CNC Turned Aluminum Stepped Threaded Shaft
Stepped threaded shafts turned from 6061-T6, with a bearing seat held to h7 and round within 0.01 mm, an M6 to M20 rolled thread concentric to the seat within 0.02 mm, shoulders square to 0.02 mm and a runout of 0.02 mm checked between centres before anodizing.
- Bearing Seat h7, 0.01 mm Round
- Rolled Thread, 6g
- Shoulder Square to 0.02 mm
- Runout 0.02 mm
*Send the bearing number and the torque through the thread. An aluminium shaft with a rolled thread will take about 60 percent of the torque of a steel one at the same size, and the thread is where it fails.
Aluminium Stepped Threaded Shaft Overview
An aluminium shaft is chosen to save weight on a moving axis. It still has to hold a bearing seat at h7 and a thread that does not strip, and both depend on the material staying straight after turning.
The shaft is turned between centres in two operations, the thread is rolled rather than cut, the seat is finished with a sharp positive tool at low feed, and the part is checked for runout before anodizing.
6061-T6 Aluminium
6061-T6 gives a stable seat after turning and takes a clear or black anodize that resists handling wear. At 60 mm diameter it weighs about a third of the steel shaft it replaces.
7075-T6 or 2024
7075-T6 is used where the shaft is highly loaded in bending, and 2024 where the thread has to take more torque, at the cost of corrosion resistance and a mandatory coating.
A 2 mm wall at an internal bore is the minimum for anodizing; thinner than that the coating pulls the bore oval and the shaft will not slide on its mating spigot.
Aluminium Shaft Specifications
Turning and threading data for aluminium shafts, with the seat and runout values that keep a bearing quiet.
| Specification | Machining Data | Specification | Machining Data |
|---|---|---|---|
| Product | Stepped Threaded Shaft | Machining Process | CNC Turning, Thread Rolling, Boring |
| Material | 6061-T6 Aluminium, 7075 on Request | Envelope | Ø 10 – 60 mm, 60 – 400 mm Long |
| Bearing Seat | h7, Roundness 0.01 mm | Seat Finish | Ra 0.8 µm Turned |
| Thread | M6 – M20, 6g, Rolled | Concentricity | 0.02 mm Thread to Seat |
| Shoulders | Square to the Axis Within 0.02 mm | Runout | 0.02 mm Between Centres |
| Steps | Diameter ±0.02 mm, Length ±0.10 mm | Wall at the Bore | 2 mm Minimum |
| Weight | 60 – 900 g | Coating Build | 15 – 20 µm Anodizing |
| Customization | Step Layout, Thread Length, Cross Hole, Flat, Colour | Lead Time | 5 – 7 Days Sample, 12 – 16 Days Batch |
| Inspection | Micrometer at Three Planes, Runout on Centres, Thread Ring Gauge | Packing | Thread Cap, Foam Sleeve, Tube |
Key Features of Our Aluminium Shafts
Turned on centres, thread rolled, seat masked before coating.
Seat Turned With a Positive Tool
Aluminium smears with a neutral tool, so the seat is finished with a sharp positive rake insert at 0.05 mm/rev, which gives Ra 0.8 µm and a round seat without a built-up edge.
Thread Rolled for Strength
A rolled thread in 6061 is about 30 percent stronger than a cut one and leaves no burr at the start, which matters because the thread is the weakest feature on an aluminium shaft.
Runout Checked Before Coating
The shaft is indicated between centres before anodizing; a shaft that runs out 0.05 mm cannot be corrected by coating, and the seat is re-cut if it does.
Seat and Thread Masked
Both features are masked during anodizing, so the bearing fit stays h7 and the thread stays 6g rather than being closed by 20 µm of oxide.
Light shaft that still holds a bearing?
Finishes for Aluminium Shafts
The seat and thread stay bare, the body carries the colour.
| Finish | Main Purpose | Finish | Main Purpose |
|---|---|---|---|
| Clear Anodizing | Corrosion protection, machined look | Black Anodizing | Drive and spindle shafts |
| Hard Anodizing | Wear surface where a seal runs | Bead Blasting | Even matte on the body |
| Masked Seat | Bearing fit stays h7 | Masked Thread | Thread stays 6g |
| Teflon Impregnation | Low friction on a sliding fit | Laser Marking | Length and batch code |
| Thread Cap | Protects the thread in transit | Seat Wrap | Protects Ra 0.8 µm |
| Salt Spray | 500 h on 6061 | Seat Recheck | h7 After Anodizing |
*Anodizing builds 15 to 20 µm and is brittle in bending; a shaft that flexes in service is better left clear anodized with a thin build than hard anodized.
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Turning an Aluminium Shaft
The bearing seat and the thread are turned on the same centres, so an anodized shaft still runs true after the coating has been cut back at the seat.
01. Bearing and Thread Review
Confirm the bearing fit, the thread size and the torque, then decide the step layout and where the part is held for the second operation.
02. Turn the First Side
Hold on the bar, turn the main diameter and the seat, face the shoulder square and leave 0.1 mm on the seat for the finish pass.
03. Turn the Second Side
Turn the part around in soft jaws on the finished diameter, indicated to 0.01 mm, then finish the remaining steps and the thread diameter.
04. Roll the Thread
Roll the thread with a die head, check with a ring gauge, and break the thread entry with a 1 × 45° chamfer.
05. Check, Mask, Anodize
Indicate runout between centres, mask the seat and thread, anodize, then re-check the seat size with a micrometer.
Send the bearing number and the step drawing, and we will quote a shaft turned on centres with the seat and thread masked before anodizing.
Aluminium Shaft FAQs
About 30 Nm with a rolled thread and 20 Nm if it is cut. Beyond that the thread pulls out before the shaft yields, which is why we always ask for the torque figure.
It would, by 20 µm, so the seat is masked. An unmasked seat turns an h7 shaft into an interference fit that cracks the coating when the bearing is pressed on.
Up to 400 mm between centres, with a steady rest. Longer than that the shaft deflects under the tool and the seat goes 0.02 mm oversize in the middle.
For light loads and moderate speed, yes. Above about 5 Nm continuous or 4000 rpm the shaft is usually steel, because aluminium fatigues at the thread root.
Ra 0.8 µm turned, or Ra 0.4 µm if the seat is roller burnished, which also raises the surface hardness by about 10 percent.
Yes, cut after turning with a 4 mm end mill. A keyway in 6061 should have radiused corners, since a square corner concentrates stress and cracks first.
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