sub-spindle hold looser to the front.
- Specify surface finish and roundness only where they matter, and say whether passivation or electropolish is required.
- For threads give the class and say whether cut, rolled or whirled matters; for medical threads reference the standard rather than drawing the form.
- Ask for price breaks at 500, 1,000 and 5,000 pieces; the process rewards volume.
Frequently asked questions
- What is Swiss machining?
- Turning on a sliding-headstock lathe, where the bar feeds through a guide bushing and is cut right next to the support. It was developed for watch parts and now makes small, long, precise turned parts for medical, electronics, aerospace and fluid-handling work, usually in volume.
- What size parts can a Swiss lathe make?
- Up to the bar capacity, commonly 20 or 32 mm (3/4 or 1-1/4") and occasionally 38 mm (1-1/2"), and down to about 0.3 mm (0.012") diameter. Length per part is typically 200-300 mm (8-12") per headstock stroke.
- Swiss machining or CNC turning?
- Swiss for small diameters, long slender shapes, ±0.005 mm (±0.0002") tolerances and runs of hundreds and up. Conventional CNC turning for larger diameters, short parts, and prototypes or small lots, because it sets up in minutes rather than hours.
- What tolerances can Swiss machining hold?
- ±0.013 mm (±0.0005") on diameters is standard, ±0.005 mm (±0.0002") is achievable with care, and the best shops hold ±0.0025 mm (±0.0001") with temperature control and in-process gauging. Lengths and back-worked features hold a little looser.
- Why does Swiss machining need ground bar stock?
- The bar slides through a guide bushing with only a few micrometres of clearance. Any variation in bar diameter or straightness shows up directly as size and runout error on the part, or seizes the bar in the bushing, so shops buy centerless-ground, straightened bar.
