Wexmar offers 4340 steel CNC machining for parts that need high strength and toughness in heavy cross sections. 4340 adds nickel to the chromium molybdenum chemistry of 4140, so it hardens more deeply and resists impact and fatigue better at the same hardness. We machine 4340 shafts, pins, gears and structural fittings on lathes and horizontal mills in Canastota, New York, for industrial, aerospace hardware and defense build-to-print customers.
How 4340 machines
In the annealed condition, 4340 has an approximate machinability rating of 57 against AISI 1212 at 100. Prehardened 4340 falls to about 45. The nickel content makes the material tougher to shear than 4140, so cutting forces are higher, edges wear faster, and chips come off hotter. It rewards rigid setups, conservative speeds and fresh edges more than aggressive feeds.
Tolerances and surface finish on 4340
Typical tolerances are plus or minus 0.001 in on turned diameters, with tighter bearing fits held when the process is proven on first article. Milled features on our horizontal machining centers typically hold plus or minus 0.001 to 0.002 in. Surface finish of 63 Ra is typical for milled faces and 32 Ra for turned diameters, and prehard stock often turns a cleaner finish than annealed. Centerless and surface grinding are available in-house for ground fits. Treat these numbers as typical, not guaranteed.
Shop-floor gotchas with 4340
- Heat at the edge. 4340 holds heat in the chip and at the insert. Flood or high pressure coolant, coated carbide and moderate surface speeds keep crater wear under control.
- Deep hole drilling. The alloy grabs drills in deep holes. Peck cycles, through-coolant carbide drills and careful chip evacuation prevent broken tools in bores more than a few diameters deep.
- Sequence around heat treat. Parts heat treated to high strength levels after machining will move and scale. We rough, send out for hardening, and then finish turn or grind the critical features.
- Hydrogen embrittlement. At high hardness, 4340 is sensitive to hydrogen from plating and acid cleaning. Any plated part gets a relief bake specified with the processor.
- Surface integrity. Grinding burns and abusive machining can reduce fatigue life, so finishing passes are kept light and cool.
Heat treat and finishing options
We arrange quench and temper to a drawing hardness, normalizing, stress relieving and nitriding through qualified outside processors. Common finishes include black oxide, cadmium replacement zinc nickel plating, manganese phosphate, electroless nickel and hard chrome. Shot peening and magnetic particle inspection are also sourced outside when a print requires them, and we manage the routing so the part returns to our floor for final inspection.
Typical 4340 parts and which machines run them
- Heavy duty shafts, axles and splined drive members, turned on our larger Mazak lathes
- Clevis pins, hinge pins and quick release pins, run on Swiss-type machines up to 32 mm
- Gear blanks and pinion shafts machined before and after hardening
- Structural fittings, lugs and brackets milled on 4-axis horizontal machining centers
- Bolts, studs and threaded adapters for high load joints
Long shafts with cross holes and flats run complete on our CNC turning equipment with live tooling, which keeps concentricity and reduces handling between operations.
4340 cost index vs related materials
| Material | Approx. machinability (1212 = 100) | Cost index vs 6061 | Notes |
|---|---|---|---|
| 6061-T6 aluminum | ~180 | 1.0 | Reference material |
| 1045 cold drawn | ~57 | 1.3 | Plain carbon, lower strength |
| 4140 annealed / prehard | ~66 / ~50 | 1.6 | Common alloy steel |
| 4340 annealed / prehard | ~57 / ~45 | 2.0 | Deep hardening, high toughness |
| S7 / H13 annealed | ~45 | 2.6 | Tool steels for impact and heat |
| 17-4 PH stainless | ~40 | 2.8 | High strength with corrosion resistance |
Values are typical and illustrative for a comparable part; actual quotes depend on geometry, quantity, tolerances and mill pricing.
Applications for 4340 alloy steel machining services
4340 is specified for aerospace hardware, ground vehicle and weapons components, heavy equipment drivetrains, oil field tools, and high load industrial pins and shafts. Our government work runs under a CAGE code with WAWF/PIEE invoicing and DFARS 252.225-7009 compliant specialty metals sourcing when required; details are on our government and defense machining page. For moderate strength parts where 4340 may be more than the design needs, the 4140 steel machining page covers the lower cost alternative. Customers looking for a precision 4340 machine shop in Central New York can expect material certs, heat-lot traceability and AS9102 format first articles on request.
Getting a quote
To price 4340 work, upload a drawing for an instant estimate or call (315) 400-2654. A human estimator confirms every quote, including heat treat, finish and inspection requirements.