0.01mm Bore Concentricity Stepped Coupling Sleeve in 303 316L 17-4PH Stainless Steel with Single Clamping Boring

This is a stepped coupling sleeve: one bore takes a motor or gearbox shaft, the other bore takes a smaller driven shaft, and the step between them sets the axial position of the two. It exists because the two shafts are not the same diameter, and because the customer wants one rigid part between them instead of an adapter plus a coupling.

The critical number is not the size of either bore; it is how well the two bores share an axis. If the small bore runs 0.02 mm off the large one, the driven shaft is forced into an orbit on every revolution, and the bearing at the far end pays for it. We hold bore-to-bore concentricity at 0.01 mm by boring both diameters in the same clamping.

1. Drawing and fit review. We confirm both bore diameters and fits, step position, shoulder width, wall thickness and the drive method, then quote within one working day.
2. Material verification. 303, 316L or 17-4PH bar is checked against the mill certificate. 303 for general use, 316L for wet or washdown environments, 17-4PH where the sleeve is heat treated for strength.
3. Facing and rough boring. The blank is faced and both bores are roughed from one end with 0.3 mm of stock, so the finishing cuts remove an even amount from each diameter.
4. Stress relief where needed. Thin-wall sleeves are stress relieved between roughing and finishing, because boring removes material unevenly and the sleeve will otherwise close slightly after the last pass.
5. Finish boring both diameters. Both bores are finished in the same clamping from the same datum, which is what holds 0.01 mm bore-to-bore concentricity instead of the 0.03 mm typical of turning one end, flipping and turning the other.
6. Shoulder and outer diameter. The internal shoulder face is faced square to the bore axis within 0.01 mm, and the outer diameter is turned to 0.015 mm runout so the sleeve can be held in a bearing block if required.
7. Chamfers and deburr. Bore entries are chamfered to guide the shaft in without shaving a burr, and the internal step corner is relieved so the shaft shoulder seats on the face, not on a radius.
8. Passivation and inspection. Passivation, then bore gauge and air gauge checks on both diameters, CMM for concentricity and shoulder squareness, and a first article report with the batch.

The usual way to make a stepped sleeve is to bore one end, part off, flip the part and bore the other end in a second operation. It is faster, and it is the reason so many sleeves arrive with the two bores 0.03 mm apart. The second operation locates on a freshly turned outside diameter, so chuck runout becomes bore offset, and the error is invisible until the customer assembles the unit and hears it.

We bore both diameters in one clamping from one end, which limits us to sleeves where the boring bar can reach the far bore. Where the length-to-diameter ratio will not allow it, we use a line-bored second operation on a four-jaw with an indicating step, and we say so on the quotation rather than after the parts are made. The inspection report shows both bores measured against the same datum, so the number can be verified rather than trusted.

Bore sizes and fits, step position, shoulder width, outer diameter, keyway, cross hole, material grade and heat treatment are all built to your drawing. One piece is a normal order with no tooling charge and no setup fee, and the prototype follows the same inspection plan as a batch. If the wall between the two bores is thinner than 2 mm, our engineer flags the risk before cutting.

• NDA before files. Mutual non-disclosure is signed before drawings or samples are released, covering geometry, volume, end use and customer identity.
• No public reference. Confidential sleeves never appear as samples, catalogue items, website photos or trade fair parts.
• Separated cell. Sensitive work runs with named operators and project-coded programmes.
• Partner control. Heat treatment and passivation suppliers receive process specifications only.

Dongguan Changxinda Precision Technology Co., Ltd has machined custom parts since 2008. The plant runs turn-mill centres, CNC lathes with live tooling, four-axis and five-axis machining centres, employs 90 to 102 people under ISO 9001:2015, serves more than 200 customers, exports 50 to 60 percent of output and records annual sales of USD 10 to 20 million.

• Dates in writing. Prototypes 3 to 6 working days, batch orders 10 to 18 working days after drawing approval.
• Repeat orders skip setup. Programmes, boring bars and gauge sets stay on file.
• Bar stock on hand. Common stainless diameters are stocked.
• Early notice. If material, heat treatment or passivation threatens the date, you are told before the date is missed.
• Dispatch evidence. Photos, inspection report and packing list before shipment.

• ✓Consumer Electronics: phone, tablet and laptop housings, heat sinks, camera brackets, VR/AR headset structural parts, smart wearable shells
• ✓Automation & Industrial Equipment: automation fixtures, jigs, module frames, transmission sliders, motor mounts, sensor housings, conveyor line parts
• ✓Semiconductor & Vacuum Equipment: vacuum chambers, vacuum fittings, precision equipment bases, thermal isolation and insulation parts, inspection fixtures
• ✓Medical Devices: surgical instrument bases, diagnostic instrument housings, endoscope components, aesthetic device structural parts (medical-grade aluminum and stainless steel)
• ✓Automotive: new energy motor housings, battery end plates, sensor brackets, lamp structural parts, tuning parts, hydraulic valve blocks
• ✓Aerospace & UAV: aircraft structural parts, drone frames, landing gear parts, avionics instrument housings (lightweight precision parts)
• ✓Optics & Photonics: optical lens barrels, lens mounts, light source heat sinks, camera module brackets, inspection optical benches
• ✓Communications: 5G heat dissipation cavities, filter parts, signal adapter structural parts, telecom equipment housings
• ✓Robotics: robot arm joint parts, robot bases, reducer housings, AGV structural parts
• ✓Instrumentation: test equipment housings, precision gauge bases, flow meter parts, laboratory equipment accessories

Each sleeve is bagged with desiccant, seated in a foam tray so bore entries cannot be bruised, and packed in a five-layer export carton marked with part number, quantity and batch code. Sea freight ships on fumigation-free plywood pallets; neutral cartons are available.