Starrag Bumotec S191

$600,000 - $950,000 Updated 2026-03-16

Key Specifications

Tool Capacity

Up to 48 tools

Accuracy

±0.002 mm (±0.00008 in)

Repeatability

±0.001 mm (±0.00004 in)

bar capacity

32 mm diameter (51 mm optional)

chuck diameter max

100 mm (3.9 in)

main spindle speed

12,000 RPM

Overview

The Starrag Bumotec S191 is a high-precision multi-technology machining center from Starrag's Swiss-based Bumotec brand, engineered for complete machining of complex small parts in medical, watchmaking, jewelry, and precision instrument sectors. It combines turning, milling, drilling, grinding, and gear-cutting operations in a single automated setup — the defining characteristic of the Bumotec philosophy — to deliver finished parts from bar stock without secondary operations.

The S191 works from bar stock up to 32 mm in diameter (51 mm with bar loader) and accommodates chuck parts up to 100 mm diameter. The main spindle delivers up to 12,000 RPM with a C-axis for synchronized operations, while the sub-spindle enables complete backworking. The milling spindle operates independently and provides the precision high-speed cutting capability needed for fine watchmaking features and intricate medical implant geometries.

A key differentiator of the S191 versus the heavier S191H is its configuration flexibility: the machine can be set up for tombstone-style multi-part fixturing, bar-fed automatic production, or chuck work depending on the part family. The Bumotec proprietary automation interface integrates with bar feeders from LNS and others. Linear encoders on all axes provide direct position feedback for exceptional accuracy: positioning accuracy of ±0.002 mm (±0.00008 in) and repeatability of ±0.001 mm (±0.00004 in).

The machine runs on Siemens SINUMERIK 840D sl, with Bumotec's proprietary HMI overlay simplifying the complex multi-technology operation for operators. Competitors include the Willemin-Macodel 508MT and INDEX R200. New S191 machines price between $600,000 and $950,000 depending on configuration and automation accessories.

Full Specifications

Parameter	Value
Bar Capacity	32 mm diameter (51 mm optional)
Chuck Diameter Max	100 mm (3.9 in)
Main Spindle Speed	12,000 RPM
Sub Spindle Speed	10,000 RPM
Milling Spindle Speed	36,000 RPM
Spindle Taper Milling	HSK-E32
C Axis	Main and sub spindle synchronized
Y Axis Travel	±50 mm (±2.0 in)
Tool Capacity	Up to 48 tools
Positioning Accuracy	±0.002 mm (±0.00008 in)
Repeatability	±0.001 mm (±0.00004 in)
Linear Encoders	Direct-scale on all axes
CNC Control	Siemens SINUMERIK 840D sl
Operations	Turning, milling, drilling, grinding, gear-cutting

Strengths & Limitations

Strengths

Complete part machining from bar stock in a single setup eliminates re-chucking errors and secondary operations, critical for medical implant dimensional integrity
36,000 RPM milling spindle enables ultra-fine surface finishes and micro-feature machining required in watchmaking and precision instrument work
Direct linear encoders on all axes provide true position feedback, achieving ±0.001 mm repeatability that few multi-technology machines can match
Synchronized main and sub-spindle C-axis enables true 5-axis simultaneous machining of back-face features without re-fixturing
Swiss Bumotec engineering heritage brings over 50 years of expertise in medical and watchmaking precision that informs every design decision
Siemens 840D sl with Bumotec HMI overlay reduces programming complexity for multi-technology operations, making setup accessible to skilled machinists

Limitations

32 mm bar capacity limits the machine to small-diameter workpieces; for parts larger than 100 mm diameter, the S191 is not suitable
Extremely high precision demands equally precise tooling, workholding, and thermal environment — ambient temperature control is often required
Programming complexity for simultaneous multi-technology operations (turning + milling + grinding) requires highly skilled setup technicians
Price above $600,000 puts the S191 out of reach for general job shops; ROI depends on high-value small-part production volume
Tool capacity of 48 is relatively modest for complex programs requiring many specialized tools across multiple operations

Best For

Medical device manufacturers producing orthopedic implants, surgical instruments, and dental components where complete machining accuracy and traceability are mandatory Swiss watchmakers and horological component suppliers machining movement parts, cases, and assemblies to micron-level precision from bar stock Aerospace fastener and precision fitting manufacturers producing complex small parts requiring turning, milling, and thread-cutting in one operation Precision instrument makers producing optical, measurement, and scientific equipment components with complex geometries and fine surface requirements Job shops specializing in high-value, low-volume precision parts where eliminating secondary operations dramatically improves delivery time and accuracy

Frequently Asked Questions

01 What is the difference between the Bumotec S191 and S191H?

The S191H is a heavier, more powerful variant of the S191 designed for harder materials and larger parts. The S191 prioritizes ultra-high precision and speed for small parts in medical, watchmaking, and instrument sectors, while the S191H adds greater structural rigidity and torque for harder aerospace alloys and slightly larger workpieces. Both share the Bumotec multi-technology philosophy of complete part machining in one setup.

02 Can the Bumotec S191 machine watch components?

Yes — watchmaking is a primary application. The S191's 36,000 RPM milling spindle, direct linear encoders, and ±0.001 mm repeatability make it capable of producing movement blanks, bridges, plates, jewel holes, and decorative surface features to horological standards. The machine's thermal stability and vibration damping are engineered with this level of precision in mind.

03 What materials can the S191 machine?

The S191 handles the full range of precision engineering materials: stainless steels (316L, 17-4PH), titanium alloys (Grade 5, Grade 23), cobalt-chrome for medical implants, brass and copper alloys for watchmaking, aluminum alloys, plastics, and hardened steels up to 60+ HRC with appropriate grinding operations. Its versatility across materials is central to the Bumotec multi-technology concept.

04 Does the S191 require a temperature-controlled room?

For maximum accuracy at ±0.001 mm repeatability, a temperature-stable environment (±1°C ideally) is recommended. Starrag integrates temperature compensation into the Siemens control, but shops requiring consistent micron-level results will benefit from controlling ambient temperature. Medical and watchmaking facilities typically already maintain ISO Class 7 or better cleanroom conditions that satisfy this requirement.

05 How does the S191 compare to a Swiss-type lathe for small parts?

A Swiss-type lathe (e.g., Citizen Cincom, Tornos Sigma) excels at high-volume production of long, slender turned parts with simpler geometries. The Bumotec S191 adds full 5-axis milling, grinding, and gear-cutting capability in the same setup — making it far more capable for complex 3D geometries. For parts requiring only turning and simple milling, a Swiss lathe is faster and cheaper; for complex multi-operation parts with tight tolerances, the S191 eliminates multiple machines and re-chucking errors.