Custom Turned 42CrMo4 Alloy Steel Spline Sleeve Coupling HRC 55 Carburized 60mm Outer Diameter

This spline sleeve coupling is machined from Alloy Steel 42CrMo4 (42CrMo4 (AISI 4140)) to ±0.015mm in the critical dimensions, then finished by Carburized HRC 55-60 ground flanks. It is produced on CNC turning centres that are dedicated to small and medium volume precision work, so every dimension on the drawing is generated by the machine rather than by hand fitting. Typical users are engineers who have already been let down by a supplier that quoted a tolerance it could not hold, and who need the part to fit the first time without sorting or rework on the assembly line.

• Carburized Tooth Flank: 0.8 to 1.2mm case at HRC 55-60 carries high contact stress without tooth spalling
• Ground Spline Flanks: Flanks are ground after heat treat to hold 0.02mm runout and quiet power transmission
• Tough Core Under Hard Case: Core stays at HRC 30-35 so the sleeve absorbs shock load without brittle fracture
• Distortion Controlled: Fixtured quench and a post heat treat sizing pass keep bore and spline concentric
• Magnetic Particle Tested: Each lot is MPI inspected for heat treat cracks before shipping

The process route is fixed before metal is cut. Bar stock is verified against the purchase specification and the heat number is logged, then a first article is turned and measured in full. Only after the first article is signed off does the lot run. Critical features on this spline sleeve coupling are controlled to ±0.015mm with a process capability target of Cpk 1.33 or better, and the operator checks the feature at a defined frequency with the gauge stated on the control plan. Where the drawing calls for Carburized HRC 55-60 ground flanks, the finishing step is carried out in house and the result is measured, not assumed. Sample parts go to the CMM for full dimensional verification, and the recorded results ship with the lot as a first article inspection report in PPAP level 3 format when a customer program requires it.

Questions are handled by engineers rather than by sales staff. Our team reviews each drawing for manufacturability, flags features that would drive cost without adding function, and proposes the tolerance band that actually matters for the assembly. That review is free and is returned within 24 hours together with a quotation. When a part fails in the field, we ask for the sample back, section it if needed and report what the failure mechanism was, because a supplier that cannot explain a failure cannot prevent the next one.

• Machines: 50+ CNC units including Swiss type lathes, 3, 4 and 5 axis machining centres and turn-mill centres from Citizen, Star, Doosan and Mazak.
• Quality lab: CMM, 2D vision measurement, roughness tester, hardness tester, salt spray chamber and spectral analyser for material verification.
• Team: 15+ mechanical engineers covering DFM review, process design, fixture design and failure analysis.
• Capacity: 500,000+ precision turned parts per month with stable output and on time delivery tracking.
• Quality system: ISO 9001:2015 certified, SGS audited, material traceability from mill heat to finished part.
• Export experience: parts shipped to 30+ countries across North America, Europe, Japan, Korea and Southeast Asia.

Gearbox input couplings, industrial pump drives, winch transmissions, agricultural PTO drive lines and machine tool spindle drives.

Parts are degreased, dried and packed so that the surface finish specified above arrives intact. Standard packing is VCI paper or individual PE bag, a partitioned foam tray for form features, and an export grade corrugated carton on a pallet, with the lot number and heat number marked on the outside. Parts are warranted against material and workmanship defects for 12 months from delivery. If a part is found outside the drawing, we replace it at our cost and we pay the return freight for the defective lot. Third party inspection by SGS, BV or TUV can be arranged before shipment at your request, and we work under NDA where drawings are confidential.

Q: Why carburize rather than through harden? A: A carburized case gives a hard wear surface over a ductile core. Through hardened 42CrMo4 at HRC 55 across the section is brittle and chips at tooth edges under shock load.

Q: Can you match the spline to an existing mating hub? A: Yes. Send a spline data sheet or a sample. We inspect it on a profile projector, confirm the fit class and cut a matched pair for trial assembly before production.

Q: How do you control distortion after heat treatment? A: Parts are racked on dedicated fixtures, quenched in controlled atmosphere and then sized. Bore and spline are checked after heat treat, not before.

Q: Do you provide heat treat certification? A: Yes. Each lot ships with case depth, surface hardness and core hardness readings plus the MPI report.

Q: How do you confirm the Alloy Steel 42CrMo4 material before it is machined? A: Every bar is checked against its mill certificate with an optical emission spectrometer before it goes to a machine. If the chemistry does not match the grade, the bar is rejected and returned. The certificate for your lot is filed under the heat number and can be sent with the shipment or on request.

Q: What happens if a delivered part measures outside the ±0.015mm tolerance? A: Send the measurement and the lot number. We check the recorded values for that lot, replace the parts at our cost and cover the return freight. Because each critical feature is recorded during production, we can trace the deviation to a tool wear step, a fixture shift or a gauge issue and correct the process before the next lot runs.

Send a 2D drawing, a STEP file or a sample and you will have a manufacturability review and a firm quotation within 24 hours. Trial orders from a single piece are accepted, so the tolerance claim can be checked on your own assembly before a production order is placed.