A single-tooth driving wheel and notched wheel is an intermittent motion mechanism where a driver carries one tooth (or pin) that engages a slotted or notched follower exactly once per revolution of the driver, advancing the follower by one increment and then dwelling. It solves the problem of converting continuous rotation into reliable single-step motion without a clutch or solenoid. Each driver revolution produces one count, so a 10-notch follower needs 10 driver turns to complete a full revolution. You see this in odometers, postage meter digit drums, and pinball score reels.
Single-tooth Driving Wheel and Notched Wheel Interactive Calculator
Vary the follower notch count and driver speed to see step angle, count rate, average follower speed, and the intermittent indexing motion.
Equation Used
This calculator uses the basic single-tooth indexing relationship: each driver revolution advances the notched follower by one notch. With N equally spaced notches, the angular step is 360/N, the follower needs N driver turns for one full revolution, and the count rate equals the driver rpm.
- One driver tooth advances exactly one follower notch per driver revolution.
- Follower notches are equally spaced.
- No missed engagement, slip, backlash, or overshoot is included.
- Follower rpm is the average speed; actual motion is intermittent with dwell.
How the Single-tooth Driving Wheel and Notched Wheel Actually Works
The driving wheel carries a single tooth on its outer rim. The notched wheel — sometimes called a count wheel — has equally spaced notches around its circumference, with a smooth locking arc filling the space between each notch. As the driver rotates continuously, the lone tooth sweeps past the locked dwell zone doing nothing, then catches the leading flank of the next notch, drives the follower forward by exactly one notch pitch, and disengages. The rest of the driver's revolution is dead time — the locking arc on the driver rides against the smooth land of the follower, holding it stationary. That dwell-hold is the whole point. It is the same intent as a Geneva drive, just simpler and with a much higher dwell-to-motion ratio.
Geometry is unforgiving here. The tooth tip must clear the locking land by 0.1 to 0.3 mm — too tight and you get binding and stalled motors, too loose and the follower drifts under vibration and you lose count. If the tooth engages the notch flank too early, the follower jerks and overshoots; too late, and you get incomplete advance with the digit drum reading half a position. On a typical brass-on-brass count wheel running at 60 RPM driver speed, the engagement window is around 30 to 40 ms. Miss the timing by 5° of driver rotation and the follower will skip or stutter.
Common failures: a worn tooth tip rounds off and the follower under-rotates by a few degrees per cycle, which compounds into a missed count after 20 or 30 cycles. A bent locking arc lets the follower creep — you'll see digits drift between counts. And if the driver-to-follower centre distance opens up by more than about 0.15 mm due to bushing wear, engagement becomes inconsistent and you get random skips.
Key Components
- Driving Wheel (Single-tooth Driver): A disc carrying one tooth or pin on its rim, with the remaining circumference machined as a smooth locking arc. Typical tooth height is 1.5 to 4 mm depending on follower notch depth. The tooth profile is usually a modified involute or a simple radial pin in low-cost builds.
- Notched Wheel (Count Follower): A wheel with N evenly spaced notches around its rim, separated by smooth locking lands. N sets the step ratio — a 10-notch wheel advances 36° per driver revolution. Notch flank angle is typically 20° to 30° to allow clean entry without binding.
- Locking Arc / Dwell Land: The smooth circumferential surface on the driver that rides against the follower's land during the dwell phase. Radial clearance is held to 0.1 to 0.3 mm. This is what holds the follower locked between counts — without it the follower would coast under inertia.
- Centre Distance Bushings: Bronze or sintered bronze bushings supporting the driver and follower shafts. Centre distance tolerance is typically ±0.05 mm. Wear that opens this distance beyond 0.15 mm causes skipping or false counts.
- Carry Pawl (optional): Used in multi-digit counter stacks where the units digit's notched wheel itself carries a single tooth that drives the tens-digit notched wheel once per full revolution — propagating a carry. This is how mechanical odometers and the Veeder-Root counter family work.
Industries That Rely on the Single-tooth Driving Wheel and Notched Wheel
You find this mechanism wherever someone needs cheap, reliable, one-step-per-revolution counting without electronics. It is mechanically simpler than a Geneva drive — only one tooth instead of a full driving crank — which is why it dominates low-cost counter applications. The trade is speed: it doesn't handle high-RPM indexing well because the engagement is impulsive rather than smoothly accelerated. Below 200 RPM driver speed it runs for decades; push past 400 RPM and the tooth flank fatigues quickly.
- Office equipment: Veeder-Root mechanical tally counters use stacked single-tooth driver and notched-wheel pairs to propagate carries between digit drums.
- Automotive instrumentation: Pre-1990s mechanical odometers in vehicles like the VW Beetle and Ford Cortina used a single-tooth carry between each tenth-of-a-mile drum.
- Postage and mailing: Pitney Bowes Model 5300 postage meter impression counters advance the units digit drum by one notch per print cycle using a single-tooth driver.
- Amusement and arcade: Gottlieb and Bally electromechanical pinball score reels of the 1960s and 70s — including the Sing Along backbox — used a solenoid-pulsed single-tooth driver against a 10-notch wheel.
- Industrial production counting: Press stroke counters on Bruderer and Schuler stamping presses register each cycle through a cam-driven single-tooth advance.
- Water and gas metering: Neptune T-10 residential water meter register stacks use single-tooth-and-notched-wheel carries to propagate counts across gallon, hundred-gallon, and thousand-gallon dials.
The Formula Behind the Single-tooth Driving Wheel and Notched Wheel
What you actually need to know is how many driver revolutions it takes to complete one full follower revolution, and how fast the follower indexes given a continuous driver speed. At the low end of the typical operating range (around 10 to 30 RPM driver speed), engagement is leisurely and even a worn tooth advances the notch cleanly — this is where 50-year-old odometers still work. At the nominal 60 to 120 RPM range, you sit in the sweet spot for postage meters and tally counters. Push past 300 RPM and impulsive engagement starts hammering the tooth root, and you'll see fatigue cracks within months.
Variables
| Symbol | Meaning | Unit (SI) | Unit (Imperial) |
|---|---|---|---|
| ωfollower | Angular speed of the notched (follower) wheel, averaged over one driver revolution | rev/s or rad/s | RPM |
| ωdriver | Angular speed of the single-tooth driver | rev/s or rad/s | RPM |
| N | Number of notches on the follower wheel | dimensionless count | dimensionless count |
| θstep | Angular step per driver revolution = 360° / N | degrees or radians | degrees |
Worked Example: Single-tooth Driving Wheel and Notched Wheel in a brewery keg-fill cycle counter
Sizing a single-tooth driver and 10-notch count wheel for a small craft brewery in Victoria BC that wants to log keg-fill cycles on a refurbished GAI 3001 isobaric filler. The filler completes one fill cycle every 4 seconds at full production rate. A cam on the fill carousel rotates the driver once per fill cycle, and the notched wheel drives a 4-digit Veeder-Root style register. You need to confirm step rate, full-revolution time of the units drum, and that the engagement geometry survives a 10-hour shift.
Given
- Cycle time = 4 seconds per fill
- N = 10 notches
- θstep = 36 degrees
- Shift length = 10 hours
Solution
Step 1 — convert the nominal 4-second cycle time into driver speed:
Step 2 — compute the average follower speed at nominal cycle rate:
That means the units digit drum completes a full revolution every 40 seconds at full production rate — comfortable, well within the cheap brass-on-brass durability envelope.
Step 3 — at the low end, when the line idles at one fill every 12 seconds (5 RPM driver), the follower averages:
The units drum takes 2 minutes per revolution. Engagement is slow and gentle. You can hand-cycle the mechanism and watch each step register cleanly.
Step 4 — at the high end, if a future packaging upgrade pushes cycle time down to 1.5 seconds (40 RPM driver):
Each step now happens every 1.5 seconds. The units drum spins once every 15 seconds. This is still safe for a hardened steel tooth, but a sintered bronze driver tooth would start showing flank wear within 6 months at this duty.
Step 5 — total counts per shift at nominal rate:
Result
At nominal 4-second cycle time the follower averages 1. 5 RPM, the units drum completes a full revolution every 40 seconds, and the register tallies 9,000 fills across a 10-hour shift. The low-end idle case at 0.5 RPM follower speed is so slow you can verify each count by eye, while the high-end 4 RPM case is the upper limit before you should swap to a hardened steel driver tooth. If the register reads short by 1 to 2 counts per hour, the most common causes are: (1) the driver tooth engaging the notch 2-3° early because of a worn cam follower on the carousel, causing partial advances, (2) a rounded tooth tip from sintered-bronze wear leaving the follower under-rotated by 4-5° per cycle until eventually a count is dropped entirely, or (3) the follower's locking land glazed with brewery sugar residue, increasing dwell friction and stalling the next engagement.
Single-tooth Driving Wheel and Notched Wheel vs Alternatives
Single-tooth-and-notched-wheel is one of three common ways to convert continuous rotation into one-step-per-revolution intermittent motion. The other two you'll see in the same applications are the Geneva drive and the ratchet-and-pawl. Pick based on speed, dwell precision, and how forgiving you need the geometry to be.
| Property | Single-tooth Driver & Notched Wheel | Geneva Drive | Ratchet & Pawl |
|---|---|---|---|
| Practical max driver speed | ~300 RPM before tooth fatigue | ~600 RPM with hardened pin and slot | ~1200 RPM (limited by pawl bounce) |
| Indexing accuracy | ±1° (notch flank dependent) | ±0.1° (geometric, very precise) | ±2° (pawl seat variability) |
| Dwell-to-motion ratio per cycle | ~95% dwell, 5% motion | ~75% dwell, 25% motion (4-slot) | Variable — driver-controlled |
| Manufacturing cost | Lowest — two simple turned discs | Moderate — slotted star + crank pin | Low — but needs a spring |
| Load capacity at follower | Low to moderate (~5 Nm) | Moderate to high (~50 Nm) | Low (limited by pawl tooth) |
| Service life at typical duty | 10+ years at <100 RPM, brass | 20+ years, hardened steel | 5-15 years, spring fatigue limited |
| Best application fit | Mechanical counters, score reels, registers | Indexing turrets, film advance, machine tools | Hand tools, hoists, one-way drives |
Frequently Asked Questions About Single-tooth Driving Wheel and Notched Wheel
Skipping under variable speed almost always means the engagement window is timing-sensitive. The single tooth has only one shot at catching the notch flank per driver revolution. If the driver decelerates mid-engagement (common when a cam-driven driver shares load with another mechanism), the tooth can lose contact with the flank before the follower has rotated through the full 36° step.
Diagnostic check — slow the system down to a quarter speed and watch the engagement. If the follower advances cleanly at low speed but skips at full speed, the issue is dynamic, not geometric. Add a small flywheel to the driver shaft to even out the angular velocity, or move to a notch flank with a steeper entry angle (20° instead of 30°) so the tooth captures earlier in the cycle.
The deciding factor is dwell ratio. A single-tooth driver gives you about 95% dwell — the digit drum is locked stationary for 95% of the driver's revolution. A 4-slot Geneva only gives 75%. If your downstream process (printing, sensing, photographing the digit) needs a long stable dwell relative to the index event, single-tooth wins.
Geneva wins when you need precision and load capacity. The Geneva slot constrains the follower geometrically through the entire engagement, so the index angle is exact. The single-tooth depends on the notch flank pulling the follower into position, which is fine for visual digit display but inadequate for, say, a turret indexing a cutting tool.
You are seeing notch flank slip-off. The follower stops rotating the moment the driver tooth disengages from the trailing edge of the notch flank. If the tooth tip is rounded (worn or under-machined) it disengages slightly before reaching the geometric end-of-step, leaving the follower 0.5 to 1.5° short.
Check the tooth tip radius first. A fresh tooth should have a tip radius under 0.2 mm. Anything over 0.5 mm starts robbing degrees from the step. The fix is to replace the driver — re-grinding the tooth shortens the engagement reach and makes the problem worse.
Yes, this is exactly how multi-stack carry mechanisms work in odometers, but only if the second follower's notch is angularly offset from the first by half a tooth-width minimum. If both notches present at the same angle, the tooth contacts both simultaneously and the load doubles on the tooth root — fatigue life roughly halves.
The clean approach is to use a single tooth with two notched wheels stacked axially, each notch indexed 18° off the other (for 10-notch wheels). One advances on the leading flank, the other on the trailing flank, distributing the impulse and giving you two outputs per driver revolution.
Creep during dwell is almost always a centre-distance problem. The locking arc on the driver is supposed to ride against the smooth land between notches with around 0.1 to 0.3 mm clearance. If the bushings have worn and the centre distance has opened up by 0.2 mm or more, the locking arc no longer fully constrains the follower and any vibration or downstream torque load can rotate it a few degrees.
Measure the centre distance with the system at rest. If it's outside the original spec by more than 0.15 mm, replace the bushings before doing anything else. People often blame the locking arc surface finish, but it's almost always the bores.
Around 300 RPM driver speed for a brass-on-brass system, 500 RPM for hardened steel. The limit is impulsive engagement — the single tooth slams into the notch flank at full driver velocity, and the impact stress at the tooth root scales with the square of the angular velocity. Brass yields under repeated impact above 300 RPM and you'll see flank deformation within weeks.
If you need higher speeds, the Geneva drive accelerates and decelerates the follower smoothly through the engagement curve, eliminating the impulse. That is why high-speed packaging machines and stamping presses use Geneva, not single-tooth.
References & Further Reading
- Wikipedia contributors. Intermittent mechanism. Wikipedia
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