Runout-Limited
Encoder Shafts

An encoder shaft (or encoder stub shaft) is a precision-ground short shaft section specifically designed to mate with a rotary encoder — optical, magnetic, or capacitive. The encoder reads the shaft rotation and converts it to a position or velocity signal. Any runout in the shaft directly adds to the encoder error, so runout tolerances are tighter than for a standard motor shaft: ≤ 0.003 mm TIR is standard for optical encoders, ≤ 0.001 mm for the highest-accuracy capacitive types.

Runout directly adds to encoder position error. If the encoder disk or magnet is mounted on a shaft with 0.010 mm runout, the encoder output will contain a once-per-revolution sinusoidal position error proportional to the runout — in a high-resolution encoder (e.g., 2,048 counts/rev), a 0.010 mm runout on a 10 mm shaft can produce a position error of several counts per revolution. This is why encoder shaft specifications use h5 tolerance and ≤ 0.003 mm runout where standard motor shafts use k5 and ≤ 0.010 mm.

Optical encoders with clamping hubs: shaft OD h5 (slight clearance), the encoder clamped by set-screw or split-clamp. Encoders with press-fit disk hubs: shaft OD p5 or r5 (slight interference). Encoders with adhesive-bonded disk: shaft OD h6 (clearance). The encoder manufacturer's assembly specification defines the required shaft OD tolerance — always check the datasheet. HXC grinds encoder shafts to any of these tolerance classes.

Yes — the most compact design is a motor shaft with an integrated encoder seat at the rear end: the motor bearing journal at one end (k5 fit), the rotor fit in the middle, and the encoder seat at the rear (h5, Ra 0.2 µm). All features in one 5-axis setup ensures concentricity between the motor bearings and encoder seat within 0.003 mm — critical for servo feedback accuracy.

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.

SUS303 (free-machining stainless): standard for servo and robot encoder shafts. 42CrMo4 (induction hardened) for CNC and heavy machinery. Al 6061-T6 (hard anodized) for cobot and lightweight. SUS316L (passivated) for medical and food. Ti Grade 5 for aerospace and high-precision instruments where minimum mass is critical.

Standard ground encoder seat: Ra 0.2 µm. Press-fit disk seat: Ra 0.1 µm (mirror lapped). Bearing journal: Ra 0.4 µm. All measured by contact profilometer and reported on the inspection certificate alongside the Talyrond runout trace.

Yes — D-flats, set-screw flats, keyways, threads, motor bearing journals, encoder seats, and cable cross-holes are all machined in the same 5-axis turning-milling setup, ensuring concentricity between motor bearings and encoder seat within 0.003 mm TIR.