Make a wheel hub from a seasoned elm block turned to a cylinder 20-30 cm in diameter and 25-35 cm long, with a taper at each end, bored through the centre for the axle and mortised with one square hole per spoke. Elm is used because its interlocked grain resists splitting, and the design problem is leaving enough wood between the mortises to survive the driving of the spokes.
Part of Wheelwright Craft
The hub, also called the nave, is the centre block of a wheel that takes the axle at its bore and every spoke at its mortises.
The Hub Fails By Splitting Between Mortises
The hub carries the whole wheel load through a ring of square holes cut around its middle. Every spoke tenon is driven in tight, which pushes the wood outward like a wedge. If the web of wood between two mortises is too thin, the hub splits from one mortise to the next, and the wheel is lost. Elm is the choice because its interlocked grain resists that split better than oak or ash.
The ring of mortises takes up a lot of the hub. The carrier gives the tenon as 3 × 5 cm and a hub 20-30 cm across, but not which way round the tenon faces, so here are both:
| Hub diameter at the mortises | Circumference | 12 mortises 5 cm wide round the hub | 12 mortises 3 cm wide round the hub |
|---|---|---|---|
| 25 cm | π × 25 = 78.5 cm | 78.5 - 60 = 18.5 cm left, 1.5 cm per web | 78.5 - 36 = 42.5 cm left, 3.5 cm per web |
| 30 cm | π × 30 = 94.2 cm | 94.2 - 60 = 34.2 cm left, 2.9 cm per web | 94.2 - 36 = 58.2 cm left, 4.9 cm per web |
At 1.5 cm a web is dangerously thin. This is why wheels with 12 or more spokes use stagger, in which alternate mortises sit at different distances along the hub so the webs are not all in one ring (Engineering Principles), and why a larger hub is worth its weight.
What You Need
- An elm block at least 30 cm square and 35 cm long, air-dried 1-2 years (Wood Seasoning)
- Auger or large drill for the axle bore, and a mortise chisel and mallet
- A lathe if you have one, or a drawknife and spokeshave (Turning the Hub)
- A template of the finished profile, cut from a board
- Iron strap or hoop for the ends, if available
Method: Block To Finished Hub
Step 1: Choose the block Pick a block free of large knots and cracks, with its axis along the grain. A fresh crack at either end means more may come; discard it.
Step 2: Mark the axis and turn the outside Mark the axis at both ends and shape the cylinder with a taper at each end, keeping the centre marks (Turning the Hub).
Step 3: Bore from the centre marks Bore the axle hole from both ends toward the middle, using the marks so the bore is concentric with the turned outside. Every later step takes its reference from this bore, not from the rough surface.
Step 4: Mark the mortises Mark the belt where the spokes enter, divide the circumference equally, and mark the stagger. A 12-spoke wheel has mortises 30° apart; a 14-spoke wheel about 25.7° apart.
Step 5: Cut the mortises Cut each to the same size and the same outward tilt (Mortise Cutting).
Step 6: Line the bore Fit a box or sleeve (Axle Box & Bearings).
Step 7: Protect the ends Seal the end grain, and band the hub ends with iron if you can. Banding the hub ends with iron is traditional wheelwright practice, not stated in the parent article; it is intended to stop end splits.
Common Mistakes
- Mortising before boring — the mortises then reference the outside, not the axis, and the wheel runs eccentric.
- Too small a hub for the spoke count — the 12 mortises leave webs too thin to survive driving.
- Using unseasoned elm — the hub shrinks after the spokes are in, loosening every tenon.
- Leaving the end grain bare — end checks start there and run into the mortise belt.
Safety
Chisels and flying splinters
Mortising and boring put edged tools and a heavy block into a body-width work area. Clamp the block, keep both hands behind the cutting edge, cut away from your body, and wear eye protection when driving the mallet.
What’s Next
- Learn next: Turning the Hub — shaping the blank
- Combine with: Spoke Making & Fitting — the tenons that go into the mortises