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Micro Machining±0.01 mm Roundness
SUS304Impact-Rated Body
CNC Machining Case Study · Precision Components
Micro-Machined Stainless Steel Shaft-Sleeve Assembly — ±0.01 mm Roundness for Drop-Impact Durability
A portable diagnostic equipment maker needed a micro shaft-sleeve assembly that survived repeated drop impacts without binding or wearing loose. Rejin CNC machined SUS304 stainless steel sleeves to ±0.01 mm roundness — surface-hardened, full-dimension inspected, and small-batch flexible for fast design iteration.
See How We Solved ItGet a Free DFM Review
SUS304Stainless steel, impact & wear rated
±0.01 mmRoundness held, CMM verified
100%Full-dimension inspection
IATF 16949Certified production & QC
The Story
How This Project Really Began
A real engineering story — a component measured in microns, and the supplier who finally held the tolerance.
Some components are so small you never see them — until they fail. The shaft-sleeve assembly in this project sits inside a portable device, where a few microns of wear or a hairline distortion turns smooth operation into wobble, binding and early failure.
The customer was developing a new generation of portable diagnostic equipment — compact, battery-powered, built for field use, and designed to be carried and dropped far more often than it should be. The shaft-sleeve assembly had to carry a rotating load through thousands of cycles, resist shock from repeated drops, and hold its fit for the life of the device. On a component barely wider than a pencil lead, that is a demanding specification.
The first supplier’s samples looked acceptable under a loupe. In testing, they failed: roundness drifted beyond spec, the sleeve bound against the shaft after a few dozen cycles, and drop impacts left the assembly loose. A second shop quoted a cheaper material that galled under load. Neither understood what micro CNC machining demands at this scale.
The customer’s engineering team was then referred to Rejin CNC. Instead of quoting from the drawing alone, our engineers reviewed the assembly with a DFM-first eye: material selection, surface hardening for wear life, and a grinding strategy to hold roundness within ±0.01 mm — then proposed a small-batch production plan so the customer could iterate the design quickly before committing to volume.
“In micro components, roundness is strength. A few microns decide whether a shaft lasts one drop or ten thousand.”
How the first samples changed the program. The first batch arrived with roundness verified on every part — measured, not assumed. Drop-impact testing passed with margin, and assembly fit was consistent across all samples. The small-batch schedule let the customer validate three design iterations in six weeks instead of six months, and every iteration came back with the same precision. That first batch set the standard for everything that followed.
The Customer’s Pain Points
Why Previous Suppliers Could Not Deliver
Six problems that failed two candidate shops before Rejin CNC.
1
Micro tolerance drift
Sleeve roundness exceeded spec by microns, causing binding and uneven wear once assembled with the shaft.
2
Drop-impact failure
Parts deformed or galled under shock loads, killing device reliability in real-world use.
3
Surface wear
Soft untreated surfaces wore loose over cycles, shortening the assembly’s fit life and forcing early replacement.
4
Batch variation
Dimensions drifted between runs, breaking assembly consistency and wasting engineering time on re-tolerance.
5
No small-batch flexibility
Suppliers demanded large MOQs, making fast design iteration expensive and slow.
6
Limited engineering support
No DFM feedback on micro features, material choice or surface treatment — problems surfaced only after parts arrived.
Project Overview
Micro Stainless Steel Shaft-Sleeve Assembly for Portable Device Systems
A micro-machined shaft-sleeve assembly in SUS304 stainless steel, engineered for drop-impact resistance, micron-grade roundness and long-term fit life — produced with full in-house machining, surface hardening and 100% dimension inspection, from fast small-batch iteration to volume.
SUS304 stainless steel, impact-resistant and wear-rated body
Roundness controlled within ±0.01 mm, CMM verified
Controlled surface hardness for extended wear life
100% full-dimension inspection with data per lot
Small-batch supply for fast design validation and iteration
Our Engineering Solution
How We Engineered the Part for Repeatable Production
The difference was never a single machine — it was a complete micro-machining system built around one assembly.
Material
SUS304 Stainless Steel
Impact-resistant and wear-rated body — the right grade for shock loads, corrosion resistance and long fit life in compact mechanical systems.
Machining
Micro CNC Turning & Milling
Precision micro geometries machined on dedicated 5-axis and turning centers, with low-stress toolpaths that protect thin-wall features.
Roundness
Grinding to ±0.01 mm
Precision grinding after machining holds roundness within ±0.01 mm — verified on a CMM for every part, not sampled.
Surface
Controlled Surface Hardening
Surface hardness controlled to spec for wear resistance, extending fit life through thousands of operating cycles.
Inspection
100% Dimension Check
Roundness, diameters and lengths measured on every part with data archived per production lot.
Flexibility
Small-Batch Production
Flexible scheduling supports fast iteration and low-volume hardware testing before scaling to mass production.
Challenges We Overcame
Four Production Battles, and How We Won Each One
Real problems from the micro-machining floor — root cause, fix, and the result we hold today.
🧱
Micro Thin-Wall Distortion
ProblemThin-wall micro features warped under cutting forces — a few microns of distortion that failed roundness checks.
FixLow-stress toolpaths, dedicated micro fixtures and separated rough/finish passes protect the geometry during machining.
ResultRoundness held within ±0.01 mm on every part — verified on CMM, batch after batch.
🎯
Roundness Drift
ProblemEarlier parts drifted out of round during finishing, causing binding with the mating shaft.
FixPrecision grinding after CNC machining, with in-process measurement before final pass.
Result±0.01 mm roundness held consistently — assembly fit remained smooth across all batches.
🛡️
Surface Wear & Galling
ProblemUntreated surfaces galled under load, wearing loose after repeated cycles and shortening fit life.
FixControlled surface hardening applied uniformly, with hardness verified per batch.
ResultDrop-impact and wear testing passed with margin — no binding, no galling, no early failures.
🚚
Small-Batch Economics
ProblemThe customer needed fast design iteration, but standard suppliers imposed large MOQs and long cycles.
FixFlexible small-batch scheduling with dedicated changeover — three design iterations validated in six weeks.
ResultFast iteration and validation at low cost — then a clean scale-up path when the design was frozen.
Manufacturing Process
From Bar Stock to Micro Sleeve in 6 Controlled Steps
Every step is documented with in-process inspection, so quality is built in — not inspected in at the end.
1 Material Selection
SUS304 stainless steel bar stock selected for impact resistance, corrosion resistance and machinability at micro scale.
2 Micro CNC Machining
Precision turning and milling produce the micro geometry — bores, faces and bearing surfaces held with low-stress toolpaths.
3 Precision Grinding
Grinding brings roundness and surface finish to ±0.01 mm spec with in-process measurement.
4 Surface Hardening
Controlled surface treatment hardens the wear surface uniformly, extending fit life through thousands of cycles.
5 100% Dimension Inspection
Roundness, diameters and lengths CMM-measured on every part — data archived per lot for traceability.
6 Anti-Corrosion Packaging
Parts cleaned, rust-protected and individually packed to arrive ready for assembly.
Micro stainless steel sleeves — roundness and finish verified on every part.
Why micron-grade roundness matters
A few microns of out-of-roundness means a shaft that binds, wobbles, or wears loose over time. Holding ±0.01 mm on every part is what turns a component into a reliable system — and it is the standard we held from the first sample to full production.
Quality Assurance
Measured Results, Not Promises
Every key specification is verified on every production batch — data archived per lot for full traceability.
Specification
Requirement
Achieved
Method
Roundness
±0.01 mm
±0.01 mm
CMM measurement
Critical diameters
Per drawing
100% in spec
CMM measurement
Surface hardness
Per wear spec
Uniform
Hardness tester
Drop-impact resistance
Pass testing
Passed
Impact test
Salt spray resistance
48 h, no corrosion
Passed
ASTM B117
Batch consistency
100% dimension check
100% pass
Full-dimension CMM
Why Rejin CNC
What Makes Us Different From a Commodity Machine Shop
The customer compared us against shops that claimed micro capability. Here is what closed the deal.
vs. quote-as-is shops
DFM before the order
We review the drawing and flag micro-feature, material and surface issues before you spend on tooling — free and standard for every project.
vs. sampled inspection
100% dimension inspection
Roundness and critical dimensions are CMM-measured on every part — a defect never ships to your line.
vs. rigid MOQs
Small-batch flexibility
Fast iteration and low-volume hardware testing without large minimum order commitments — then a clean scale-up path.
vs. sales-led support
Engineers answer your questions
You talk directly to the people who run the machines and the process — technical answers in hours, not sales promises in weeks.
Project Results
What the Micro-Machining Program Delivered
The first batch fully met the customer’s drop-impact and fit-life standards, and iteration has only gotten faster since.
±0.01 mmRoundness held on every part
100%Drop-impact tested and passed
0Binding or galled joints in field use
4×Faster design iteration vs. previous supplier
Customer Feedback
What the OEM Engineers Say
Direct quotes from the people who run this program on the customer side.
“The roundness is verified on every part — we stopped worrying about fit the moment the first batch arrived.”
Mechanical LeadMedical Device OEM
“We validated three design iterations in six weeks. No other supplier gave us that kind of speed with the same precision.”
Product ManagerDiagnostic Equipment Brand
“Drop-impact testing passed with margin on the first try. The surface hardening made a real difference to our reliability numbers.”
Reliability EngineerMedical Device OEM
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