RP6 Series Setscrew Oldham Coupling — aluminium alloy body, zero backlash, high torsional stiffness. Rated torque 0.7–80 N·m, max speed 9,000 rpm, radial misalignment up to 3.8 mm, angular tolerance 3°. 8 sizes (RP6-16 to RP6-70), metric and inch bores available. Stocked and shipped globally by RP.
The RP6 Series Setscrew Type Oldham Coupling is a compact, aluminium alloy three-piece flexible coupling engineered for precision servo, CNC, and encoder drive applications where zero backlash, high torsional stiffness, and the ability to accommodate both parallel and angular shaft misalignment are all required. With rated torque from 0.7 to 80 N·m, maximum speeds up to 9,000 rpm, and radial misalignment compensation up to 3.8 mm, the RP6 series covers the majority of small-to-medium precision drive coupling requirements in precision automation, robotics, and motion control applications.
Close-tolerance tongue-and-slot interface eliminates lost motion between input and output shafts, making the RP6 suitable for closed-loop servo positioning and encoder feedback systems.
Static torsional stiffness from 29 to 1,600 N·m/rad across the size range. High stiffness minimises angular lag in servo applications and preserves dynamic positioning accuracy during acceleration and deceleration cycles.
Accommodates up to 3.8 mm radial offset and 3.0° angular misalignment, significantly greater than bellows or disc couplings of similar size, reducing installation precision requirements on motor mounts and bearing housings.
The polymer intermediate disc provides electrical isolation between the two coupled shafts, breaking stray current paths that would otherwise damage encoder bearings, servo motor windings, and adjacent electronic components.
Setscrew (grub screw) hub retention allows rapid installation with a standard hex key. No special tools required. Compact envelope and low mass minimise the reflected inertia seen by servo drives.
Aluminium alloy hubs with natural anodising or optional hard-coat surface treatment resist oxidation and mild chemical exposure, suitable for automation and food-adjacent environments without the weight penalty of stainless steel.
An Oldham coupling is a three-piece flexible mechanical coupling designed to transmit rotary motion between two parallel shafts that are laterally offset from one another. The assembly comprises two outer hubs — each bored and fixed to one of the rotating shafts — and a central intermediate disc (the slider) with perpendicular tongue slots on each face that engage corresponding tongues on each hub. As the assembly rotates, the intermediate disc slides within the hub slots to continuously compensate for any radial (parallel) offset between the two shaft centrelines, while transmitting torque with a constant 1:1 velocity ratio.
The engineering problem the Oldham coupling resolves is intrinsic to real-world machinery: perfect shaft alignment is rarely achieved or maintained. Motor mount tolerances, thermal expansion, bearing wear, and cumulative assembly variation all introduce some degree of offset between connected shafts. A rigid coupling transmits this offset as a bending moment directly into shaft bearings and seals, accelerating wear and causing premature failure. An Oldham coupling intercepts that offset kinematically at the floating intermediate disc, keeping the lateral force path clean and bearing loads predictable.
What distinguishes the Oldham design from elastomeric couplings — such as jaw or spider-type units — is its essentially rigid torque path and zero-backlash characteristic. There is no elastic element to fatigue, creep, or change stiffness with temperature. The intermediate disc material handles the sliding compensation function without introducing torsional compliance or angular velocity variation.
Each aluminium alloy hub carries a single raised rectangular tongue machined to close tolerances on its face. The intermediate disc carries two perpendicular slots — one on each face — that accept these tongues as a precision sliding fit. When the drive hub rotates, its tongue pushes the disc linearly in one direction. The disc simultaneously slides in the perpendicular direction relative to the driven hub. The net output is pure torque transfer at a constant 1:1 velocity ratio.
For the RP6 series, radial misalignment compensation ranges from 1.0 mm on the RP6-16 up to 3.8 mm on the RP6-63 and RP6-70 sizes. Angular misalignment tolerance is 3.0° across all eight sizes — a notably high angular tolerance for a zero-backlash coupling, and a feature that significantly reduces installation precision requirements. Maximum operating speeds range from 9,000 rpm (RP6-16) down to 2,300 rpm (RP6-70).
In servo positioning systems, encoders, and CNC auxiliary drives, the zero-backlash characteristic of the RP6 is critical. Any elastic windup or lost motion in the torque path appears directly as a positioning error in closed-loop control. The RP6's rigid tongue-and-slot torque path maintains a fixed angular relationship between motor shaft and load shaft, preserving the accuracy of the position feedback loop. The low rotational inertia of the aluminium alloy assembly — as low as 3.0 × 10⁻⁷ kg·m² on the RP6-16 — also minimises reflected inertia at the servo drive, enabling faster current and velocity loop response times.
All published dimensional and performance data for the RP6 series are listed in the tables below. Note that moment of inertia and mass figures are based on the maximum shaft bore for each size.
RP6 — [Outside Diameter] — [d1 Bore][d2 Bore]
Example: RP6-25-0810 = RP6 Series, 25 mm outside diameter, d1 bore 8 mm, d2 bore 10 mm. The outside diameter determines the frame size. Specify the d1 and d2 bore diameters to match your drive and driven shaft sizes.
| Model | Bore d1, d2 (mm) | OD (mm) | L (mm) | F (mm) | L1 (mm) | M (Setscrew) | Wrench Torque (N·m) |
|---|---|---|---|---|---|---|---|
| RP6-16 | 4, 5, 6 | 16 | 18 | 3.5 | 7 | M3 | 0.7 |
| RP6-20 | 6, 6.35, 8 | 20 | 23 | 4.5 | 9 | M4 | 1.7 |
| RP6-25 | 6.35, 8, 9.525, 10 | 25 | 28 | 5.5 | 11 | M5 | 4.0 |
| RP6-32 | 8, 9, 9.525, 10, 11, 12, 14 | 32 | 33 | 6.5 | 13 | M6 | 7.0 |
| RP6-40 | 12, 14, 15, 16 | 40 | 35 | 7.0 | 14 | M6 | 7.0 |
| RP6-50 | 14, 15, 16, 18, 19, 20 | 50 | 38 | 8.5 | 17 | M8 | 15 |
| RP6-63 | 16, 18, 19, 20, 24, 25 | 63 | 47 | 10.5 | 21 | M10 | 30 |
| RP6-70 | 24, 25, 28, 30, 32, 35 | 70 | 59 | 12.5 | 26 | M10 | 32 |
Note: Moment of inertia and mass figures are based on the maximum shaft bore for each size.
| Model | Rated Torque (N·m) | Max Torque (N·m) | Max Speed (rpm) | Moment of Inertia (kg·m²) | Static Torsional Stiffness (N·m/rad) | Radial Misalignment (mm) | Angular Misalignment (°) | Mass (g) |
|---|---|---|---|---|---|---|---|---|
| RP6-16 | 0.7 | 1.4 | 9,000 | 3.0 x 10⁻⁷ | 29 | 1.0 | 3.0 | 6 |
| RP6-20 | 1.6 | 3.2 | 7,400 | 9.0 x 10⁻⁷ | 58 | 1.4 | 3.0 | 14 |
| RP6-25 | 3.0 | 6 | 5,800 | 2.8 x 10⁻⁶ | 125 | 1.9 | 3.0 | 24 |
| RP6-32 | 5.5 | 11 | 4,700 | 8.9 x 10⁻⁵ | 260 | 2.4 | 3.0 | 46 |
| RP6-40 | 9.0 | 18 | 3,600 | 2.1 x 10⁻⁴ | 505 | 2.8 | 3.0 | 80 |
| RP6-50 | 19.0 | 38 | 3,000 | 6.0 x 10⁻⁵ | 780 | 3.3 | 3.0 | 144 |
| RP6-63 | 33 | 66 | 2,400 | 2.1 x 10⁻⁴ | 1,200 | 3.8 | 3.0 | 318 |
| RP6-70 | 80 | 160 | 2,300 | 1.7 x 10⁻⁴ | 1,600 | 3.8 | 3.0 | 456 |
The RP6 series is supplied with aluminium alloy hubs as standard. Aluminium delivers an excellent strength-to-weight ratio, keeping coupling inertia to a minimum — essential for high-speed servo and encoder applications where reflected inertia directly affects drive tuning. Anodising provides corrosion resistance and surface hardness suitable for most industrial environments.
Lightweight and electrically insulating. The standard intermediate disc material for most RP6 applications. Provides electrical isolation between drive and driven shafts that protects encoder bearings and servo electronics from stray currents. Self-lubricating properties minimise wear at the tongue-slot interfaces.
Higher rigidity and improved dimensional stability under sustained load compared to nylon. Specified for applications where maximum torsional stiffness is required or where the intermediate disc will be subjected to heavier cyclic loading. Lower moisture absorption than nylon ensures consistent tongue-slot clearance in humid environments. Available on request for RP6-32 and larger sizes.
Available on request for food processing, pharmaceutical, and marine applications where aluminium alloy is not suitable due to corrosive washdown environments or regulatory requirements. Grade 304 and 316 options available. Stainless steel hubs increase coupling mass and inertia versus aluminium equivalents; verify servo drive inertia ratio before specifying stainless in high-dynamic applications.
Need a higher torque coupling for your drive application? Browse the complete RP coupling range, including the WH Type and SL Type Oldham series covering torque requirements from light servo drives through to 63,000 N·m heavy industrial applications.
The table below compares the RP6 Series Setscrew Oldham Coupling against three coupling types frequently evaluated alongside it in precision drive and automation procurement.
| Parameter | RP6 Oldham (Setscrew) | Jaw Coupling | Bellows Coupling | Disc Coupling |
|---|---|---|---|---|
| Parallel Offset Compensation | Excellent (up to 3.8 mm) | Limited (0.1–0.5 mm) | Low (0.1–0.3 mm) | Very Low (<0.1 mm) |
| Angular Misalignment Tolerance | 3.0° (all sizes) | Moderate (1°–2°) | Good (1°–3°) | Low (0.5°–1°) |
| Backlash | Zero | Low–Moderate | Near Zero | Near Zero |
| Electrical Insulation | Yes (polymer disc) | Yes (spider) | No | No |
| Torsional Stiffness | High (29–1,600 N·m/rad) | Low–Moderate (spider material) | Very High | Very High |
| Max Speed | Up to 9,000 rpm | Up to 6,000 rpm | Up to 10,000+ rpm | Up to 10,000+ rpm |
| Installation | Simple — hex key setscrew | Simple — spider accessible | Moderate | More complex |
| Relative Cost | Low–Moderate | Low | High | High |
RP6 Series couplings are produced under an ISO 9001 certified quality management system with documented process controls for precision machining of hub bores, tongue profiles, and setscrew threads. Products comply with RoHS substance restrictions. CE conformity documentation and material test certificates are available for applications requiring formal compliance records.
Custom bore diameters not in the standard table, metric and imperial keyway profiles, alternative intermediate disc materials, stainless steel hubs, and custom surface treatments are all available. Minimum order quantity for custom specifications is 5 pieces. Lead time is typically 7–15 business days from drawing confirmation. For OEM volume requirements, contact us to discuss blanket order pricing and scheduled release programmes.
Standard in-stock orders dispatch within 2–3 business days. Standard products in original condition may be returned within 30 days. Custom-specification orders are subject to prior approval for return or exchange.
Ready to verify your coupling selection or request a sample? Contact the RP engineering and sales team — we typically respond within one business day with a confirmed recommendation and pricing.
Tell us your shaft diameters (d1 and d2), required OD frame size, and application torque and speed — we will verify your bore combination, intermediate disc material, and pricing within one business day.
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