An eight-stamp ore mill crushes material beneath heavy guided stamps. Cams on a common powered shaft lift tappet collars on the stamp stems, then let the shoes fall onto ore above fixed dies.
The animation separates cam-driven lift from gravity-driven fall. Its calculator reports ideal drop energy, drop frequency, fall time and average lifting power. The number of active stamps and the number of cam lobes per revolution are separate inputs.
Eight-Stamp Ore Mill Interactive Calculator
Inspect the cam lift and free fall of up to eight stamps. Calculate ideal drop energy and lifting power with an explicit choice of one or two drops per shaft revolution.
Equation Used
- Rigid vertical guides and fixed dies.
- Illustrative 120-degree half-cosine lift cam.
- One or two lobes with evenly staggered releases.
- Gravity 32.174 ft/s²; zero vertical release velocity.
- No rebound, friction or material drag; not a motor-sizing result.
Weight is pounds-force; height converted from inches to feet. Zero vertical release velocity, gravity-only fall and no rebound. Ideal power excludes drive losses.
The cam lifts; gravity supplies the drop
Each shoe, stem and tappet collar moves as one vertical assembly. Fixed guides keep the stem aligned. A wiping cam raises the underside of the collar. When its working edge moves clear, the stamp is no longer constrained by the cam and falls toward the die.
The front view shows the eight-station frame, common shaft, belt drive, stems, shoes and two mortar compartments. The enlarged end view makes cam contact and release visible. A colored point identifies contact during lift; it disappears during free fall.
Release events are evenly staggered among the active stations in this model. One lobe gives one drop per stamp per shaft revolution; two opposite lobes give two. The historical illustration does not specify the exact phasing or measured cam profile used here.
Inspect the lift-and-drop cycle
Use release height to change the shoe travel and fall time. Weight changes energy and ideal lifting power, while gravity-only fall time is independent of weight. Shaft speed changes how often the cams lift the stamps.
The animation runs at one quarter of the calculated speed so the release and fall can be inspected. You can pause it or scrub the shaft angle. Reducing the active count leaves the other stations empty rather than drawing eight moving stamps with a smaller count in the calculation.
Hiscox’s figure 1236 shows a belt-driven eight-stamp arrangement with successive cam lifts. The braced frame and mortar layout follow that form. The displayed pulley ratio, structural dimensions and cam profile are illustrative choices.
Energy, frequency and ideal power
Let W be the moving assembly’s weight in pounds-force, h its release height in feet, N shaft rpm, n active stamps and k drops per stamp per revolution.
E=Wh; drops/min=nNk; ideal hp=WhnNk/33000
Height entered in inches is divided by 12. For release from zero vertical velocity, free-fall time is √(2h/g) and impact speed is √(2gh), using g=32.174 ft/s².
The illustrative cam raises the stamp with s=h[1−cos(πφ/β)]/2 over β=120 degrees. It reaches zero lift velocity at release. After release, s=max[0,h−gt²/2], where t is elapsed physical time. The remaining angle before the next lobe leaves sufficient fall time throughout the slider range.
For the enlarged flat-tappet construction, the contact point relative to the cam center is (ds/dφ,R+s), with R=0.5h. Rotating that point backward by φ generates the working cam profile. The end of the lobe moves outside the tappet’s left edge at release, so the stamp falls independently.
Eight 1000 lbf stamps falling 9 inches
A 9-inch drop is 0.75 ft. Each stamp therefore supplies 750 ft·lbf of ideal gravitational energy per drop. At 40 shaft rpm with one lobe per stamp, eight active stamps make 320 total drops per minute, requiring 7.27 hp of ideal average lifting power.
Each individual stamp drops 40 times per minute in that example. Choosing two lobes increases the total to 640 drops per minute and the ideal average power to 14.55 hp, while energy per drop stays at 750 ft·lbf.
The gravity-only fall time is about 0.216 s and impact speed about 6.95 ft/s. These values describe the ideal free fall, not the impact force or a guaranteed ore-processing rate.
What this calculation cannot size
Ideal average lift power excludes friction, belt losses, drive acceleration, mechanical wear and impact losses. It is not a motor nameplate recommendation or a prediction of peak shaft torque.
Throughput and product size depend on the ore, feed, mortar, screening and operating conditions. They cannot be obtained from drop energy alone. The page does not assign universal service lives, structural tolerances, water rates or production figures to this historical mechanism.
The rigid model assumes no rebound after impact and no additional drag during the fall. Its smooth cam profile illustrates the lifting motion; it is not a manufacturing drawing of a surviving mill cam.
Stamp-mill questions
Why are there two different drop-rate outputs?
One is the rate for a single stamp; the other totals all active stations. Total drops per minute equal individual drop rate multiplied by the active count.
Does every cam revolution give one drop?
That depends on lobe count. This model lets you select one or two working lobes per revolution.
Why does increasing stamp weight not shorten the fall?
Under the gravity-only assumption, all weights have the same gravitational acceleration. Weight increases energy, not the fall time from a given height.
Does the cam force the stamp downward?
No. The cam lifts and releases the tappet. The stamp falls under gravity while the cam remains clear of it.
Does ideal horsepower select the motor?
No. It is the average rate of gravitational potential-energy input and excludes drive losses and peak demands.
Is the visible drop order historical?
The model spaces release events evenly. The historical illustration does not specify an exact drop order.
Historical reference
Gardner D. Hiscox, Mechanical Movements, Powers, Devices and Appliances, figure 1236, printed page 305. The engraving shows the eight-stamp frame and belt-driven camshaft; the description identifies successive cam lifts. The cam profile and mathematical assumptions are stated above.
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