Wallower and Spindle
Part of Mill Construction
The wallower is the gear that receives power from the pit wheel and transmits it to the vertical millstone spindle — the critical right-angle drive at the heart of the grain mill.
Why This Matters
The wallower is the highest-speed, most heavily loaded gear in a traditional grain mill. It runs continuously while the mill operates, turning at 10–15 times the speed of the water wheel, under the full torque needed to drive the millstones. It is the single component most likely to fail under heavy use, and its failure stops the mill immediately and completely.
Understanding the wallower — its construction, the geometric requirements for its proper meshing with the pit wheel, the bearing loads it imposes on the spindle, and the signs of wear — is essential for any community that operates a grain mill. The wallower is also the component most easily adjusted to change mill speed (by changing the number of staves), making it the practical “tuning” device for matching stone speed to different grain types or changing water conditions.
The spindle is equally important: a bent or worn spindle transmits vibration into the runner stone, causing uneven grinding and accelerating all wear throughout the mill. Keeping the spindle true and its bearings properly lubricated and adjusted is daily mill maintenance.
Wallower Design
The wallower is typically a lantern gear — not a solid gear wheel with cut teeth, but a cylinder formed by wooden or iron staves (pins) connecting two end discs. When viewed from the end, it looks like a cylindrical cage. The staves are the “teeth” that mesh with the cogs of the pit wheel.
This design has several advantages over solid wooden gears for this application:
- Staves can be individually replaced without removing the entire wallower
- The cylindrical shape allows the wallower to mesh with the pit wheel at the correct pitch point regardless of small alignment variations
- The open structure allows debris to fall through rather than jamming between teeth
- The end discs provide accurate geometry; stave dimensions are not critical if diameter and spacing are correct
Typical wallower dimensions for a 1.2m diameter stone:
- Diameter (pitch circle): 150–200mm
- Length (axial distance): 150–200mm (equal to or slightly greater than the face width of the pit wheel cogs)
- Number of staves: 8–12
- Stave material: dry, dense hardwood (apple, pear, hornbeam) or iron
- End disc material: hardwood or cast iron
The stave count determines the gear ratio with the pit wheel (see the Speed Ratios article). For most grain mills, 8 to 12 staves is the working range — fewer staves give higher speed (and more power per stave contact, increasing wear); more staves give lower speed with gentler loading.
Wallower Construction
End discs: Turned or carefully shaped to accurate circles. The bore (the central hole) must be exactly concentric with the outer diameter — any eccentricity causes the wallower to run unevenly, leading to rough meshing and vibration. The bore receives the spindle with a keyed fit.
Mark the stave hole positions around each disc using a dividing template (a disc with small nail holes at equal angular intervals). All stave holes must be at the same radial distance from the center and evenly spaced angularly. Any variation throws one stave farther from the center than the others, causing uneven tooth loading.
Staves: Turn or shape each stave to a consistent diameter (typically 30–50mm for a wood stave). The critical dimension is length — all staves must be identical in length, or the end discs will be tilted relative to each other.
Assembly: Press or drive the stave ends into the holes in the discs. The fit should be snug — the staves must not rock in their holes. Drive a small wooden wedge into a saw kerf at each stave end to lock it. Some builders add a light iron hoop around each disc to prevent the disc from splitting at the stave holes under load.
Key and keyway: The wallower must be keyed to the spindle to prevent rotation on the shaft. Cut a keyway in the wallower bore and on the spindle using a chisel; fit a hardwood or iron key. The key should be a firm drive fit — not so tight it splits the disc, not so loose it slips.
The Millstone Spindle
The spindle is the vertical shaft that connects the wallower (at its lower end, inside the gear pit) to the runner stone (at its upper end, in the milling chamber). It transmits the full torque needed to drive the stone.
Material: Iron is strongly preferred for the spindle. A wooden spindle can work for smaller mills but is prone to bending under the eccentric loads of the grinding process. An iron spindle maintains precision over years of use; a wooden one may need replacement every few years.
If making an iron spindle by forge work: the spindle is a bar of wrought iron, 40–60mm in diameter for a 1.2m stone, 1.0–1.5m long. It must be straight to within 1mm across its full length. Check straightness by rolling on a flat surface — any bend causes it to roll unevenly.
Taper: The upper end of the spindle is tapered (or has a specifically shaped top) to engage the mace (the iron bar that drives the runner stone). The exact profile depends on the mace design, but a squared top section with a tapered end is most common.
Bearing points: The spindle runs in two bearings:
- Footstep bearing (lower): supports the weight of the spindle and runner stone; sets the vertical position of the stone
- Neck bearing or bridge bearing (upper): a horizontal guide bearing that keeps the spindle vertical and centered in the eye of the bedstone
The footstep bearing takes axial (vertical) load; the neck bearing takes radial (horizontal) load. Both must be lubricated continuously during operation.
Bearing Materials and Lubrication
Footstep bearing: Typically a cast or forged iron cup with a hemispherical depression matching the rounded lower end of the spindle. The spindle tip rotates against the cup face — the contact area is small (just the rounded tip) to minimize friction torque. The cup must be harder than the spindle tip to avoid gouging.
Bronze footstep bearings (when available) are superior to cast iron — bronze is harder, has lower friction against iron, and tolerates occasional running dry better.
Neck bearing: A block of hard material (wood, stone, or metal) with a round hole slightly larger than the spindle. The spindle passes through loosely; the bearing prevents gross lateral movement but is not a tight fit. Hardwood boxes (a square block of close-grained hardwood bored to receive the spindle) are traditional and work well.
Lubrication schedule:
- Footstep bearing: apply tallow or lard every 4–6 hours of operation; check temperature every hour
- Neck bearing: apply tallow or lard every 8 hours; less critical than footstep
If a bearing runs hot (too hot to hold a hand on for more than a second), stop the mill immediately. The bearing is failing. Running a dry bearing to destruction ruins both the bearing and the spindle end.
Signs of Wallower and Spindle Wear
Wallower stave wear: Stave faces become convex and then flat as the cycloidal profile is worn away. This causes rough meshing — the drive becomes jerky rather than smooth. When stave contact surfaces show flat spots more than 5mm wide, it is time to replace those staves.
Uneven stave wear: If some staves wear faster than others, the wallower is off-center (eccentric). The faster-wearing staves are the ones projecting farther from the true center. Re-bore the wallower or shim the light staves to restore concentricity.
Spindle wear at bearing points: The spindle diameter at the neck bearing contact zone gradually decreases. Measure it periodically with calipers. When the diameter has reduced by 5% from the new dimension, the spindle should be trued and the bearing re-fitted, or the spindle replaced.
Spindle bend: A bent spindle shows up as regular vibration at the rotation frequency — a recurring thump or wobble synchronized with the stone revolution. Check by marking the spindle and observing whether the vibration peaks align with the mark. A bent spindle must be straightened (by heating and pressing) or replaced.