An Internal Multiple Cam is a single rotating drum or disc carrying two or more cam grooves cut on its inside surface, each driving a separate follower along its own motion law. It solves the problem of synchronising several timed motions from one input shaft without a chain of external cams or geared cam stations. Each follower rides its own internal groove, so lift, dwell, and return phases stay locked to the same rotation. You see it in indexing tables, packaging machines, and textile dobbies where 3 to 8 timed motions must agree to within a fraction of a degree.
Internal Multiple Cam Interactive Calculator
Vary roller size, groove clearance, cam speed, and phase error to see groove fit, depth, and timing lag in an animated internal cam diagram.
Equation Used
The calculator follows the article guidance that the roller OD must match the internal groove width within +0.02 / -0.00 mm and that groove depth is usually 1.5 times roller diameter. It also converts cam phase error into time lag at shaft speed, showing why even a small angular shift matters in a phase-locked multiple cam.
- Groove width is roller diameter plus diametral running clearance.
- Recommended groove depth is 1.5 times roller diameter.
- Phase lag converts angular clocking error into time at the selected shaft speed.
- Article fit guidance treats 0.02 mm clearance as the practical upper limit.
Operating Principle of the Internal Multiple Cam
Picture a hollow steel drum, maybe 200 mm diameter, with two or three closed grooves machined into its inside wall. Each groove is a different cam profile — one might lift a pusher, another might rock a clamp, a third might trigger a knife. A roller follower rides each groove, and because every groove shares the same shaft, every motion is phase-locked to the same rotation. That is the whole idea of an Internal Multiple Cam: one input, many outputs, all timed against each other to a fraction of a degree.
The internal groove geometry matters because it constrains the follower in both directions. An external cam needs a return spring or a conjugate cam to pull the follower back; an internal groove pushes and pulls the roller through the full cycle. That is why you see internal cam grooves on high-speed indexing cam drums where spring return would float at 600 RPM. The pressure angle on each groove must stay below roughly 30° at peak velocity — push past that and the roller skids, the groove walls gall, and you get the classic chatter mark every cam grinder has seen.
Get the tolerances wrong and the machine tells you immediately. Groove width must match roller diameter to within +0.02 / -0.00 mm — any looser and the follower rattles between the walls during velocity reversal, any tighter and the roller binds when the drum heats up and the bore expands. Phase shift between the stacked grooves is the other killer. If groove A and groove B are clocked 0.5° off the design timing, a clamp can close before the part is fully indexed, and you get crushed product or a snapped follower arm. Most failures we see come from one of three causes: worn follower bearings letting the roller wobble in the groove, hardened groove walls spalling at the dwell-to-rise transition, or the drive key working loose so the whole drum drifts in phase.
Key Components
- Cam Drum or Disc: The single rotating body carrying all internal grooves. Typically 4140 or 8620 steel, case-hardened to HRC 58-62 in the groove walls. Concentricity between grooves and the bore must hold within 0.01 mm TIR or follower loading goes uneven.
- Internal Cam Groove: A closed-loop track machined into the inside wall, cut to a specific motion law — modified sine, modified trapezoid, or cycloidal. Groove depth is usually 1.5× roller diameter so the follower cannot lift out under shock load.
- Roller Follower: A precision needle-bearing roller, typically 12-25 mm OD, that rides the groove. The OD must match groove width to within +0.02 / -0.00 mm. Anything looser and you get reversal clatter at the velocity zero-crossings.
- Follower Arm or Slide: Translates roller motion into the actual machine output — a lift, a swing, or a linear stroke. Stiffness matters: any compliance here shows up as timing lag and ruins the phase relationship between the stacked motions.
- Drive Shaft and Key: Locks the cam drum to the input shaft. A loose key is the single most common phase-drift failure mode. Use a tight-tolerance key with Loctite 648 on the keyway, or step up to a shrink-disc coupling on machines above 300 RPM.
Where the Internal Multiple Cam Is Used
Internal Multiple Cams show up wherever a designer needs several timed motions from one shaft and cannot afford the backlash of geared cam stations. The advantage is mechanical — once the grooves are cut, the timing relationship is fixed in steel and will not drift over millions of cycles. You find them in packaging, textile machinery, automatic assembly, and any rotary indexing job where multi-track cam coordination is the whole point of the machine. When a single internal cam drum replaces three external cam shafts and a timing belt, you cut part count, you cut backlash, and you cut the noise floor of the machine by a measurable margin.
- Pharmaceutical Packaging: The IMA Adapta capsule filler uses a stacked internal cam drum to drive dosator lift, dosator rotation, and the powder-bed tamping motion from a single shaft, holding 0.1° timing across 200 cycles per minute.
- Textile Weaving: Stäubli dobby heads on Picanol OmniPlus looms use internal multi-track cams to drive heald-frame lift sequences, each track cut to a different weave pattern and selected on the fly.
- Automatic Assembly: Hirata pallet-transfer indexers use an internal double-cam to coordinate pallet lift and pallet clamp from one motor, eliminating the cross-axis cam belt that fails on traditional designs.
- Glass Container Manufacturing: Emhart Glass IS-machine timing drums are essentially large-diameter internal multi-track cams, driving plunger, baffle, and blow-head motions on each section to within 1 ms over a 12 s cycle.
- Cigarette and Tobacco Machinery: Hauni Protos-M5 makers use internal cam drums to time the tipping-paper feed, glue application, and seam roller against the rod-forming garniture at 16,000 cigarettes per minute.
- Can Making: Stolle bodymaker tooling rams are paced by an internal multi-cam that coordinates redraw, ironing, and dome-forming strokes across a single crank rotation at 400 cans per minute.
The Formula Behind the Internal Multiple Cam
The single most useful number on an Internal Multiple Cam is the maximum follower velocity, because it sets the pressure angle, the contact stress, and ultimately whether the groove walls survive. The classic form for a modified-sine motion law gives peak velocity as a function of total lift, cam rotation angle for the rise, and shaft speed. At the low end of typical operating speeds — say 30 RPM on a slow indexer — peak velocity is gentle and pressure angle stays well under 20°, so you can run cheap roller bearings and a softer groove. At the high end — 400-600 RPM on a packaging cam drum — peak velocity climbs into the range where pressure angle approaches the 30° limit, groove walls need full case-hardening, and the follower bearing must be a precision needle type. The sweet spot for most industrial Internal Multiple Cams sits between 60 and 200 RPM, where the geometry is forgiving and the machine still earns its keep on throughput.
Variables
| Symbol | Meaning | Unit (SI) | Unit (Imperial) |
|---|---|---|---|
| vmax | Peak follower velocity during the rise phase | m/s | in/s |
| h | Total follower lift (rise stroke) | m | in |
| N | Cam shaft rotational speed | RPM | RPM |
| β | Cam rotation angle for the rise phase | rad | rad |
| Cv | Velocity coefficient of the motion law (1.76 for modified sine, 2.00 for cycloidal, 2.00 for modified trapezoid) | dimensionless | dimensionless |
Worked Example: Internal Multiple Cam in a chocolate praline depositor
Your team is sizing the internal double-cam drum on a Sollich Turbotemper-linked praline depositor that runs at a contract confectioner in Brussels. The drum drives two stacked grooves — one lifts the nozzle bar 25 mm to clear the shell mould, the second rocks the wiper blade 18° to cut the chocolate tail. The rise phase for the nozzle lift is set at β = 90° (1.571 rad) of cam rotation, and the line is meant to run at a nominal 120 strokes per minute, with a typical operating range from 60 to 200 RPM depending on praline size. You are using a modified-sine motion law (Cv = 1.76) and you need to know peak follower velocity so you can size the roller bearing and check pressure angle at all three operating points.
Given
- h = 0.025 m
- β = 1.571 rad
- Nnom = 120 RPM
- Nlow = 60 RPM
- Nhigh = 200 RPM
- Cv = 1.76 dimensionless
Solution
Step 1 — compute peak follower velocity at the nominal 120 RPM operating point using the modified-sine motion law:
At 0.352 m/s the nozzle bar lifts cleanly, and pressure angle on the groove sits around 22° — well inside the 30° hard limit. This is the sweet spot the machine was designed around.
Step 2 — at the low end of the typical range, 60 RPM, halve the speed:
At 0.176 m/s the cam is loafing. Pressure angle drops to roughly 12°, follower bearing load is low, and the only real concern is that at this speed the chocolate viscosity may matter more than the cam dynamics — the line throughput is the bottleneck, not the cam.
Step 3 — at the high end, 200 RPM, scale up:
At 0.587 m/s pressure angle climbs toward 28°, follower contact stress roughly triples versus the low-end case, and groove wall hardness becomes critical. Above 200 RPM you start hearing the cam — a faint clack at the dwell-to-rise transition is the first warning that the pressure angle is eating into the safety margin.
Result
Nominal peak follower velocity is 0. 352 m/s at 120 RPM, which puts the cam comfortably in its design window with pressure angle near 22°. At the 60 RPM low end the velocity drops to 0.176 m/s and the cam is loafing; at the 200 RPM high end velocity climbs to 0.587 m/s and you are working the groove walls hard — the sweet spot for this drum sits at 100-140 RPM where you get throughput without chasing pressure-angle limits. If your measured velocity comes in 15-20% below predicted, check three things in order: (1) the drive key on the cam shaft has loosened and the drum is slipping in phase against the input, (2) the follower arm pivot bushing has worn 0.1 mm or more and is absorbing motion as compliance, or (3) the groove walls have spalled at the rise transition, letting the roller skip across a damaged section instead of tracking the profile.
Choosing the Internal Multiple Cam: Pros and Cons
An Internal Multiple Cam is not the only way to coordinate several timed motions from one shaft. You can stack external cams on a line shaft, you can use a servo-driven electronic cam, or you can stick with a Geneva indexer if you only need step-and-dwell. Each option has a different cost, speed ceiling, and accuracy footprint. Here is how they compare on the dimensions that actually matter when you are choosing.
| Property | Internal Multiple Cam | Stacked External Cams | Servo Electronic Cam |
|---|---|---|---|
| Maximum cycle speed (typical) | 600 RPM | 300 RPM | 1200 RPM |
| Phase accuracy between motions | ±0.05° | ±0.2° (gear backlash) | ±0.01° (encoder limit) |
| Initial cost (3-axis system) | Medium — single ground drum | Low — off-the-shelf cams + shaft | High — 3 servos + drives + controller |
| Reprogramming flexibility | None — geometry is in steel | None — geometry is in steel | Full — change profile in software |
| Service life before regrind | 50-100 million cycles | 20-50 million cycles | Servo life ~30,000 hr, profile unlimited |
| Load capacity at follower | High — groove constrains both directions | Medium — return spring limits | Limited by servo torque rating |
| Best application fit | High-speed packaging, fixed-cycle assembly | Low-cost, low-speed indexing | Variable-recipe lines, R&D machines |
Frequently Asked Questions About Internal Multiple Cam
Mount a dial indicator on each follower output and rotate the drum slowly by hand. Mark the input shaft at the angle where follower A hits its rise start, then continue rotating until follower B hits its rise start and read the angle difference. Compare this to the timing diagram on the cam drawing.
If the measured offset differs from drawing by more than 0.2°, the drive key is the prime suspect — it works loose under reversing torque even when the screws look tight. Pull the drum, inspect the keyway for fretting marks, and re-fit with Loctite 648 or upgrade to a shrink-disc coupling if the machine runs above 300 RPM.
Internal grooves load the roller in both directions across every cycle — there is no spring-loaded one-way contact like an external cam. The follower bearing sees a complete load reversal twice per revolution, and that reversal cycle is what destroys needle bearings.
If the original spec called for a standard cam-follower bearing, swap it for a full-complement needle type rated for reversing loads (McGill CCYR or INA NUTR series). You will typically see 3-4× longer life with no other changes.
Three questions. First, will you ever change product format? If yes, servo wins because you change the cam profile in software in 10 minutes instead of regrinding steel. Second, what is your top speed? Above 800 RPM mechanical cams are unbeatable for stiffness and repeatability — servos start losing phase accuracy as they fight inertia. Third, what is your maintenance culture? Servos need a controls engineer when they fail; a cam drum needs a millwright. Pick the one that matches the skills you already have on shift.
Almost certainly a step in the groove wall at a tool-path transition. Internal cam grooves machined on a 4-axis need a single continuous tool path with no retract-and-re-engage moves, or you leave a 0.01-0.02 mm step where the tool re-entered. The roller hits that step at one specific cam angle every cycle.
Diagnostic check: rotate the drum slowly by hand with the follower loaded, and feel for the bind angle. Mark it, then sweep the groove at that angle with a fine-grit hone (Sunnen MBB-1660 or equivalent) for 30 seconds. If the bind disappears, you confirmed the tool-path step. The proper fix is to re-machine the groove with a continuous helical tool path.
Thermal growth of the drum is closing the running clearance between roller and groove wall. A 200 mm steel drum heated 20°C grows about 0.05 mm in diameter — if your roller-to-groove clearance was already on the tight side of the +0.02 / -0.00 mm spec, hot running puts you into interference.
Two fixes. Either increase nominal groove width by 0.01-0.02 mm to give thermal room, or improve heat extraction — many high-speed cam drums run with an oil-mist lubrication system specifically to pull heat out of the groove wall. If you are running dry, that is your real problem.
You lose acceleration discontinuity at the dwell boundaries. Simple harmonic motion has finite acceleration at the start and end of the rise, which means a sudden jerk every cycle. At low speeds (under 100 RPM) you may not feel it. Above that, the jerk excites resonance in the follower arm and you get vibration that shows up as marks on the product, fastener loosening, and bearing fatigue.
If you must accept simple harmonic to save money, derate the maximum cycle speed by roughly 40% versus the modified-sine design point. That keeps the jerk-induced loads inside what the rest of the machine can absorb.
References & Further Reading
- Wikipedia contributors. Cam. Wikipedia
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