Aviation CNC Screw Machining
This page covers the threaded parts that hold aircraft systems together: bushings, studs, bolts, inserts, and small turned fittings. It is written for design and manufacturing engineers who need to judge whether a shop can hold aviation tolerances, and for buyers who compare quotes on more than price.
What matters before you send an RFQ
Which alloys work for aviation CNC screw machining
Most aviation threaded parts we run are small-diameter turned components: bushings, studs, spacers, and custom fasteners under Ø30 mm. The alloy choice usually comes from the drawing, but the shop still has to decide speeds, feeds, and tool path. That decision changes the thread flank quality more than most engineers expect.
Aluminium 7075-T6 is the common choice for structural fasteners and fittings. It machines fast, holds ±0.005 mm without much fuss, and takes anodize well. 6061-T6 is easier to weld and cheaper, but it is softer, so thread roots are more prone to smearing if the tool is dull. 2024 machines well too, though it needs a coating soon after cutting because it corrodes quickly.
Stainless 17-4PH (SUS630) is the workhorse for corrosion-resistant studs and bolts. In the H900 or H1025 condition it cuts like a medium steel; in the annealed condition it galls badly, especially on fine threads. 303 and 316L are easier to turn but weaker. 316L is often picked for brackets and fittings where corrosion resistance matters more than strength.
Titanium Ti-6Al-4V and Inconel 718 are where cost climbs. Both generate heat at the cutting edge, so we run lower surface speeds, heavier coolant flow, and fresh carbide. Thread milling is often safer than single-point threading on Ti-6Al-4V because it reduces radial pressure on the thin wall.
- 1Aluminium6061, 6061-T6, 2024, 5052, 5083, 6063, 6082, 7075, ADC12
- 2Stainless303, 304, 316, 316L, 420, 430, 431, 440C, 17-4PH (SUS630)
- 3Steel1018, 1045, 4130, 4140, 4340, A36, tool steel
- 4Titanium and specialTA1, TA2, TC4 (Ti-6Al-4V), Inconel, magnesium AZ31B / AZ91D
Threads, tolerances, and what the machine can hold
Thread class decides how the part fits, and it decides how we gauge it. A 3A/3B thread has a tighter pitch diameter than 2A/2B, so it needs a ring or plug gauge set to the right class. If the drawing only says "M6 thread," we will ask before cutting. Guessing here wastes a whole batch.
On a mill-turn center we can cut the thread and the body in one setup, which keeps the thread concentric to the shank. That matters on long studs where a second op can add 0.02 mm of runout. For parts with a thread under Ø6 mm, we often thread mill instead of using a die head. Thread milling gives a cleaner root and lets us adjust the pitch diameter by a few microns if the gauge runs tight.
Tolerance is not a single number for the whole part. A Ø8 mm shank and a 40 mm length need different attention. We hold ±0.005 mm (±0.0002 in) on critical diameters, and the 5-axis centers handle position tolerances on hole patterns without a second fixturing step.
Surface finish matters on threads that will be torqued repeatedly. Ra 0.8–1.6 μm is normal for a turned thread flank; Ra 0.2–0.8 μm is for sealing faces and bearing journals. As-machined at Ra 1.6–3.2 μm is fine for non-critical spacers. Say which surfaces need the tighter finish so we do not polish the whole part.
Why the setup decides the batch
Small threaded parts are hard to hold. A Ø5 mm stud with a 30 mm shank will deflect if the chuck pressure is too high, and it will slip if the pressure is too low. We use collets sized to the actual bar stock, and for thin-wall bushings we sometimes turn a soft jaw or a sacrificial stub so the part stays round.
Bar feeders help on runs above a few hundred pieces. They keep the stock concentric and reduce the number of times an operator touches the part. For one-off prototypes we cut from bar and support the free end with a tailstock or a steady rest. That is slower, but it holds the same tolerance.
The number of setups drives both cost and error. A part that needs three ops has three chances for stack-up. On our 16 mill-turn centers, we combine turning, milling, and threading so a threaded fitting comes off the machine complete. Fewer setups also mean faster turnaround: production can start within 24 hours of a released program.
Fixtures must not mark the part. Aluminium and titanium scratch easily. We use nylon or brass contact points where the finished surface will be visible, and we plan the order of operations so any clamping mark is removed by a later pass.
Finishes that change the thread
Coating a threaded part is not a cosmetic step. Anodize, electroless nickel, and plating all add a layer. Hardcoat anodize can add 25–50 μm per surface, which is enough to make a nut bind. When a thread will be coated, we cut it undersize on purpose and let the coating bring it back to class. This has to be agreed before machining.
For aluminium parts, clear or colour anodize is common on fittings and brackets. Hardcoat anodize gives a wear surface on bushings. Conductive anodize is used where the part needs both corrosion protection and electrical continuity. Electroless nickel is often chosen for steel and stainless because it covers evenly, including inside threads.
Bead blasting and tumbling remove tool marks and edge burrs. We tumble most small threaded parts before final inspection because a burr on a thread crest can cause a false gauge reading. Brushing and polishing are reserved for visible surfaces or sealing faces.
Laser marking is used for part numbers and lot codes. Minimum character height is 1.5 mm, so tiny screws may need a different marking method. Marking is done after finishing whenever possible, because blasting can erase a shallow mark.
Matching part type to process and finish
Use this table to pick the process route before quoting.
| Part type | Typical alloy | Process route | Finish |
|---|---|---|---|
| Structural bolt, Ø6–20 mm | 7075-T6, 4340 | Mill-turn, thread mill | Anodize or black oxide |
| Corrosion-resistant stud | 17-4PH, 316L | Turn, single-point thread | Electroless nickel |
| Thin-wall bushing | 6061-T6, 316L | 5-axis, soft jaw | Hardcoat anodize |
| High-temp fitting | Inconel 718, Ti-6Al-4V | Turn, thread mill, slow passes | Passivate, no coating |
| Precision spacer | 2024, 303 | Bar feed, one setup | As-machined or tumble |
| Sealing plug | 316L, brass C36000 | Turn, lap seal face | Ra 0.2–0.8 μm polish |
When to choose which route
If the thread is the critical feature, pick a shop that gauges to class and can thread mill. If the body geometry is complex, pick a mill-turn route so the thread stays concentric. If the part will be coated, decide the coating before the thread is cut.
Common questions
What tolerance can you hold on a small threaded part?
We hold ±0.005 mm (±0.0002 in) on critical diameters and Ra 0.2–0.8 μm on sealing faces. The limit is usually the wall thickness, not the machine. A Ø4 mm stud with a long unsupported shank will deflect, so we add a tailstock or steady rest.
For thread class, we gauge with ring or plug gauges matched to the class on the drawing. If the drawing does not state a class, we will ask before cutting.
Do you cut Inconel and titanium threads?
Yes. Inconel 718 and Ti-6Al-4V are regular materials for us. Both need lower surface speeds, high coolant pressure, and fresh carbide. On titanium we often thread mill instead of single-point threading to reduce radial load on thin walls.
Expect longer cycle times than aluminium or stainless. Send the drawing and we will confirm the route in the DFM review.
How does coating affect the thread fit?
Anodize and plating add thickness. Hardcoat anodize can add 25–50 μm per surface, which will make a nut bind if the thread was cut to nominal size. We cut the thread undersize and let the coating bring it to class.
Tell us the coating and the target class at quoting. Changing the coating after the parts are cut usually means scrapping the batch.
What is the minimum order quantity?
There is no minimum order quantity. We run from one prototype to 10,000+ part runs. Prototypes are usually cut from bar with a tailstock; production runs use bar feeders and mill-turn centers.
A quotation and free DFM analysis come back within 12 hours. Production can start within 24 hours of a released program, and parts ship in 3–5 days.
How do you handle inspection and documentation?
We inspect 100% of parts before shipment: raw material check, in-process monitoring, and final inspection. Reports are available on request.
Our quality system is certified to ISO 9001:2015, IATF 16949:2016, ISO 13485:2016, and ISO 27001:2022. Uploads are secure and confidential; an NDA is available on request.
Can you mark parts with a lot code?
Yes. Laser marking and engraving are available, with a minimum character height of 1.5 mm. Very small screws may need a different marking method because the mark would be too shallow to read.
Marking is done after finishing where possible, since bead blasting can erase a shallow mark.
Send the drawing, get a process route
Upload your threaded part and we will review material, thread class, and finish before quoting. A quotation and free DFM analysis come back within 12 hours.
12-hour quote100% inspectionNo MOQNDA on request
More from the shop floor
We publish setup notes, tooling trials and inspection data from the factory floor.
