Use a salvaged steel axle from a trailer or car rather than wood, but treat it as a beam with a stress budget: a steel pipe 30 mm across with a 3 mm wall, carrying 100 kg per wheel on a 150 mm arm, already sees about 94 MPa in bending and has little margin at 250 kg. Fit bushings or salvaged wheel bearings inside the wheel hub, because bare steel on wood or steel wears fast and the bearing set decides how long the axle lasts.
Part of Cart & Wagon Construction
A salvaged metal axle is a steel shaft, tube or complete axle assembly taken from a trailer or vehicle and repurposed under a hand-built cart, normally with its own or improvised bearings.
What To Salvage
The parent article names the sources:
- Trailer axles from boat trailers, utility trailers or camping trailers. These are the best: they are made for the job, and the stub axles and bearings often come with them.
- Rear axle shafts from cars, cutting the housing if necessary.
- Steel pipe of sufficient diameter, a minimum of 3 cm for light loads.
A complete trailer axle with its hubs and bearings is the easiest, because the bearings are already matched to the shafts. A bare car axle shaft usually ends in a flange or splines, so plan how the hub will be mounted before cutting anything.
How Much Load Can A Pipe Carry?
Treat the axle as a cantilever: the bending moment is the load per wheel times the arm from the support to the middle of the hub. Stress is M / Z, with Z = π (D⁴ - d⁴) / (32 D) for a tube of outside diameter D and inside diameter d.
A 30 mm tube with a 3 mm wall (assumed dimensions, so d = 24 mm):
- Z = π × (30⁴ - 24⁴) / (32 × 30) = π × (810,000 - 331,776) / 960 = about 1,565 mm³
| Load per wheel | Moment on a 150 mm arm | Stress |
|---|---|---|
| 100 kg (981 N) | 981 × 150 = 147,150 N·mm | 147,150 / 1,565 = 94 MPa |
| 250 kg (2,453 N) | 2,453 × 150 = 367,950 N·mm | 367,950 / 1,565 = 235 MPa |
Mild steel yields at roughly 250 MPa (a recalled handbook value, and the grade of a scrap pipe is unknown). So at 100 kg per wheel there is a static margin of about 2.7, which a rough road can halve, and at 250 kg per wheel the pipe is within about 6% of yielding and should not be used. That is why the carrier restricts 3 cm pipe to light loads.
A 50 mm tube with a 5 mm wall (d = 40 mm): Z = π × (50⁴ - 40⁴) / (32 × 50) = π × 3,690,000 / 1,600 = about 7,245 mm³, so 250 kg per wheel gives 367,950 / 7,245 = 51 MPa, about a fifth of the stress.
What You Need
- The salvaged axle, inspected clean of rust and cracks
- A hacksaw or torch to cut it to width, and files or a grinder for the ends
- Bushings or salvaged wheel bearings matched to the axle diameter (Axle and Bearing Design, Axle Box & Bearings)
- Grease (Axle Grease)
- Brackets, U-bolts or straps to hold it to the frame, and a linchpin per wheel (Axle Pin & Retention)
Method: Select, Check, Fit
Step 1: Inspect before cutting. Clean the axle and look for hairline cracks, especially near shoulders, welds and the flange root. A visibly bent or twisted axle means scrap. A cracked axle breaks without warning under a loaded cart.
Step 2: Size to the cart. Compare the load per wheel and the arm length against the stress table. Prefer the larger pipe whenever the choice exists.
Step 3: Cut to width. Cut to the bed width plus the two hubs and clearance, and square and chamfer the ends.
Step 4: Choose the bearing. If the axle has matching wheel bearings, fit the complete hubs. If it is bare pipe, fit bushings inside the hub: the parent article says bushings or bearings are needed, and salvaged wheel bearings from any vehicle work if you can match sizes.
Step 5: Fit and grease. Pack the bearings with grease, fit the wheel, set end play so the wheel turns freely without rocking, and fit the linchpin.
Step 6: Test at half load. Drive on the roughest surface the cart will meet and check for heat at the hubs and any movement at the brackets.
Common Mistakes
- Choosing a pipe by diameter only — the wall thickness and load per wheel decide the stress.
- Welding or heating a heat-treated car axle shaft — such shafts are commonly hardened, and heat or a weld can leave a brittle zone next to the repair (recalled metallurgy; avoid it).
- Mismatched bearings — a bearing a size too large on a shaft wobbles and wears quickly.
- No lubrication plan — sealed bearings are still finite; see Lubrication & Wear.
Safety
Cutting, lifting and a failed axle
Cutting an axle housing with a torch throws sparks and burns off coatings that give off fumes, so cut outdoors, with eye protection and well clear of dry material. A heavy axle lifted onto a frame can crush hands and feet, and an axle that fails under a loaded cart drops the bed and load: inspect for cracks, stay well within the stress budget and chock the wheels before working under or beside a cart.
What’s Next
- Learn next: Lubrication & Wear — grease for a salvaged bearing
- Combine with: Axle Types — fixed versus rotating axles