A globoid cam is a rotating hourglass-shaped cam with a helical rib cut into its concave outer surface that engages cam followers mounted radially on a driven turret. The rib is the working component — it contacts two followers at once, preloading them against each other to give zero backlash. The mechanism converts continuous input rotation into precise intermittent or continuous indexed output rotation. You see it driving rotary index tables on Sankyo and Ferguson indexers at speeds up to 2,000 indexes per minute with positional repeatability inside ±30 arc-seconds.
Globoid Cam Interactive Calculator
Vary the rib-to-follower gap and tolerance limits to see preload, free clearance, repeatability, and backlash risk.
Equation Used
The calculator treats the measured rib-to-follower gap as the controlling tolerance. A negative gap is preload, which removes play between the two followers and the rib. A positive gap is free clearance; once it approaches the slack limit, the zero-backlash behavior is lost. The repeatability value is carried through as the positioning reference from the mechanism description.
- Gap g is measured cold at the rib-to-follower contact.
- Negative gap means preload or interference; positive gap means free clearance.
- Clearance at or above the slack limit indicates loss of zero-backlash behavior.
- Repeatability is shown as the selected positioning error reference.
How the Globoid Cam Works
A globoid cam — sometimes called an hourglass cam or roller gear indexer — has a body shaped like an hourglass with a single or double helical rib wrapped around its concave waist. A turret carrying evenly spaced cam follower rollers sits perpendicular to the cam axis, and as the cam rotates the rib pushes one follower while a second follower stays in contact on the opposite side of the rib. That dual contact is the whole reason the mechanism exists. You preload one follower against the other across the rib thickness and the result is zero backlash — the turret cannot rattle, drift, or overshoot under load.
The rib profile dictates everything. Through the dwell zone the rib runs purely circumferentially, so the turret holds station while the cam keeps rotating. Through the index zone the rib pitches axially along the cam, driving the next follower into the next station. Engineers cut the index zone with a modified-sine or modified-trapezoid motion law to keep peak acceleration and jerk inside the load limit of the bearings. Get the profile wrong and you'll feel it — a poorly blended dwell-to-index transition rings the turret like a bell at every cycle, and the followers brinell within months.
Tolerances are tight. The rib-to-follower clearance on a Sankyo or CAMCO indexer is typically set at 0 to -0.005 mm preload, measured cold. Slack above 0.01 mm and you lose the zero-backlash property — the turret starts to wander during dwell under reaction torque from whatever the table is carrying. Run too much preload and the cam-follower needle bearings fail by overheating long before their rated L10. Both followers and rib are case-hardened to HRC 58-62 and ground; if you spot pitting on the rib face the usual cause is contaminated lubricant or a follower that locked up and slid instead of rolling.
Key Components
- Globoid (hourglass) cam body: The concave rotating drum carrying the helical rib. Typical face widths run 80-300 mm depending on turret diameter, and the body is ground after heat treatment to hold rib-position accuracy inside ±0.005 mm across the full helix.
- Helical rib (cam track): The raised working surface that contacts the followers. Profiled with a modified-sine motion law for indexes up to 1,200 per minute, modified-trapezoid above that. Rib face hardness HRC 58-62, ground finish Ra ≤ 0.4 µm.
- Cam follower rollers: Needle-bearing studs mounted radially on the turret face, usually 6, 8, 12, 16, or 24 followers depending on index count. Roller OD must match the rib slot to a -0.005 mm preload — not zero, not -0.01 mm.
- Turret (output flange): The driven plate that carries the followers and the payload. Runout under 0.01 mm TIR at the tool face is standard on a CAMCO 902RDM-class indexer.
- Cam-shaft bearings: Usually a matched pair of angular-contact bearings preloaded to handle the axial reaction from the helical rib. Failure here shows up as cyclic positioning error synchronised with cam rotation.
- Housing and oil bath: Cast-iron housing holding an oil bath that splash-lubricates the rib and followers. Oil level matters — half a litre low and the upper followers run dry through the dwell.
Industries That Rely on the Globoid Cam
Globoid cams sit at the heart of any high-speed indexed assembly or packaging line where you need precise stops, zero backlash, and the ability to take reaction torque from the payload during dwell. They show up wherever a rotary table moves discrete parts station-to-station faster than a servo can do it economically. The advantage over a servo-driven indexer is mechanical certainty — the cam profile guarantees a repeatable motion law every cycle, no PID tuning, no following error, no thermal drift in the controller.
- Pharmaceutical packaging: Rotary tablet press infeed turrets on Fette and Korsch presses use globoid cam indexers to position dies under the punch with ±15 arc-second repeatability.
- Automotive assembly: Sankyo roller gear indexers drive the rotary dial tables on Bodine and AGI multi-station assembly machines building fuel injectors and ignition coils.
- Beverage filling: Krones and Sidel filler-capper monoblocs use globoid-driven star wheels to transfer bottles between filler and capper at 60,000 bph.
- Machine tools: Tool-changer carousels on Mazak and Okuma machining centres index tool pots with a globoid cam to hit ±30 arc-second positioning under the swing load of a 25 kg tool holder.
- Electronics assembly: CAMCO 601RDM indexers drive the part-feed dials on Universal Instruments through-hole insertion machines.
- Cosmetics and personal care: Rotary lipstick fill-and-cap lines from Dara and Marchesini use globoid cam indexers to step containers through fill, flame-pass, and cap stations.
The Formula Behind the Globoid Cam
The single most useful calculation for a globoid cam indexer is the peak follower acceleration during the index zone, because that number sets the bearing life of the cam followers and tells you whether your payload inertia will survive the cycle. At the low end of the typical operating range — say 30 indexes per minute on a slow assembly dial — peak acceleration is gentle and you can throw bigger payloads at the table than the cam is rated for. At the nominal design speed the cam profile delivers its rated peak. Push past nominal and the acceleration scales with the square of speed, which is where most users get caught — doubling the index rate quadruples the dynamic load on the followers and slashes the L10 life of the bearings.
Variables
| Symbol | Meaning | Unit (SI) | Unit (Imperial) |
|---|---|---|---|
| apeak | Peak tangential acceleration of the follower during the index zone | m/s² | in/s² |
| Cm | Motion-law coefficient (4.888 for modified sine, 4.888 for cycloidal, 5.528 for modified trapezoid) | dimensionless | dimensionless |
| h | Stroke (rise) of the follower during one index — the linear distance the follower travels along the rib | m | in |
| ωcam | Cam shaft angular velocity | rad/s | rad/s |
| β | Index-zone cam angle (the portion of one cam revolution during which the follower is moved) | rad | rad |
Worked Example: Globoid Cam in an 8-station rotary capsule-checkweigher dial
You are sizing the globoid cam indexer for an 8-station rotary capsule-checkweigher dial on a Bonfiglioli pharma line. The turret diameter is 400 mm, so each follower sits at 200 mm radius. The job calls for 60 indexes per minute nominal, with the customer asking what happens at 30 ipm (slow validation runs) and 120 ipm (planned future capacity bump). The cam uses a modified-sine motion law (C<sub>m</sub> = 4.888), a 270° dwell and 90° index split (β = π/2 rad), and stroke h = 2π × 0.200 / 8 = 0.157 m per index.
Given
- Stations = 8 —
- Turret radius = 0.200 m
- Stroke h = 0.157 m
- Motion coefficient Cm = 4.888 —
- Index angle β = π/2 = 1.571 rad
- Nominal index rate = 60 ipm
Solution
Step 1 — convert the nominal 60 indexes per minute to cam shaft angular velocity. One full cam revolution produces one index, so:
Step 2 — plug into the peak-acceleration formula at nominal speed:
That's about 1.25 g at the follower. On a 400 mm turret carrying 8 capsule nests at perhaps 0.5 kg each plus the dial itself, that acceleration is comfortable — well inside the dynamic load rating of an INA KR22 cam follower running on a CAMCO-class indexer.
Step 3 — at the low end of the operating range, 30 indexes per minute, ωcam halves and acceleration drops with the square:
That's 0.3 g — barely enough to spill water from a glass on the dial. At validation-run speed the followers are loafing and bearing life is essentially unlimited.
Step 4 — at the high end, 120 indexes per minute:
That's 5 g at the follower. The dynamic radial load on the cam follower roughly quadruples versus nominal — and because cam-follower L10 fatigue scales with the cube of load, your bearing life drops by a factor of roughly 64 going from 60 to 120 ipm. The capsule nests will also start lifting if they aren't positively retained, and you'll hear the turret ring during each dwell-to-index transition because the rib-follower preload is no longer enough to keep both followers loaded under the dynamic reaction.
Result
Peak follower acceleration at the nominal 60 ipm design point is 12. 3 m/s² (about 1.25 g). At that level the indexer runs quietly, the followers stay loaded across both faces of the rib, and a CAMCO 902RDM-class unit will hit its rated 20,000-hour L10 with the standard oil bath. Drop to 30 ipm and acceleration falls to 3.07 m/s² — almost imperceptible, completely benign for the followers; push to 120 ipm and you're at 49.2 m/s² with bearing life dropping roughly 64-fold, which is the classic mistake operations teams make when they assume "the cam can handle it." If you measure cycle-to-cycle position scatter above ±30 arc-seconds at the tool face, the usual culprits are: (1) cam-shaft bearing preload lost, letting the cam float axially during the index transition; (2) follower stud loosening on the turret because the threadlock failed under reverse torque at dwell-to-index transition; or (3) oil level dropped below the lower rib face, so the upper followers ran dry and brinelled the rib. None of these are catastrophic alone, but stack two of them and you'll see visible turret oscillation at dwell.
When to Use a Globoid Cam and When Not To
The globoid cam isn't the only way to index a rotary table. Its real competition is the Geneva drive on the low end and the servo-driven indexer on the high end. Each wins on a different axis — speed, cost, accuracy, or flexibility — and picking the wrong one costs you either money or production rate.
| Property | Globoid Cam Indexer | Geneva Drive | Servo Indexer |
|---|---|---|---|
| Max indexes per minute | Up to 2,000 ipm | Up to 200 ipm | Up to 300 ipm under load |
| Positional repeatability | ±15 to ±30 arc-sec | ±2 to ±5 arc-min | ±10 to ±60 arc-sec (depends on encoder + brake) |
| Backlash | Zero (preloaded conjugate followers) | Present at engagement | Depends on gearbox — 1 to 5 arc-min typical |
| Motion law flexibility | Fixed at manufacture (mod-sine, mod-trap, cycloidal) | Fixed by geometry (sinusoidal-ish) | Fully programmable |
| Capital cost (8-station, 400 mm turret) | $8,000-$18,000 | $1,500-$4,000 | $12,000-$25,000 with drive and brake |
| Lifespan / L10 | 20,000-40,000 hours | 5,000-15,000 hours | Limited by gearbox/brake, often 15,000 hours |
| Best application fit | High-speed, fixed-cycle assembly and packaging | Low-speed, low-cost intermittent motion | Variable-station, recipe-driven lines |
Frequently Asked Questions About Globoid Cam
Thermal growth. The cam body and turret housing run cooler at startup than the cam shaft and bearings, and the assembly walks axially by 5-15 µm as it heats. If the cam-shaft bearing preload was set on the loose side of spec the cam now drifts axially through each index, and you see the scatter as a drift in dwell position — not random noise but a slow walk over the warm-up hour.
Diagnostic check: clamp a dial indicator on the cam-shaft end face and watch axial movement from cold to operating temperature. Anything over 0.02 mm means the angular-contact bearings need re-preloading or replacement.
If the recipe changes the number of stations or the dwell-to-index ratio, go servo. The globoid cam is profiled at manufacture — you cannot change index angle, dwell angle, or motion law without buying a new cam. If the recipe only changes what happens at each station (different tool, different fill volume) but the index pattern stays the same, the globoid wins on speed, repeatability, and bearing life.
Rule of thumb: more than two distinct index patterns over the machine's life means servo. One pattern forever means globoid.
Two effects stack. First, real motion laws aren't perfectly cut — manufacturing tolerance on the rib profile adds 5-10% peak acceleration above the theoretical. Second, an accelerometer mounted on the turret picks up structural ringing at the dwell-to-index and index-to-dwell transitions, which superimposes a high-frequency spike on the smooth cam profile. Filter the signal at 10× the index rate and the measured peak should drop within 10% of theoretical.
If after filtering you're still 30% high, the cam is out of profile — usually from a follower that locked and skidded, leaving a flat on the rib.
Sometimes, but check the cam-shaft bearings and the housing oil capacity first. Doubling speed quadruples follower load and roughly doubles heat input. The original bearings may not be rated for the new dynamic load and the oil bath may not have enough volume to dissipate the heat. On a CAMCO or Sankyo unit the manufacturer will tell you the maximum cam profile that ships in a given housing — exceed it and you'll cook the oil within months.
The cleaner path is usually to buy the next housing size up rather than over-driving the existing one.
You've lost the conjugate preload. The zero-backlash property only holds when both followers are pinched against the rib at the same time. If the rib-to-follower clearance has opened up to 0.01 mm or more — through wear, a loose follower stud, or a follower roller that's lost its needle bearings — there's now slack in the system, and reaction torque from the payload at dwell rotates the turret through that slack.
Quick check: with the machine off and locked out, push the turret tangentially by hand. Any perceptible rotation means the preload is gone. Replace the worn follower or shim the eccentric followers (most quality indexers have one or two adjustable eccentric followers exactly for this re-preload).
Modified sine gives lower peak acceleration but higher peak velocity for the same index time. Modified trapezoid gives lower peak velocity but higher peak acceleration. On a payload-heavy turret — say, a tool changer carrying 25 kg tool holders — pick modified sine because peak inertial torque on the cam shaft scales with acceleration. On a fragile-product line — say, glass ampoules in a nest — pick modified trapezoid because peak product velocity is what slings the ampoules out of their nests.
The trade is roughly 13% higher peak acceleration on mod-trap versus mod-sine for the same index, and roughly 12% lower peak velocity. Pick the one whose downside your line can absorb.
References & Further Reading
- Wikipedia contributors. Cam. Wikipedia
Building or designing a mechanism like this?
Explore the precision-engineered motion control hardware used by mechanical engineers, makers, and product designers.
