01
Distortion after quenching
A 4140 shaft held at ±0.01 mm comes back from hardening bowed by 0.08 mm. There is no stock left to straighten it. The part is scrap, and the heat-treat cycle plus freight is already paid for.
Alloy Steel CNC Machining
CNC Alloy Steel Machining for Load-Bearing Parts
We machine 4140, 4340, 4130, 1018 and tool steel into shafts, housings, gears and fixtures. 127 CNC machines, ±0.005 mm tolerance, and a DFM review back to you within 12 hours.
4140 / 4340 / 4130±0.005 mmØ400 mm rotary table4,000 mm max sizeRa 0.2–0.8 μm1 pc to 10,000+
15 yearsMachining alloy steel since 2011
127High-precision CNC machines
±0.005 mmAchievable tolerance
99.99%Qualification rate
Where these jobs go wrong
Four Problems That Show Up After Heat Treat
Parts rarely fail because the drawing was hard. They fail because something moved after the cut.
02
Tool wear turns into taper
4340 at 30 HRC eats carbide edges. On a long bore, a worn insert cuts a taper that only shows up on the CMM. By then the batch is finished and every piece carries the same drift.
03
Chatter on thin walls
A bearing housing with a 3 mm wall rings during boring. The shop slows the feed, the cycle time doubles, and the surface still reads Ra 3.2 μm where the seal needs to sit.
04
Hardness and finish conflict
The print calls for 40 HRC and Ra 0.4 μm on the same face. Cut it soft and it tears. Cut it hard and the tool deflects. Someone has to decide the sequence before the first chip.
How we run it
Cut It Right the First Time, Then Prove It
Two things decide whether an alloy steel part passes: the order of operations, and how the cut behaves on that specific heat lot.
Machining strategy
Rough, Stress Relieve, Then Finish
For any 4140 or 4340 part that will be hardened, we rough with 0.5–1.0 mm of stock left on critical faces, send it for stress relief, then finish after the final heat treat. That single change in sequence removes most of the movement people blame on the material.
When the hardness is above 35 HRC we switch to CBN or coated carbide and take lighter depths. Feeds come down, but the geometry stays where the print says it should.
- 1Pre-hardened stock4140 at 28–32 HRC machined without a post-heat operation
- 2Hard turningUp to 45 HRC on bearing journals and seal faces
- 3In-process probingBore and face positions checked before the part leaves the spindle
Geometry and access
Five Axes for Parts With No Good Datum
Alloy steel housings and manifolds often have features on four or five faces. Every re-fixture adds error, and on a 20 kg part the setup alone can cost more than the cutting. Our 16 simultaneous 5-axis centers reach those faces in one clamping.
The Ø400 mm rotary table and 4,000 mm travels cover everything from a 30 mm spool valve to a full-length machine bed. For long shafts, the 16 mill-turn centers cut and turn without a second setup.
- 1One setup, five facesPosition tolerance held across features that share a datum
- 2Mill-turnØ400 mm turning plus milling on the same program
- 3Deep boresGun drilling and long-reach boring on hydraulic blocks
Material selection
Which Alloy Steel Grade Fits the Job
Pick the grade by the load and the wear surface, not by what is in the rack.
| Grade | Typical use | Machinability |
|---|---|---|
| 1018 | Low-stress brackets, spacers, weldments | Easy, good finish |
| 1045 | Shafts, studs, lightly loaded gears | Moderate, gummy at low speed |
| 4130 | Airframe fittings, thin-wall tubes, weldments | Good, welds cleanly |
| 4140 | Hydraulic rods, mold bases, gears at 28–32 HRC | Good pre-hardened, harder after quench |
| 4340 | High-load shafts, landing gear, connecting rods | Tougher, needs rigid setups |
| A36 | Frames, base plates, non-critical structure | Very easy, poor wear resistance |
| Tool steel | Dies, punches, wear plates, cutting edges | Hard, slow speeds, light depths |
What we do
Services Around Alloy Steel Parts
One shop for the cut, the finish and the inspection report.
01
5-Axis CNC Machining
Sixteen simultaneous 5-axis centers for housings, manifolds and parts with features on five faces. One clamping, one datum.
02
4-Axis CNC Machining
Twelve four-axis mills for shaft work, cross-drilled parts and anything that needs indexed faces around a centerline.
03
CNC Milling & Turning
Twenty-seven three-axis machines and sixteen mill-turn centers cover flat plates, long beds, and turned parts up to Ø400 mm.
04
Rapid Prototyping
Single alloy steel pieces cut from bar or plate. Useful when you need to test a fit before committing to a batch.
05
Heat Treat & Finishing
Hardening, black oxide, electroless nickel, zinc plating, bead blasting and polishing arranged as one sequence.
06
Inspection & Reporting
Raw material check, in-process monitoring and final inspection. Dimensional reports on request with the shipment.
Capability range
What the Machines Can Hold
Numbers to check your part against before you send the file.
| Item | Range | Notes |
|---|---|---|
| Tolerance | ±0.005 mm | On critical bores, journals and bores |
| Surface finish | Ra 0.2–0.8 μm | Fine finish on seal and bearing faces |
| Max part size | 4,000 × 400 × 150 mm | Long beds, rails and base plates |
| Rotary capacity | Ø400 mm table | Indexed and simultaneous work |
| Order quantity | 1 pc to 10,000+ | No minimum order quantity |
| Quote turnaround | 12 hours | With free DFM analysis |
| Production start | Within 24 hours | After drawing release |
| Typical shipping | 3–5 days | For standard alloy steel parts |
Why GreatLight
Six Reasons Alloy Steel Buyers Stay
15Y
Fifteen years on steel
Working alloy steel since 2011. The feed and speed tables for 4140 at 30 HRC are already written down, not guessed at.
±0.005
Tolerance we can hold
0.005 mm on critical features, with in-process probing so a drift is caught on the machine, not at final inspection.
16
Simultaneous 5-axis centers
Complex housings cut in one setup. Fewer re-fixtures means fewer stacked errors on bolt patterns and bores.
12 h
Quote and DFM in 12 hours
You get a price and a manufacturability note. If a wall is too thin or a corner needs a tool change, we say so before cutting.
100%
Inspected before shipping
Every part, not a sample. Raw material check, in-process monitoring and final inspection with reports on request.
ISO
Audited processes
ISO 9001:2015, IATF 16949:2016, ISO 13485:2016 and ISO 27001:2022 cover quality, automotive, medical and data handling.
7,600 m²Manufacturing space
150Technicians on staff
3Wholly-owned plants
< 2%Historical late-delivery rate
Industry results
What Alloy Steel Parts Have to Do
Aerospace fittings
4130 fittings and brackets where weight and weld quality both matter.
- ±0.005 mm
- Ra 0.8–1.6 μm
- 100% inspection
Automotive & EV
4340 shafts and 4140 housings that run under load and vibration.
- IATF 16949
- 3–5 day shipping
- 1 pc to 10,000+
Industrial machinery
Tool steel wear plates, punches and dies held to fit at assembly.
- Hard turning to 45 HRC
- Ø400 mm rotary
- 4,000 mm travel
Hydraulics & energy
4140 rods and manifolds with deep cross-drilled passages and seals.
- Ra 0.2–0.8 μm
- Deep bore
- 12 h quote
FAQs
Questions Engineers Ask Before Ordering
Should I send 4140 pre-hardened or annealed?
If the finished part needs 28–32 HRC and the geometry is simple, pre-hardened stock saves a heat-treat cycle and the distortion that comes with it. We machine it directly and skip the post-quench operation.
When the print calls for 40 HRC or above, start annealed. We rough, you heat treat, we finish. That order keeps the critical dimensions in tolerance.
How much stock do you leave for heat treat?
For 4140 and 4340 going to 40 HRC or higher, we leave 0.5–1.0 mm on critical faces. Thinner stock risks a hard skin that the finish pass cannot clean up.
Long parts move more than short ones. On a shaft over 500 mm we bias the allowance toward the ends, where bowing shows up first.
Can you hold ±0.005 mm on a hardened part?
Yes, on features cut after heat treat. Hard turning with CBN or coated carbide holds that tolerance on bearing journals and seal faces up to about 45 HRC.
Features cut before hardening will not hold it. If the print puts a tight tolerance on a face that gets quenched, we flag it in the DFM review and propose a sequence change.
What surface finish can alloy steel take?
Ra 0.8–1.6 μm is standard for most turned and milled alloy steel. Sealing faces and bearing journals go to Ra 0.2–0.8 μm with a finishing pass and the right insert geometry.
Harder grades reach a better finish more easily than soft, gummy ones. 1018 at low hardness tends to tear, so we adjust the edge radius and feed instead of chasing the number with speed.
How do you handle thin-wall chatter?
We start by stiffening the setup rather than slowing the cut. Soft jaws, a tailstock or a temporary web across the bore usually removes the ringing.
If the wall is under about 2 mm and the part is long, we may recommend a stress-relief step between roughing and finishing. That is cheaper than fighting the vibration through the finish pass.
Do you machine tool steel as well as structural grades?
Yes. Tool steel, including D2 and similar grades, is cut with lighter depths and slower speeds. It is common for dies, punches and wear plates.
The limit is hardness. Above roughly 45 HRC we recommend grinding or EDM for the final dimensions rather than turning.
What is the minimum order quantity?
There is none. We run from one prototype piece to 10,000-plus part runs. A single alloy steel sample is a normal order for us.
If you are validating a design, send the drawing for one piece first. The DFM notes from that run usually carry over to the production batch.
How do you keep drawings confidential?
Uploads are handled as confidential and we work under ISO 27001:2022 for data handling. An NDA is available on request before you send anything.
If your program requires it, tell us at the quote stage and we will have the agreement in place before the files move.
Send Your Alloy Steel Drawing
Upload the file and get a price plus a manufacturability note within 12 hours. One piece or ten thousand, the review is the same.
12-hour quote100% inspectionNo minimum order quantityNDA on request
