Make a wooden axle from the hardest straight timber available, such as oak, ash, locust or hickory, at least 130 cm long and 10-12 cm thick, reduced to a smooth, slightly tapered journal of 5-6 cm for the last 15 cm at each end, with a linchpin hole near each tip. Softwood wears through in days, and a journal worn from 5.5 to 5.0 cm in diameter carries a third more bending stress, so size the journal for the worn state, not the new journal.
Part of Cart & Wagon Construction
A wooden axle is a fixed hardwood beam under a cart whose ends are shaped into journals that the wheel hubs turn on.
The Journal Is Where The Axle Fails
The axle carries the whole load into the wheels, and it is thinnest where the wheel sits. The parent article gives a body 10-12 cm thick, reduced to 5-6 cm over the last 15 cm at each end. That neck is a cantilever, and it is the section that breaks.
Worked check
Bending stress in a round section is M / Z, where Z = π d³ / 32. Assume a cart of 500 kg total, so 250 kg on each wheel, and a lever arm of 0.20 m from the bracket that supports the axle out to the middle of the hub (an assumed distance).
- Load per wheel = 250 kg × 9.81 = 2,453 N
- Bending moment M = 2,453 N × 0.20 m = 491 N·m
| Journal diameter | Z = π d³ / 32 | Stress = M / Z |
|---|---|---|
| 6.0 cm | 2.12 × 10⁻⁵ m³ | 23 MPa |
| 5.5 cm | 1.63 × 10⁻⁵ m³ | 30 MPa |
| 5.0 cm | 1.23 × 10⁻⁵ m³ | 40 MPa |
Going from 5.5 to 5.0 cm multiplies the stress by (5.5 / 5.0)³ = 1.33, a third more. Air-dry oak, ash and hickory break in bending at very roughly 90-140 MPa (recalled handbook values, not measured here). Against about 100 MPa, a 5.0 cm journal has a static margin of 100 / 40 = 2.5, and a rough road can double the load for an instant (an assumed factor of 2), which leaves 1.25. That is thin. Hence the advice to keep the journal at the top of the carrier’s 5-6 cm range and to replace or sleeve a journal that has worn down.
What You Need
- A straight billet of oak, ash, locust or hickory, free of knots in its central section, 130 cm or more long and 10-12 cm thick (Wood Seasoning)
- Axe, drawknife, spokeshave and a brace and auger (Woodworking)
- Sand or a smooth stone for finishing
- A fire for hardening the journals
- Grease (Lubrication & Wear)
The length is the bed width plus two wheel hubs plus clearance.
Method: Shape, Drill, Harden, Mount
Step 1: Select Choose a straight piece at least 130 cm long. Check along the grain for twist.
Step 2: Shape the arms Taper the ends slightly, keep them round and make them very smooth. Reduce the diameter to 5-6 cm for the last 15 cm on each side.
Step 3: Drill the pin holes Drill a hole near each tip for the linchpin (Axle Pin & Retention). Position it beyond the end of the hub, where the bending moment is nearly zero, so the hole removes strength where little is needed.
Step 4: Fire-harden the journals Char the surface lightly, then rub it smooth with stone or sand. The carrier says this greatly raises wear resistance. Because rubbing off the char reduces the diameter, leave the journal a little oversize to start: removing 1 mm of radius from a 5.5 cm journal gives 5.3 cm, and (5.3 / 5.5)³ = 0.90, a 10% loss of bending strength.
Step 5: Mount Fix the axle under the frame with U-shaped brackets carved from forked branches, or lash it firmly to the cross-member directly above it. The axle does not turn; the wheels turn on it.
Common Mistakes
- Softwood — wears through in days.
- Charring deeply — the lost diameter costs strength as the cube of the diameter.
- Journals sized for the new, not the worn state — the margin disappears as the bearing wears.
- Placing the linchpin hole inboard of the hub — it weakens the arm where the moment is greatest.
Safety
Fire and heavy timber
Charring journals means working beside a fire with a heavy beam; keep the work away from shavings and dry grass, and have water at hand. An axle lifted onto brackets can pinch hands, and an axle that breaks under a loaded cart drops the load, so test the finished cart at half load first.
What’s Next
- Learn next: Lubrication & Wear — keeping the journals alive
- Combine with: Axle Box & Bearings — the liner the journal runs in