A cam and disk intermittent drive converts continuous rotary input into stop-and-go output by riding a follower disk on a contoured cam — the cam profile pushes the disk through an index angle, then a circular dwell section holds it locked while the input keeps spinning. You see this exact mechanism inside Sankyo and CAMCO rotary index tables driving automotive assembly turrets. It exists because cycle time matters and dwell timing must be precise. A well-cut cam delivers indexing accuracy under ±30 arc-seconds at speeds up to 200 cycles per minute.
Continuous Rotary to Intermittent via Cam and Disk Interactive Calculator
Vary station count and cam timing angles to see the output index angle, dwell ratio, and intermittent motion.
Equation Used
The cam profile sets how much of each input revolution is spent indexing versus dwelling. For an evenly spaced follower disk, the output index per cycle is 360 divided by the number of stations. The dwell:index ratio compares the cam dwell arc to the cam rise/index arc.
- One cam revolution produces one index-and-dwell cycle.
- Follower disk stations are evenly spaced.
- Index cam angle is the rise portion of the cam profile.
How the Continuous Rotary to Intermittent via Cam and Disk Actually Works
The mechanism is built around two parts that look simple but hide all the engineering — a driving cam on the input shaft and a follower disk (sometimes a turret carrying rollers) on the output shaft. As the cam rotates continuously, a shaped rise section sweeps a follower roller, forcing the output disk to rotate through a defined index angle. Then the cam profile transitions into a concentric dwell arc — a section where the radius from the cam axis to the follower stays constant — and the output stops dead while the input keeps going. The ratio of dwell time to index time is set entirely by the cam profile, not by the speed.
Why build it this way instead of using a Geneva drive? Because the cam designer has full control over the acceleration curve. A modified-sine or modified-trapezoidal profile spreads acceleration smoothly across the index, peak torque drops, and you can run 3 to 5 times faster than a Geneva of the same size before vibration kills you. Globoidal (barrel) cams take this further by wrapping the followers around a hourglass-shaped cam — two rollers stay in contact at all times, so backlash is essentially zero.
Tolerances are unforgiving. The follower roller bore must match the spec exactly — if a 12.000 mm roller pin runs in a 12.05 mm bore instead of the required 12.005 mm fit, the roller skews under load and you hear a tick at every index. Cam profile errors above 5 µm cause repeatability drift you can measure on a turret. Common failure modes are roller spalling from over-preload, cam surface pitting from contamination in the oil bath, and follower-shaft fatigue cracking at the disk hub when shock loads exceed the rated indexing torque.
Key Components
- Driving Cam (Plate or Globoidal): The contoured input element. Plate cams use a face groove or rib; globoidal cams use a hourglass body wrapping the follower turret. Profile is ground to ±5 µm on production-grade indexers and case-hardened to 58-62 HRC for wear life beyond 10,000 hours.
- Follower Disk or Turret: Carries the cam-follower rollers — typically 4, 6, 8, or 12 evenly spaced around the output shaft. Roller count sets the index angle (360° / N). Disk runout must hold under 0.02 mm TIR or the rollers load unevenly.
- Cam-Follower Rollers: Crowned needle-bearing rollers ride the cam surface. Crown radius typically 200-500 mm to handle slight misalignment without edge-loading. Preload is set during assembly by adjusting an eccentric stud — too tight and you cook the bearings, too loose and the disk rattles at the dwell.
- Dwell Arc Section: The portion of the cam profile cut to constant radius from the input axis. While followers ride this section the output is mechanically locked. Dwell angle is typically 60-70% of the input revolution on a single-index cam, leaving 30-40% for the index motion itself.
- Output Shaft and Hub: Transmits indexed motion to the load. Hub is keyed and clamped to the disk; shaft sized for the inertial reaction torque, which on a modified-sine profile peaks at roughly 2× the steady-state torque needed to accelerate the load.
- Oil Bath Housing: The cam and rollers run submerged in ISO VG 220 gear oil. Oil level matters — below the lower follower and you spall the cam in 200 hours. Seal integrity at the output shaft is the #1 service item on a Sankyo or CAMCO unit.
Who Uses the Continuous Rotary to Intermittent via Cam and Disk
Cam and disk indexers show up wherever a machine has to advance a workpiece, dwell long enough for an operation, and repeat — fast and accurately. The mechanism dominates high-speed packaging, automotive assembly, and pharmaceutical filling because nothing else gives you that combination of cycle rate, indexing precision, and tunable acceleration profile. You'll find them rated for index loads from 5 kg up to 5,000 kg per station.
- Automotive Assembly: CAMCO 1100RDM rotary index tables driving 8-station turrets at Bosch fuel-injector assembly cells, indexing 45° at 60 cycles per minute with ±15 arc-second repeatability.
- Pharmaceutical Filling: Sankyo TR-style globoidal indexers powering 12-station vial-fill carousels on IMA Life freeze-dryer infeeds, holding each vial dead-still for 0.5 seconds during the fill nozzle stroke.
- Packaging: Weiss TC-150 ring indexers running cap-tightening turrets at 200 cycles per minute on Krones beverage lines, where Geneva drives cannot survive the inertial loads.
- Printing and Stamping: Bruderer BSTA high-speed stamping presses use cam-driven feed rolls to advance strip stock 25-100 mm per stroke at 1,500 strokes per minute.
- Electronics Assembly: Camcraft barrel-cam indexers driving connector pin-insertion turrets at TE Connectivity plants, indexing 30° per cycle with the dwell timed to allow a press-fit head to descend, seat, and retract.
- Food Processing: Tetra Pak A3/Flex carton-forming carousels use cam-disk drives to index aseptic carton blanks through the heat-seal stations at 24,000 packages per hour.
The Formula Behind the Continuous Rotary to Intermittent via Cam and Disk
The core question on any cam-disk indexer is: how long does the dwell last at a given input speed? That tells you whether your fill nozzle, weld head, or press tool actually has time to do its job. At the low end of typical operating range — say 30 RPM input — dwell is generous and your tooling has plenty of time, but throughput is poor. At the high end — 200 RPM and above — dwell shrinks to fractions of a second and you start fighting the operation cycle clock. The sweet spot for most production indexers sits between 60 and 120 RPM, where dwell time is long enough for the work and cycle rate justifies the machine.
Variables
| Symbol | Meaning | Unit (SI) | Unit (Imperial) |
|---|---|---|---|
| tdwell | Time the output disk is stationary per cycle | s | s |
| θdwell | Dwell angle ground into the cam profile | ° | ° |
| Nin | Input cam shaft rotational speed | RPM | RPM |
| tindex | Time for the output to move through one index step | s | s |
| θindex | Index angle of the cam (360° − θdwell) | ° | ° |
Worked Example: Continuous Rotary to Intermittent via Cam and Disk in a snack-bar wrapping carousel
You are specifying a cam and disk indexer for an 8-station snack-bar wrapping carousel on a Bosch Sigpack HBM line. The cam is cut with a 240° dwell and 120° index, giving the wrap, fold, seal, and discharge stations time to do their work while the carousel is locked. You need to know the dwell window at the line's nominal cam speed of 90 RPM, and how that window changes if production pushes the line to 150 RPM or backs it off to 45 RPM during ramp-up.
Given
- θdwell = 240 °
- θindex = 120 °
- Nnom = 90 RPM
- Nlow = 45 RPM
- Nhigh = 150 RPM
Solution
Step 1 — at the nominal 90 RPM line speed, find the cycle time:
Step 2 — apply the dwell-fraction to compute nominal dwell time:
That is the window your seal-jaw, fold-plate, and discharge pusher all have to complete their stroke. 0.444 s is comfortable for a 30 mm seal-jaw stroke at typical pneumatic speeds — you can fit the descend, dwell-on-seal, and retract phases inside it without rushing.
Step 3 — at the low end, 45 RPM during ramp-up:
Almost double the nominal window. The tooling barely notices — but throughput halves, so this is only acceptable as a startup or jam-clear speed.
Step 4 — push to the high end, 150 RPM:
That is tight. A standard 30 mm seal-jaw stroke at 0.5 m/s takes 0.060 s each way, leaving only 0.147 s for the actual heat-seal contact. If your seal needs 0.2 s of jaw contact to fuse the film properly, you'll see weak seals above ~120 RPM. This is the classic ceiling — the indexer can run faster, but the operation can't.
Result
Nominal dwell at 90 RPM is 0. 444 s — a healthy window for a typical heat-seal-and-fold operation on a snack bar wrapper. Pulling back to 45 RPM stretches dwell to 0.889 s and pushÂing to 150 RPM compresses it to 0.267 s, so the practical sweet spot for this 240°-dwell cam sits between 80 and 120 RPM where seal quality and cycle rate both stay healthy. If you measure dwell shorter than predicted on a real machine, the most common causes are: (1) cam-follower preload set too tight, which adds a fraction of a degree of cam wind-up at index entry and effectively eats dwell, (2) input servo not actually holding commanded RPM under load — check encoder feedback against the nameplate, and (3) cam profile worn at the dwell-to-index transition, which rounds the corner and shortens the locked window by 2-3°.
When to Use a Continuous Rotary to Intermittent via Cam and Disk and When Not To
Cam and disk indexers compete head-on with Geneva drives and servo-driven index tables. The choice comes down to cycle rate, indexing accuracy, and how much money the application can spend. Here's how the three stack up on the dimensions that actually matter when you're sizing an indexer.
| Property | Cam and Disk Indexer | Geneva Drive | Servo-Driven Index Table |
|---|---|---|---|
| Max practical cycle rate | Up to 300 cycles/min on globoidal designs | 60-90 cycles/min before vibration kills accuracy | 200+ cycles/min, limited by motor and inertia |
| Indexing accuracy | ±15 to ±30 arc-seconds | ±2 to ±5 arc-minutes (10× worse) | ±5 arc-seconds with feedback, drifts without |
| Dwell-to-index ratio control | Fully tunable via cam profile (60/40 to 80/20) | Fixed by slot geometry — no adjustment | Fully programmable in software |
| Capital cost (8-station, 50 kg load) | $8,000-$18,000 | $2,000-$5,000 | $12,000-$30,000 with drive and controls |
| Service life before rebuild | 10,000-20,000 hours in oil bath | 5,000-15,000 hours on greased pin | Indefinite — wear is in the bearings, not motion mechanism |
| Backlash at output | Near-zero on globoidal (dual-roller contact) | Slot-to-pin clearance, 5-30 arc-min | Depends on gearbox — cycloidal can hit 1 arc-min |
| Application fit | High-speed packaging, assembly, filling | Slow-cycle, cost-sensitive indexing | Variable-program flexible automation |
Frequently Asked Questions About Continuous Rotary to Intermittent via Cam and Disk
Ringing during the index phase but silence on dwell points to acceleration-induced vibration in the follower train, not cam wear. The cam profile transitions through peak acceleration roughly 25% into the index motion — if the output disk inertia plus load inertia exceed what the cam designer assumed, the follower roller momentarily unloads at the inflection points and you hear that as a chatter.
Two checks: weigh the actual load on the disk and compare against the indexer nameplate inertia rating. Then verify follower preload — back the eccentric studs off until you see 0.05 mm of roller play, then snug them just enough to remove it. Over-preloading does not fix chatter, it just trades audible noise for accelerated bearing wear.
Station count drives the index angle (360°/N) and therefore the cam's peak acceleration. Fewer stations means a larger jump per cycle, higher peak acceleration, and more violent torque spikes — a 4-station disk indexes 90° per cycle and hits roughly 2.5× the peak inertial torque of an 8-station disk indexing 45° at the same RPM.
Rule of thumb: pick the highest station count that still gives each station enough physical space for its tooling. If your fill nozzle needs 200 mm of clearance and your disk is 600 mm diameter, 8 stations works (235 mm pitch). Going to 6 stations to ease the cam loading buys you a quieter machine but costs you 25% throughput.
That's a 4× degradation, and it almost never comes from the cam itself unless it's been damaged. Check three things in order: first, the output coupling between the indexer hub and your load — a keyed connection with a sloppy fit gives you exactly this kind of repeatability loss. Use a shrink-disk or tapered hub instead.
Second, check the load mounting concentricity. If the dial plate runs out 0.1 mm at 300 mm radius, that's 1.1 arc-minutes of apparent error baked into the geometry. Third, oil temperature — a cold indexer at startup runs tighter than at thermal equilibrium because the housing aluminium expands. Always measure accuracy after a 30-minute warm-up.
Yes, but carefully and slowly. The cam profile is symmetric for reverse motion, but the follower preload is typically set with a slight bias toward the forward-drive side. Reversing under load can momentarily unload the trailing roller and allow the disk to backlash by an arc-minute or two before the opposite roller takes up.
The practical rule: reverse only at jog speed (under 5 RPM input), only with the load disengaged or unclamped, and only far enough to clear the obstruction. Do not run a production cycle in reverse — you'll wear the off-side rollers unevenly and the indexer will lose its forward-direction accuracy within a few hundred hours.
It sees both, and you must size for the peak. Steady-state torque on the input shaft is just the friction load — typically 5-10% of the indexer's rated capacity. But during the index motion, the cam transmits the inertial torque required to accelerate the load, and on a modified-sine profile that peaks at roughly 2× the average index torque.
Sizing rule: calculate the average index torque from load inertia × peak angular acceleration, multiply by 2 for profile peak, then add 30% margin for friction and oil shear. A continuous-duty motor rated at the average will overheat; you want a motor whose intermittent or peak rating covers the spike, with continuous rating above the steady friction load.
The output shaft seal sees something the test rig didn't — an external radial load from your dial plate and tooling. Side load on the output shaft tilts the shaft inside the seal lip by a few microns, and that flexes the lip outward on every revolution until it loses interference and starts weeping.
Check the radial load against the indexer's published output-shaft load rating. If you're over, you need an outboard support bearing on the dial plate to take the side load off the indexer shaft. Sankyo and CAMCO both publish radial-load curves for their units — running at 80% of the rated radial load roughly halves seal life compared to running at 30%.
References & Further Reading
- Wikipedia contributors. Cam (mechanism). Wikipedia
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