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When misalignment between a servo motor and a lead screw causes vibration, lost steps, or premature bearing wear, the coupling is almost always the culprit. Engineers and CNC builders who demand repeatable positioning accuracy need a coupling that eliminates backlash entirely while still absorbing the angular and axial misalignment that real-world assemblies produce. This D39 double diaphragm flexible shaft coupler is engineered for exactly that application.
Each coupler consists of two precision-machined aluminum alloy hubs joined by a dual stainless-steel diaphragm pack. The outer diameter is 39 mm (≈1.54 in) and the overall length is 49 mm (≈1.93 in). Bore diameters span 8–19 mm (≈0.31–0.75 in) on both sides, with same-bore and mixed-bore configurations available to match your specific shaft pairing. Set screws secure each hub to its shaft.
Typical use cases include CNC router Z-axis drives where axial stiffness prevents tool chatter, servo-driven ball screw assemblies on milling machines and laser cutters, and rotary encoder coupling on precision measurement rigs where zero-backlash transmission is non-negotiable.
| Coupling Type | Double Diaphragm Flexible |
|---|---|
| Outer Diameter (D) | 39 mm (≈1.54 in) |
| Overall Length (L) | 49 mm (≈1.93 in) |
| Bore Diameter Range (φd1 / φd2) | 8–19 mm (≈0.31–0.75 in) |
| Hub Material | Aluminum Alloy |
| Flexible Element Material | Stainless Steel Diaphragm |
| Clamping Method | Set Screw |
| Backlash | Zero |
| Misalignment Compensation | Angular & Axial |
| Quantity per Order | See variant options |
| Weight (per piece) | See variant options |
Measure the shaft diameter of your motor (φd1) and the shaft diameter of your lead screw or driven component (φd2) with a digital caliper. Select the variant whose φd1 × φd2 combination matches your measurements. If both shafts are the same diameter, choose a same-bore variant (e.g., 10 mm × 10 mm). If they differ, choose the appropriate mixed-bore variant (e.g., 8 mm × 12 mm).
The double diaphragm design is suited for servo and stepper motor applications in the light-to-medium duty range, typically up to the torque ratings of NEMA 17–34 motors. For exact torque figures for your specific bore and speed combination, contact us to confirm before ordering for high-load applications.
Yes. The flexible diaphragm element is stainless steel, which provides good resistance to moisture and mild chemical exposure. The aluminum alloy hubs are naturally oxide-coated. For highly corrosive environments (salt spray, strong acids), additional protective measures may be needed.
NEMA 23 motors typically have 6.35 mm or 8 mm output shafts. This coupler's bore range starts at 8 mm, so it is compatible with standard 8 mm NEMA 23 shafts. Verify your motor's exact shaft diameter in its datasheet before ordering.
A single diaphragm coupler compensates primarily for angular misalignment. A double diaphragm coupler adds a second flexible element, which also accommodates axial (end-play) misalignment while maintaining higher torsional stiffness and zero backlash. This makes the double diaphragm design preferable for precision CNC and servo applications where both misalignment types are present.
Slide each hub onto its respective shaft, aligning the set-screw hole with a flat on the shaft if present. Bring the shafts into alignment as closely as possible, then tighten the set screws with the appropriate hex key to the recommended torque for the screw size. Avoid over-tightening, which can deform the bore. Re-check alignment after initial run-in.
Order 1 piece for a single-axis repair or prototype build. Choose 3 pieces for a 3-axis CNC machine (X, Y, Z) in one order. The 5-piece pack is ideal for multi-axis machines or when you want spare couplers on hand for maintenance. Multi-pack pricing offers a lower per-unit cost compared to single-piece orders.
