Studer S31
Key Specifications
Max Workpiece ⌀
Accuracy
center height
distance between centers
max workpiece weight
grinding wheel diameter
Overview
The Studer S31 is a universal cylindrical grinding machine from Fritz Studer AG (part of United Grinding Group) designed for the grinding of medium-sized workpieces in single-part and small batch production. It occupies the broad mid-range of Studer's product lineup — above the compact S11 and S21 but below the large-capacity S33 and S41 — targeting tool rooms, precision job shops, and manufacturing cells that need a versatile external and internal cylindrical grinder for workpieces up to 400 mm (15.7 in) diameter.
The S31 features Studer's StuderGuide hydrostatic guideways on all axes — a technology that provides oil film damping and near-zero stick-slip motion, enabling smooth grinding at very slow table speeds and precise infeed during fine finishing cycles. The workpiece rotation is driven by a high-speed frequency-controlled spindle reaching 800 RPM at the workhead. Grinding wheel spindle power is 7.5 kW with a 1A1 50 mm wide wheel as standard, accommodating both OD and form grinding configurations.
Internal grinding is handled through the S31's optional internal grinding attachment (ISM), which adds high-frequency grinding spindles (up to 150,000 RPM for small-diameter bores) mounted on the wheel spindle housing. The StuderWIN control with StuderGRIND software handles cylindrical, taper, radius, and form grinding cycles. The software includes a dressing cycle calculator, automatic sizing loop, and tool compensation that removes operator interpolation for complex profiles.
The S31 competes with the Toyoda GE4, Okuma GA26W, and Kellenberger 600 in the mid-range universal cylindrical grinder class. Studer's differentiation is the hydrostatic guideway system, Swiss manufacturing precision, and the depth of the StuderGRIND software package. Typical pricing runs $400,000–$700,000 depending on table length, internal grinding attachment, and measuring probe configuration.
Full Specifications
| Parameter | Value |
|---|---|
| Max Workpiece Diameter | 400 mm (15.7 in) between centers |
| Center Height | 175 mm (6.9 in) |
| Distance Between Centers | 650 mm (25.6 in) standard; 1000 mm (39.4 in) optional |
| Max Workpiece Weight | 80 kg (176 lb) between centers |
| Grinding Wheel Diameter | 500 mm (19.7 in) x 63 mm (2.5 in) |
| Grinding Spindle Power | 7.5 kW (10 hp) |
| Grinding Spindle Speed | 1,260–3,550 RPM (variable) |
| Workhead Speed | 1–800 RPM (variable) |
| Tailstock Spindle | MT 3 (Morse taper) |
| X Axis Infeed | 10 mm (0.394 in) minimum infeed 0.001 mm |
| Z Axis Traverse | 700 mm (27.6 in) |
| X Axis Resolution | 0.0001 mm (0.000004 in) |
| Z Axis Resolution | 0.001 mm (0.00004 in) |
| Positioning Accuracy | ±0.002 mm (±0.00008 in) |
| Roundness | 0.003 µm under controlled conditions |
| Guideway System | StuderGuide hydrostatic guideways (X and Z axes) |
| Machine Weight | 5,500 kg (12,125 lb) |
| CNC Control | Studer StuderWIN (Fanuc-based) with StuderGRIND software |
| Floor Space Required | approximately 3.2 m x 2.6 m |
| Electrical | 400 VAC 3-phase 50 Hz / 460 VAC 60 Hz |
Specifications sourced from studer.com — verified 2026-03-28
Strengths & Limitations
Strengths
- StuderGuide hydrostatic guideways on X and Z axes provide exceptional damping and smooth motion at very low traverse speeds essential for precision cylindrical grinding
- Optional internal grinding attachment (ISM) with high-frequency spindles enables both OD and ID grinding in a single setup on the same machine
- StuderGRIND software with dressing cycle calculator and automatic sizing loop reduces programming complexity and operator skill requirements for complex profiles
- Swiss manufacturing precision with roundness capability under 0.003 µm makes the S31 suitable for precision bearing races, gauges, and hydraulic valve components
- 400 mm maximum workpiece diameter covers the majority of precision cylindrical grinding applications encountered in aerospace, automotive, and tooling sectors
Limitations
- Price of $400K–$700K positions the S31 well above competing cylindrical grinders from Toyoda, Okuma, and Kellenberger at similar workpiece capacity
- Hydrostatic guideway system requires continuous oil supply and filtration — the maintenance and operational cost is higher than ball-screw linear guide machines
- 650 mm standard between-center distance limits shaft grinding to shorter workpieces; the 1000 mm option adds cost but is essential for longer shaft applications
Best For
Frequently Asked Questions
01
StuderGuide is Studer's proprietary hydrostatic guideway technology where a continuous pressurized oil film between the guideway surfaces provides load support and motion guidance. This eliminates metal-to-metal contact, providing near-zero stick-slip motion at any traverse speed, superior vibration damping compared to rolling element guides, and consistent guideway geometry over decades of service. Hydrostatic guideways are considered the gold standard for precision cylindrical grinding because they enable ultra-smooth infeeding during fine finishing cycles.
02
Yes. The S31 with the optional internal grinding attachment (ISM) can perform OD cylindrical grinding and ID bore grinding in a single machine setup. The ISM mounts a separate high-frequency spindle (up to 150,000 RPM for small bores) on the main wheel spindle housing. The control manages both the main spindle and the ISM spindle. This combined capability eliminates part transfers between OD and ID grinding machines, reducing setup time and maintaining concentricity between OD and ID features.
03
The S31 grinds all cylindrically grindable materials: hardened tool steel (58–65 HRC), carburized gear steel, cemented carbide, ceramics, tungsten carbide, and hardened stainless steels. CBN (cubic boron nitride) wheels are used for hardened steels and Inconel for optimal material removal and surface integrity. Diamond wheels are used for ceramics and carbide. Conventional aluminum oxide wheels are appropriate for softer steels and general OD grinding at lower accuracy requirements.
04
The S21 is Studer's compact cylindrical grinder for workpieces up to 250 mm diameter in a smaller footprint and at a lower price. The S31 handles up to 400 mm diameter with a longer between-center distance. The S33 is the large-capacity variant handling up to 400 mm diameter but with the standard 1500 mm between-center distance — better suited for longer shafts and production cylindrical grinding. The S31 is the 'universal' mid-range machine for single-part and small batch work across a wide range of part sizes.
05
Under optimal conditions (properly dressed CBN wheel, appropriate speeds and feeds, thermally stable environment), the S31 achieves Ra 0.1–0.2 µm in standard production. With fine-grit wheels (100+ mesh) and light spark-out passes, Ra 0.05–0.08 µm is achievable on hardened steel. Roundness error below 0.003 µm is achievable in controlled conditions, making the S31 suitable for precision bearings and hydraulic sealing surfaces. Surface finish targets depend on material, wheel specification, and dressing parameters.
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