A grooved heart-cam is a face cam with a closed heart-shaped groove milled into one side, driving a roller follower through a complete reciprocating stroke for every revolution of the cam. Unlike an open plate cam that needs a return spring, the groove constrains the follower in both directions, so motion stays positive even at high speed. The heart profile delivers near-constant velocity across most of the stroke, which is why textile traverse drives, yarn winders, and certain optical scanning rigs rely on it to lay material evenly without dwell.
Grooved Heart-cam Interactive Calculator
Vary stroke, cam speed, roller size, groove clearance, and constant-velocity fraction to see traverse speed, groove width, and active stroke zone.
Equation Used
The calculator uses the heart-cam relationship that one cam revolution produces one complete out-and-back traverse. For an ideal constant-velocity profile, the follower travels twice the stroke per revolution, so traverse speed is v = 2*S*N/60. Groove width is the roller diameter plus the selected clearance.
- One full out-and-back reciprocating cycle occurs per cam revolution.
- Stroke is completed once per half revolution in the ideal constant-velocity heart-cam model.
- Groove clearance is the total width increase over roller diameter.
- Constant-velocity zone is estimated from the selected fraction of stroke.
Inside the Grooved Heart-cam
The cam is a disc — typically hardened tool steel, 45-58 HRC on the groove flanks — with a closed groove cut into one face. The groove traces a heart shape: two symmetrical lobes meeting at a sharp inside cusp at the top and a smooth turnaround at the bottom. A follower roller sits inside that groove. As the disc rotates, the groove pushes the roller radially outward through one half of the rotation, then pulls it back through the other half. Because the groove constrains the follower on both sides, you get positive motion in both directions without needing a spring loaded against the back of the follower.
The geometry is what makes it useful. The flanks of the heart are cut as Archimedean spirals — radius increases linearly with angle — so the radial velocity of the follower stays constant across most of the stroke. Constant velocity means the yarn, ribbon, or workpiece being traversed gets laid down at uniform pitch. If you used a simple eccentric instead, the follower would slow at the ends of stroke and speed up through the middle, leaving a heavy band of material in the slow zones.
Tolerance on the groove width is the single biggest spec issue. The groove must be 0.02-0.05 mm wider than the roller diameter — not less, or the roller binds on reversal at the cusp; not more, or the follower clatters as the load flips from one flank to the other. We see this fail on retrofit jobs all the time. If you notice a clicking sound timed to once-per-revolution, you have backlash at the cusp and the groove has worn oversize. The fix is regrinding both flanks and fitting a slightly larger roller, not adding a preload spring — that defeats the point of the closed groove.
Key Components
- Cam disc: Hardened steel disc carrying the heart-shaped groove on one face. Typical thickness 12-25 mm with the groove cut 6-10 mm deep. Concentricity of the groove centerline to the bore must hold within 0.01 mm or you get a once-per-rev velocity error.
- Heart-profile groove: Closed track formed by two mirrored Archimedean spirals meeting at an inner cusp and a smooth outer turnaround. The constant-rise spirals deliver uniform follower velocity across roughly 80% of each stroke, with brief acceleration phases near the dead points.
- Roller follower: Hardened ground roller, usually 8-20 mm diameter on a needle bearing, riding inside the groove. Diameter must match the groove width within +0/-0.05 mm. Worn rollers are the most common service item — replace when measured radial play exceeds 0.08 mm.
- Follower carrier or yoke: Slides on a linear rail or guide rod and converts the radial motion of the follower into linear traverse. Carrier mass directly drives the inertial load at the cusp, so we keep this part as light as the strength allows — aluminium where loads permit.
- Drive shaft and bore: Keyed shaft turning the cam disc. The bore must match the shaft within an H7/h6 fit. Any rotational slop here shows up directly as traverse-position jitter on the laid product.
Who Uses the Grooved Heart-cam
Grooved heart-cams show up wherever you need to translate steady rotation into uniform back-and-forth linear motion without a programming controller. They're mechanical, deterministic, and they don't drift. Failure modes are mostly wear-related — groove flank pitting and roller spalling — and you can see them coming if you listen to the machine.
- Textile spinning: Ring-frame and ring-twister traverse drives, including legacy Saco-Lowell and Marzoli ring frames, where the cam moves the ring rail up and down to build the cop.
- Yarn and wire winding: Precision-wound bobbin builders on SSM and Murata winders, laying yarn at uniform pitch across a 150-300 mm package width.
- Cotton combing: Top-comb traverse on Rieter C-series combers, shifting the comb laterally to spread fibre wear across the comb teeth.
- Optical scanning: Constant-velocity scan-mirror drives on older flatbed scanners and microfilm readers, where uniform sweep rate prevents pixel stretch.
- Glass-fibre roving: Traverse modulators on Leistritz and Owens Corning roving winders, distributing roving evenly along the package length.
- Wire enamelling: Lay-down traverse on enamelled-wire take-up reels, common on MAG and Niehoff fine-wire lines, ensuring even build-up without ridges.
The Formula Behind the Grooved Heart-cam
What you actually need to size is the follower velocity and peak acceleration at the cusp, because those two numbers tell you whether the cam will run quietly at your target RPM or hammer itself to death. At the low end of typical operating speeds, follower velocity is gentle and acceleration at the cusp is well within roller-bearing limits. Push toward the high end and cusp acceleration scales with the square of speed — that's where you find the practical ceiling. The sweet spot sits where steady-state velocity meets your process requirement and cusp acceleration stays below roughly 50 m/s² for a standard needle-roller follower.
Variables
| Symbol | Meaning | Unit (SI) | Unit (Imperial) |
|---|---|---|---|
| vf | Mean follower velocity during constant-velocity portion of stroke | m/s | ft/s |
| S | Total stroke length (peak-to-peak follower travel) | m | in |
| N | Cam rotational speed | RPM | RPM |
| acusp | Peak acceleration approaching the cusp (≈ vf2 / rcusp) | m/s² | ft/s² |
| rcusp | Effective radius of the cusp blend arc | m | in |
Worked Example: Grooved Heart-cam in a paper-tube winder traverse
Sizing the grooved heart-cam traverse on a spiral paper-tube winder, modeled on a Paper Converting Machine Company (PCMC) core-winder retrofit producing 76 mm cardboard tubes for textile yarn packaging. The cam moves the glue-application head laterally across a 90 mm stroke. Nominal cam speed is 120 RPM, with a typical operating range of 60-240 RPM. Cusp blend radius is 4 mm.
Given
- S = 0.090 m
- Nnom = 120 RPM
- Nlow = 60 RPM
- Nhigh = 240 RPM
- rcusp = 0.004 m
Solution
Step 1 — at nominal 120 RPM, compute mean follower velocity. The follower covers two strokes per revolution (out and back), so multiply stroke by 2 × revs per second:
Step 2 — estimate peak acceleration at the cusp. The follower reverses direction over the small blend radius at the inner cusp, so peak acceleration is approximately v² / r:
That's around 3.3 g — well within what a 12 mm needle-roller follower handles without complaint. Glue lay-down feels smooth and the carriage tracks cleanly.
Step 3 — at the low end of the operating range, 60 RPM:
At 60 RPM the carriage moves at walking-finger pace. You can watch the glue head crawl across the tube. Cusp acceleration is gentle — the follower whispers through reversals, but throughput is half of nominal.
Step 4 — at the high end, 240 RPM:
That's 13 g at the cusp. In practice you start to hear a sharp tick on each reversal, the follower roller heats up within 20 minutes of run time, and groove-flank pitting shows within a few hundred hours. Above roughly 200 RPM on this geometry, you should switch to a larger cusp blend radius or a modified-sine profile rather than a pure heart-cam.
Result
Nominal mean follower velocity is 0. 36 m/s with cusp acceleration around 32 m/s². At 0.36 m/s the glue head sweeps across a 76 mm tube in roughly a quarter of a second — fast enough for a production line, slow enough that the bead lays flat without splashing. Across the operating range, the low end at 60 RPM gives a comfortable 0.18 m/s and only 8 m/s² at the cusp, while the high end at 240 RPM theoretically hits 0.72 m/s but cusp acceleration jumps to 130 m/s² and the cam starts to self-destruct — the sweet spot sits between 100 and 160 RPM. If you measure follower velocity below predicted, check three things in this order: (1) keyway slop on the cam-to-shaft fit causing lost motion at each reversal, (2) the follower roller diameter undersized relative to the groove, letting the carrier lag the cam by 1-2°, or (3) groove-flank wear at the high-radius portion of the heart, which flattens the spiral and shortens effective stroke.
Grooved Heart-cam vs Alternatives
A grooved heart-cam is one of three common ways to convert rotation into reciprocating linear motion. The other two are a Scotch yoke driven by a crank, and a servo-driven ball screw under software control. Each has a place — the heart-cam wins on simplicity and uniformity, loses on flexibility.
| Property | Grooved Heart-cam | Scotch Yoke | Servo Ball Screw |
|---|---|---|---|
| Velocity profile | Near-constant across ~80% of stroke | Sinusoidal — fast in middle, slow at ends | Programmable, any profile |
| Practical max RPM | 200-300 RPM before cusp wear dominates | 400-600 RPM, smooth acceleration | Limited by ball-screw critical speed, typically 1500-3000 RPM |
| Position accuracy | ±0.05 mm with ground groove | ±0.1 mm typical | ±0.005 mm with encoder feedback |
| Cost (mid-stroke unit) | $200-600 cam plus follower assembly | $80-200 crank and yoke | $1500-4000 with drive and controller |
| Reliability / lifespan | 20,000-40,000 hours before regrind | 30,000+ hours, fewer wear surfaces | 10,000-15,000 hours on screw, drive electronics shorter |
| Reprogrammability | None — profile is fixed in metal | None — geometry fixed | Full software control |
| Best application fit | High-uptime traverse needing uniform lay | Simple reciprocators where profile shape doesn't matter | Variable-product runs needing recipe changes |
Frequently Asked Questions About Grooved Heart-cam
That wear pattern almost always points to follower preload from a misaligned linear guide, not from cam dynamics. If the carrier rail isn't parallel to the cam face within roughly 0.05 mm/m, the follower presses harder against one flank than the other through the long constant-velocity portion. Hertzian contact stress at the high-radius region is already higher than at the cusp because the contact angle is shallower there, and any side load multiplies that.
Quick diagnostic: pull the follower, blue the flanks, and rotate by hand. Uneven blue transfer along the long flanks confirms it. Re-shim the carrier rail before regrinding the groove, otherwise the new surface wears in the same pattern within months.
It's not the kinematics that break — the spirals scale fine — it's the cam diameter. Stroke equals roughly 2 × the radial difference between the inner and outer extremes of the groove, so a 150 mm stroke needs a cam disc north of 400 mm diameter to keep the spiral pitch reasonable. Above that you start fighting cam mass, polar inertia at start-stop, and the cost of grinding a large hardened blank.
For long strokes most builders switch to a barrel cam (cylindrical groove) or a Scotch yoke with a long crank. Heart-cams stay sensible from about 10 mm up to 120-150 mm of stroke.
Always roller in a closed groove. A flat follower needs a single contact surface and an external return spring — that's a plate cam, not a grooved cam. The whole point of the closed groove is positive bidirectional constraint, and only a roller fits inside the groove with proper line contact on both flanks.
Pick the roller diameter to match the groove width within +0/-0.05 mm. Needle-bearing rollers handle the speed range better than plain bushings — bushings overheat at the cusp where sliding velocity peaks.
The cam usually is fine — the click comes from accumulated backlash everywhere except the groove. Check, in order: the keyway between cam disc and drive shaft (loose keys cause a 0.1-0.3 mm rotational lurch at each reversal), the follower-pin to roller-bore fit (worn pins develop radial play), and the carrier-to-rail clearance.
If you tightened all three and the click remains, only then measure the groove width. By that point you're usually 0.02-0.04 mm oversized at the cusp from steady wear, and a regrind is due.
Decide based on whether constant velocity matters more than smooth reversal. A true heart profile gives you genuinely constant follower velocity across most of the stroke — yarn winding, glue laydown, fibre roving all need this because deposition rate is proportional to traverse velocity. The penalty is a sharp acceleration spike at the cusp.
A modified-sine profile rounds the velocity peak slightly and softens the cusp acceleration by 30-40%, at the cost of small velocity ripple in the middle of the stroke. Use modified-sine above about 250 RPM or where stroke is short (under 30 mm) and the cusp dominates the cam life. Stay with true heart below that — the uniform deposition is worth it.
40-50°C above ambient is at the edge of acceptable but tells you something is marginal. The dominant heat source on a grooved heart-cam follower is sliding friction at the cusp where the roller has to reverse direction faster than its rolling velocity allows — at the instant of reversal the roller is briefly skidding rather than rolling.
Check three items: groove lubrication (a light grease film should be visible — dry grooves drive heat fast), roller-bearing condition (a worn needle bearing adds drag and heat together), and operating speed relative to your cusp radius. If you can't change those, increasing the cusp blend radius by 50% during a regrind drops follower temperature noticeably because it cuts the peak skid velocity.
References & Further Reading
- Wikipedia contributors. Cam. Wikipedia
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