Lantern Pinion
Part of Gear Making
Making and using the lantern pinion — the simplest gear form achievable with basic tools.
Why This Matters
The lantern pinion is one of the oldest and simplest gear forms ever developed. It consists of two parallel circular discs (end plates) connected by a series of cylindrical pins or rods, evenly spaced around the circumference. When a suitable mating gear (typically a wheel with pointed or rounded teeth, sometimes called a trundle gear or crown wheel) meshes with the lantern, the pins act as gear teeth, engaging the wheel teeth in sequence.
The lantern pinion can be made with no special gear-cutting equipment. The end plates need only drilled holes at equal angular spacing — achievable with compass layout and a drill. The pins are straight round rods cut to length and press-fitted or pinned into place. No tooth profile cutting is required. This makes the lantern pinion the first gear form accessible to a community just beginning to build mechanical power systems.
Lantern pinions powered the first mechanical clocks, water mills, and windmills throughout the medieval period. They are not as efficient or as quiet as well-cut involute gears, but they are far more buildable with primitive tools, and for the slow-speed, moderate-load applications of early machinery, they work perfectly well.
Geometry of the Lantern Pinion
A lantern pinion is characterized by:
Number of pins (staves): The number of cylindrical pins equals the number of teeth. Minimum practical is 6 pins; more common is 8–16 pins for small pinions. Fewer pins increase the variation in angular velocity (the kinematic error); more pins give smoother running.
Pin circle radius: The radius at which the pin centers are located. This determines the pitch circle of the lantern pinion.
Pin diameter: The pins must be strong enough to carry the tooth force. Pin diameter is typically 1/3 to 1/2 of the tooth pitch at the pitch circle.
Face width: The axial length of the pins (and the mating gear tooth width) determines the load capacity. Longer is stronger but increases the requirement for parallelism and alignment.
The equivalent module (a measure of tooth size) is approximately: m ≈ pin diameter × 2. The pitch (center-to-center tooth spacing at the pitch circle) equals π × m.
Making the End Plates
The end plates are circular discs with holes drilled at equal angular positions on a common pitch circle.
Marking out: Determine the required number of pins (staves) and the pitch circle radius. Use the compass method to divide the pitch circle into N equal parts — see the compass-arm article for the technique. Each division point is the center of one pin hole.
Drilling: Center-punch each point precisely. Drill with a drill slightly larger than the pin diameter (typically 0.5–1.0 mm larger) for a clearance fit, or at pin diameter for a push fit. All holes must be perpendicular to the plate face — use a drill guide or brace and bit held carefully vertical. Even 1–2 degrees of tilt changes the pin spacing and causes binding.
Squaring holes: For square or octagonal shafts (if available), make the center hole square — punch the hole round, then file it to the correct polygon.
Making and Fitting the Pins
Pins should be made from the hardest, straightest available material. Options in order of preference:
- Hardened and tempered iron or steel rod — best wear resistance
- Wrought iron rod, cold-drawn for straightness — adequate for moderate duty
- Hardwood dowels of dense, close-grained species (lignum vitae, boxwood, apple wood) — for very light duty at low speeds
Preparing pins: Cut all pins to the same length with a hacksaw or cold chisel. The length equals the gap between the inner faces of the end plates (the effective face width). Check length by standing all pins together and verifying they are the same height.
Fitting: Press pins into the end plate holes. If drilled at pin diameter, the fit should be snug — tap in with a hammer. If holes are 0.5 mm larger, secure with split pins, cotter pins, or by peening the rod end over a slight countersink.
Ensure all pins are perpendicular to the end plates and parallel to the central shaft. A simple checking jig — a flat board with a stop fence — helps maintain parallelism while pressing pins.
The Mating Wheel
The lantern pinion meshes with a wheel whose teeth engage the pins sequentially. The teeth of the mating wheel are rounded or pointed at the tips to reduce the width of contact and allow the pin to roll smoothly past the tooth.
Wheel tooth form for lantern mesh: The tooth flanks should be shaped as an epicycloid (the curve traced by a point on a circle rolling around another circle). For practical hand manufacture, a rounded tooth tip and flanks that blend smoothly from the root is adequate. The key requirement: the tooth is taller than the pin circle radius (the tooth root must clear the pins) and the tooth tip must clear the opposite end plate.
Tooth count for the wheel: The wheel should have significantly more teeth than the pinion has pins, for smooth operation and adequate gear ratio. A typical arrangement: 6–10 pin lantern pinion meshing with a 30–60 tooth wheel.
Applications and Limitations
Applications: Water mill drives (driving millstones through a gear train from a waterwheel), windmill drives, clock trains (early clock mechanisms used lantern pinions throughout), simple speed-increasing or reducing drives for hand machinery.
Limitations:
- Pin wear: the pins wear on their contact surface with the wheel teeth. For iron pins against iron wheel teeth, lubrication is essential to prevent rapid wear. Bronze pins in an iron wheel, or the reverse, extend life significantly.
- Speed limit: lantern pinions should not run above 1–2 m/s pitch line velocity without careful attention to lubrication and dynamic balance. Above this, the contact geometry causes shock loading.
- Noise: lantern pinions are noisier than involute gears due to less ideal contact geometry.
- Not suitable for reversing loads — the pins engage differently in each direction of rotation.
For a community just starting gear manufacture, the lantern pinion provides working machinery immediately. As metalworking skills develop, replace lantern pinions with cut gears wherever performance demands it.