Swiss Screw Machining
Swiss screw machining feeds bar stock through a guide bushing so cutting happens right next to the support, holding tight tolerances on slender parts.
- Part
- Cutting
- Revised
- 2026-08-11
At a glance
- Family
- Mechanical
- Typical tolerances
- ±0.0005 in (±0.013 mm) routine; ±0.0002 in (±0.005 mm) achievable on diameters; ±0.001 in (±0.025 mm) on lengths
- Surface finish
- 32 µin Ra (0.8 µm) typical; 16 µin (0.4 µm) achievable with finishing tools
- Typical volumes
- 500–1,000,000+ parts
- Lead time
- 2–4 weeks for first articles including setup; production releases in days once the setup is proven
- Materials
- Metal, Plastic
What it is
Swiss screw machining — properly, Swiss-type or sliding-headstock turning — feeds bar stock through a carbide guide bushing and cuts immediately in front of it. Because the unsupported length between the support and the tool never changes, a slender part does not deflect no matter how long it becomes, and diameters hold ±0.0002 in (±0.005 mm) on parts that a conventional lathe could not hold round.
Bar capacity runs roughly 0.020–1.5 in (0.5–38 mm), with 20 mm and 32 mm class machines covering most work. Several tool groups cut at once, a sub-spindle finishes the back end, and the machine runs unattended off a bar feeder, so cycle times fall to well under a minute and volumes of 500 to several million are normal.
It is the process behind bone screws, contact pins, needle hubs, fuel injector components, watch parts and connector shells — small, long, tight-tolerance turned parts made in quantity.
How it works
- Bar preparation. The guide bushing rides directly on the bar OD, so stock must be straight and held to a tight, consistent diameter — centerless-ground bar is normal for close-tolerance work. Poor bar quality shows up directly as diameter variation on the finished part.
- Guide bushing setup. Bushing clearance is set to a few ten-thousandths of an inch over the bar diameter, roughly 0.0002–0.0005 in (5–13 µm). Too tight and the bar galls and seizes; too loose and the accuracy advantage disappears.
- Sliding headstock motion. The headstock feeds the bar along Z while the tool holds a fixed Z position. The profile is generated by coordinating that feed with the tool's X motion, which is why a long slender diameter comes out straight instead of tapered.
- Simultaneous cutting. Gang tools, back-working tools and live tools engage at the same time on different features, so the cycle is the longest single operation rather than the sum of them.
- Live-tool operations. Cross-holes, flats, slots and thread milling are done in-cycle with driven tools; thread whirling cuts deep single-lead threads such as bone screw profiles in one pass.
- Sub-spindle pickoff. The sub-spindle grips the finished front end, the part is cut off, and back-end facing, drilling, chamfering and tapping happen while the main spindle already starts the next part.
- Unattended running. Straight cutting oil, often delivered through the tool, controls chips in small deep holes. Parts drop into a catcher or conveyor and the bar feeder reloads, allowing lights-out production.
Design guidelines
Play to the slenderness advantage
Swiss earns its rate on parts with a length-to-diameter ratio above about 3:1, and handles 20:1 and beyond. A short, stubby part with a large diameter is cheaper on a conventional chucker lathe.
Respect the headstock stroke
Tooling reaches only a limited length past the bushing before the headstock must retract and re-grip. Usable stroke is commonly 4–12 in (100–300 mm) depending on machine class; parts longer than that need a re-grip, which leaves a witness and introduces a tolerance step at that point in the length.
Minimum diameters and features
Turned diameters down to about 0.010 in (0.25 mm) and cross-holes of similar size are routine. Wall thickness on small turned tubes should stay at or above 0.010 in (0.25 mm). These numbers are an order of magnitude finer than conventional turning because the support is right at the cut.
Use free-machining bar wherever you can
303 stainless, C360 brass, 12L14 steel and 2011 aluminum run far faster and give better finish and chip control than 304, 316 or titanium. Since the process is priced by the second, alloy choice moves the part price more than geometry does.
Threads
Rolled and whirled threads are stronger and faster than single-point threading on small diameters. Use standard sizes from the thread size chart and tap drill chart; a custom pitch means a custom tool for a part that may run in the millions.
Tolerance and finish
Call out ±0.0005 in (±0.013 mm) as the general tolerance and reserve ±0.0002 in (±0.005 mm) for the diameters that mate. Lengths hold looser than diameters, typically ±0.001 in (±0.025 mm). Finish is 32 µin Ra (0.8 µm) typical and 16 µin (0.4 µm) achievable (surface finish chart).
| Material | Suitability | Watch for |
|---|---|---|
| 303 stainless | Excellent | The default Swiss stainless; best chip control |
| C360 brass | Excellent | Fastest cycles, best finish |
| 12L14 / 1215 steel | Excellent | Free-cutting; not for welded or plated-critical parts |
| 316 / 316L stainless | Good | Slower and gummier than 303; standard for implants |
| Ti-6Al-4V, nitinol | Difficult | Low speeds, sharp tools, high tool cost per part |
| 2011 / 6061 aluminum | Excellent | 2011 chips better; 6061 makes stringy chips |
| PEEK, acetal, PTFE | Good | Low cutting forces; support and coolant control matter |
| Feature | Recommended | Limit | Why |
|---|---|---|---|
| Length : diameter | 3:1 and up | 20:1+ | Below 3:1 a chucker is cheaper |
| Bar diameter | 0.062–1.25 in (1.6–32 mm) | 0.020–1.5 in (0.5–38 mm) | Machine bar capacity |
| Minimum turned diameter | 0.020 in (0.5 mm) | 0.010 in (0.25 mm) | Tool pressure vs part stiffness |
| Tube wall thickness | 0.020 in (0.5 mm) | 0.010 in (0.25 mm) | Collapse under tool pressure |
| Part length per grip | Within machine stroke | 4–12 in (100–300 mm) | Re-grip adds a witness line |
| General tolerance | ±0.0005 in (±0.013 mm) | ±0.0002 in (±0.005 mm) | Reserve the tight band for mating features |
Cost drivers
Swiss work is priced per second of cycle plus a substantial one-time setup, so the economics invert compared with prototype machining: setup is large, per-part cost is small, and quantity decides everything.
Setup. A Swiss job may use a dozen or more tools, all of which must be set, offset and proven out. That setup is charged once, which is why first articles feel expensive and the tenth thousand part feels almost free.
Cycle time and tool count. Every feature that cannot be overlapped with another adds directly to the cycle. Features that can be cut simultaneously with existing tool groups are nearly free.
Material. Free-machining alloys cut faster and last longer on tooling; 316, titanium and nitinol multiply both cycle time and tool consumption. Bar stock must also be precision-ground for close work, which costs more per pound than mill-run bar.
Secondary operations. Deburring, passivation, plating and cleaning on very small parts can rival machining cost, and handling millions of tiny parts is not trivial.
Four ways to take cost out:
- Get above a few thousand pieces before choosing Swiss — below that, CNC turning absorbs the setup better.
- Specify 303 rather than 304, and 12L14 rather than 1018, wherever corrosion and weldability allow.
- Keep the part within one headstock grip so no re-grip witness or tolerance step is needed.
- Apply ±0.0002 in (±0.005 mm) only to mating diameters and leave everything else at ±0.0005 in (±0.013 mm).
Questions
6 questionsWhat tolerance can Swiss screw machining hold?
±0.0005 in (±0.013 mm) is routine as a general tolerance and ±0.0002 in (±0.005 mm) is achievable on diameters. Lengths hold looser, typically ±0.001 in (±0.025 mm). The accuracy comes from the guide bushing supporting the bar immediately behind the cut, so the unsupported length never grows as the part gets longer.
What is the difference between Swiss machining and CNC turning?
On a conventional lathe the tool moves along a stationary rotating part held only at the chuck, so a long slender part deflects. On a Swiss machine the headstock slides and feeds the bar through a guide bushing, and cutting happens right at that support. The practical result is that Swiss handles length-to-diameter ratios of 20:1 and beyond while chuck turning is limited to about 3:1 unsupported.
What size parts can Swiss screw machines make?
Bar capacity is roughly 0.020–1.5 in (0.5–38 mm) in diameter, with 20 mm and 32 mm class machines covering the bulk of production. Turned diameters down to about 0.010 in (0.25 mm) are routine. Part length per grip is limited by headstock stroke, commonly 4–12 in (100–300 mm) depending on machine class.
What is the minimum volume for Swiss screw machining?
There is no hard minimum, but the setup involves a dozen or more tools that must all be set and proven, and that cost is charged once. Below roughly a few thousand pieces the setup dominates and conventional CNC turning is usually cheaper; above it, cycle times measured in seconds make Swiss the low-cost option.
Which materials run best on a Swiss machine?
Free-machining grades: 303 stainless, C360 brass, 12L14 steel and 2011 aluminum give the fastest cycles, best chip control and longest tool life. 316L, titanium and nitinol all run but multiply both cycle time and tool consumption, which matters because the part is priced per second of cycle.
Why does bar stock quality matter so much on Swiss machines?
The guide bushing rides directly on the bar outside diameter with only about 0.0002–0.0005 in (5–13 µm) of clearance. Any variation in bar diameter or straightness translates into diameter variation on the finished part, or into galling and seizure if the bar is oversize. Centerless-ground bar is standard for close-tolerance work.