5-Feature Integrated
Joint Shafts

A joint shaft is a compact precision shaft used as the pivot or rotation centre in a robot joint, wrist, or gimbal. Unlike a standard drive shaft that mainly transmits torque, a joint shaft must simultaneously serve as the bearing journal, the structural load path, and often as the torque transmission element — all in a very compact envelope. This combination of requirements in a small space makes joint shafts among the most complex shaft designs.

A typical 6-DOF robot wrist joint shaft includes: two bearing journal zones (for the inner and outer bearing races); a spline or polygon drive zone (connecting the joint to the harmonic drive or cycloid reducer output); an encoder seat (for joint angle feedback); cable routing cross-holes (for wiring through the joint); and a lightweight hollow bore (to reduce rotational inertia). HXC machines all these features in one 5-axis setup.

Al 7075-T6 (hard anodized): the standard for robot joint shafts where minimum inertia is critical — used in collaborative robots and lightweight arms. Ti Grade 5: for the highest strength-to-weight ratio in aerospace robot joints. SUS316L (passivated): for medical and surgical robot joints requiring sterilizability. 42CrMo4: for heavy industrial robot joints with high torque and impact loading.

Joint shaft rotational inertia directly affects robot acceleration, energy consumption, and cycle time. In a multi-axis robot, the contribution of joint shaft inertia to the total axis inertia seen by the servo motor is approximately (shaft inertia) × (gear ratio)². Using Al 7075 hollow joint shafts vs steel solid shafts can reduce axis inertia by 60–70%, allowing faster acceleration with the same motor — or smaller, lighter motors for the same performance. HXC calculates joint shaft inertia as part of the DFM review.

Prototype (1–5 pcs, turn-milled + ground): 4–7 days. Small batch (10–50 pcs): 7–12 days. Production (100–1,000 pcs): 10–16 days. Stainless or titanium: add 2–4 days. Rush production available.

Al 6061/7075-T6 hard-anodized for cobot and lightweight arms. Ti Grade 5 for aerospace/medical. SUS303/316L for surgical and food/pharma. 42CrMo4 (induction hardened) for heavy industrial. 20CrMnTi (carburized) for shock-loaded shoulder joints. PEEK for EMI/MRI-safe medical robots.

Standard ground bearing journal: Ra 0.4 µm. Encoder seat (h5 OD): Ra 0.2 µm. Mirror finish for seal contact: Ra 0.1 µm. All measured by contact profilometer and reported on the inspection certificate.

Yes — bearing journals, splines, encoder seats, cross-holes for cable routing, hollow bores, and threaded ends are all machined in the same 5-axis turn-mill setup, ensuring concentricity between all features within 0.005 mm TIR. This integration is the central value HXC offers for joint shafts.

Yes — a through-bore from one end to the other is the standard approach for cobot wrist and elbow joints to route servo cables, encoder cables, and pneumatic lines through the joint centre. Minimum wall thickness 1.5 mm for steel/stainless and 2.0 mm for aluminium. HXC adds radial cross-holes at the joint to route cables out where the next joint connects.