Stainless Steel Stepped Bushing with Turn-Mill Machining and 0.01mm Bore to OD Concentricity for Precision Assemblies

A stepped bushing fits into a housing at one diameter and carries a shaft, pin or bearing at another. Buyers usually quote the bore and the outside diameters, but the dimension that decides whether the assembly works is the wall between them — the concentricity of bore to outside diameter, and the accumulated height of the steps. Off by 0.02 mm on wall and the shaft runs tight on one side; off by 0.03 mm on a step stack and the bushing does not seat flush in the housing.

We turn the bore and every outside step in one operation wherever the geometry allows, then finish the second end on the sub-spindle so both ends share one axis. Each step diameter and height is measured separately on the CMM, the bore is checked with an air gauge, and the report that ships with the parts lists the actual numbers rather than a pass stamp.

Wall thickness is quoted as a checkable number because it is what the assembly feels. If your drawing only gives bore and outside diameters, we calculate the wall from them and report the measured variation, so a fitting tolerance issue shows up on paper before it shows up at assembly.

• Material: SS303 (free machining, fine finish), SS304, SS316/316L (corrosion), SS416 (hardenable, magnetic), 17-4PH (high strength after aging), brass C36000, aluminium 6061.
• Geometry: 2 to 5 outside steps, stepped or straight bore, blind bore, counterbore, internal groove, O-ring groove, flange or collar, knurl band, hex or spanner flats, cross hole.
• Fit: press fit, slip fit, H7/H8 bore, h6/g6 outside diameter, or a fit defined by your measured mating part.
• Finish: passivation per ASTM A967, electropolish, bead blast, black oxide, nickel plating, or as-machined.
• Size: OD 4 mm to 120 mm, bore 1.5 mm to 100 mm, length 5 mm to 250 mm, wall from 0.5 mm.
• Input: STEP, IGES, DXF, PDF drawing, or a worn bushing we measure and re-model.

Bushing drawings look simple but they carry bore fits, wall thicknesses and part numbers that identify a whole assembly. Before any file is opened we sign a mutual NDA — ours in English or Chinese, or your own form — and return a countersigned copy before work starts. Access is limited to the project engineer, the lathe programmer and the cell supervisor, with the file in a restricted folder rather than the open shop network. The cell is a camera-free area: no photographs, no video, no social posts, and no customer part kept on display or offered as a sample. Subcontracting requires your written approval, and at program close drawings and inspection data are deleted or returned with written confirmation.

Dongguan Changxinda Precision Technology Co., Ltd has machined custom metal parts since 2008 — 15+ years, 90 to 100 staff, 50–60% of output exported to North America and Europe, 200+ customers served, turnover in the RMB 10–20 million band. The plant runs CNC lathes, turn-mill combined centres with sub-spindle and live tooling, and 4-axis / 5-axis machining centres under an ISO 9001:2015 quality system, serving medical, robotics, automotive, aerospace, automation, laser, LED, lithium battery and precision instrument programs. Turning, boring, grooving, passivation coordination and inspection happen in our own plant in Dongguan.

Precision turned components from this plant ship into ten sectors. The list is what customers actually order, not a marketing wish-list.

All ten sectors run through the same plant and the same ISO 9001:2015 inspection discipline — only the material, finish and documentation package change.

• Prototype: 3–7 working days after drawing approval including passivation and gauging.
• Small batch 10–100 pcs: 7–14 working days.
• Repeat orders: released from archived program, collets and boring tool list — bore and steps come off the same tools, so the fit repeats.
• Capacity: 10,000 pieces per month across the plant.
• Visibility: a dated progress note with photos of your actual parts at turning, boring and inspection.
• Shipping: bores capped, parts oiled where required and bagged, foam-lined export carton, express or air and sea per your forwarder.
• Rush: weekly overtime slots held for line-down cases — give us the deadline and we confirm before the order.