Custom CNC Ground
Precision Spacers

A precision spacer (distance piece) is a short ring or tube ground to a precise axial length, used to establish a controlled gap or preload in a precision assembly. The most critical application is a bearing preload spacer — the spacer length determines the preload force on the bearing pair, so a ±0.005 mm tolerance on spacer length translates directly into controlled bearing preload.

In a preloaded bearing pair (angular contact or taper roller), the spacer between the inner races (or outer races) sets the axial preload. If the spacer is 0.010 mm too short, the bearing is 0.010 mm overpreloaded — increasing friction, heat, and fatigue. Too long: the bearing is underloaded, allowing ball skidding at high speed. Precision spacers ground to ±0.005 mm allow bearing preload to be controlled within the manufacturer's specified window.

Bearing preload spacers: face parallelism ≤ 0.003 mm — this ensures the preload force is applied uniformly around the bearing circumference rather than as a tilted force on one side. Optical bench spacers: ≤ 0.002 mm for interferometric applications. General assembly spacers: ≤ 0.005 mm is acceptable. HXC achieves face parallelism by double-face grinding both faces in a single setup.

Length is measured using a calibrated micrometer or CMM height gauge under controlled temperature (20°C ±0.5°C) on a surface plate. Face parallelism is measured by CMM scanning both faces. For bearing preload spacers where tolerance is ±0.005 mm, HXC sorts spacers into ±0.002 mm bins after grinding, so sets can be matched for exact preload requirements.

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 industrial and automotive. 20CrMnTi (carburized) for maximum surface fatigue. SUS303/316L stainless for food, pharma, marine. Al 6061/7075 hard-anodized for lightweight. 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. All measured by contact profilometer and reported on the inspection certificate.

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