Thin-Wall Concentric
Hollow Shafts

A hollow shaft is a shaft with a through-bore or blind bore along its central axis. The hollow design reduces weight (critical for robot joints and aerospace), allows routing of cables, pneumatic lines, or coolant through the shaft centre, and enables a through-spindle design for machine tools. Hollow shafts require careful design to avoid thin-wall distortion during machining and heat treatment.

Practical minimum wall thickness: 1.5 mm for steel and stainless; 2.0 mm for aluminium and titanium. Below these limits, the shaft can distort during machining (due to clamping pressure) and during heat treatment (due to thermal gradients). For thinner walls, consider electroless nickel or hard chrome on a thicker shaft rather than machining a very thin-wall hollow shaft. HXC flags thin-wall concerns in the DFM review.

HXC turns both OD and bore in a single 5-axis turning-milling setup without rechucking — this eliminates the setup error of a two-operation approach. Bore and OD are turned to grinding stock, then the OD is cylindrically ground using the bore as the datum (between centres or in a precision collet). Achieves OD-to-bore concentricity ≤ 0.003 mm TIR.

A hollow shaft of the same OD and length as a solid shaft, with bore = 70% of OD, retains approximately 76% of the bending stiffness while reducing mass by approximately 49%. For robot joint applications where rotational inertia dominates performance, hollow shafts are a major design advantage. Titanium hollow shafts offer the best strength-to-weight ratio for demanding aerospace applications.

Prototype (1–5 pcs, turned + 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.

42CrMo4 (induction hardened) for gearbox input and industrial. 20CrMnTi (carburized) for maximum surface fatigue. SUS303/316L stainless for food, pharma, marine. Al 6061/7075 hard-anodized for EV rotor and lightweight robot shafts. Ti Grade 5 for aerospace/medical. PEEK/POM for sterilizable or self-lubricating applications.

Standard ground OD: Ra 0.4 µm. Precision bearing seats: Ra 0.2 µm. Mirror finish for seals: Ra 0.1 µm. Bore: Ra 0.8 µm honed, Ra 0.4 µm on request. All measured by contact profilometer and reported.

Yes — keyways, splines, threads, cross-holes, oil ports, flats, and tapers are all machined in the same 5-axis turning-milling setup, ensuring concentricity between all features within 0.003 mm TIR.

Yes — HXC regularly machines hollow shafts with radial cross-holes, oil distribution ports, keyways, splines, and threaded ends in the same 5-axis setup. Cross-holes intersecting the bore must be deburred carefully — HXC uses precision deburring tools and verifies the bore is clear before shipment. Specify the cross-hole size, position, and any sealing requirements on the drawing.