The Buchanan rock crusher illustrated by Hiscox uses an eccentric shaft and toggle drive to move its crushing jaw. Rear screws and side rods adjust the outside jaw to set the crushing opening.
The animation calculates a connected eccentric, pitman and two-toggle linkage. Its calculator reports closed, open and current outlet gaps and the eccentric radius needed to produce the entered stroke in this illustrative geometry. An outlet setting alone does not guarantee a particular largest product size.
Buchanan Rock Crusher Interactive Calculator
Inspect a connected eccentric-and-toggle crusher and calculate its outlet openings. The entered stroke determines the required eccentric radius for the stated model geometry.
Equation Used
- Planar rigid links with the specified fixed pivots.
- Crushing face 40 mm ahead of the jaw pivot line.
- Outside jaw fixed during each cycle; linear flare F/800.
- Continuous lower-pitman and left-jaw assembly branches.
- No force, wear, capacity or product-distribution prediction.
Illustrative 800 mm jaw arm and specified toggle geometry. Closed and open settings are horizontal gaps, not guaranteed product sizes. Playback slowed 20 times.
Eccentric rotation drives a connected toggle train
The flywheel turns about a fixed shaft center. An offset journal carries the upper end of the pitman. The lower pitman pin joins a rear toggle connected to the frame and a front toggle connected to the swing jaw.
The swing jaw turns about its upper pivot. Every pitman, toggle and jaw-arm length stays constant through the full shaft revolution. The grey outside jaw is stationary during operation; the setting screw and tie rod indicate its adjustment arrangement.
The outlet is measured horizontally from the outside jaw to the bottom of the moving crushing face. The enlarged outlet view uses that solved distance, making the small working stroke easier to see without exaggerating the motion in the main linkage.
Change the setting and requested stroke
Closed-side setting is the minimum horizontal outlet opening over one cycle. Open-side setting is its maximum. Entering a larger stroke asks the model to solve a larger eccentric radius while maintaining the same rigid-link lengths.
The feed dimension sets the illustrative outside-jaw flare: its horizontal change over the 800 mm jaw height equals the entered feed dimension. This gives the drawing a variable chamber shape; it is not a material-admission or nip-angle test.
Shaft speed changes cycle frequency and playback speed. The animation runs twenty times slower than the entered speed so the eccentric and toggle movement can be inspected. It does not model rock fracture, gravity flow through the chamber or drive torque.
Rigid-link closure and measured outlet travel
The model uses an 800 mm swing-jaw arm, a 700 mm pitman, a rear toggle of √(450²+200²) mm and a front toggle of √(500²+200²) mm. These are stated illustration dimensions, not measured dimensions of a historical machine.
With jaw pivot J=(0,800), shaft center O=(500,500) and rear toggle anchor R=(950,0), the eccentric pin is E=O+e(cosθ,sinθ). The lower pitman pin P is the lower intersection of a 700 mm circle about E and a rear-toggle circle about R. The jaw pin Q is the left intersection of an 800 mm circle about J and a front-toggle circle about P.
The crushing face lies 40 mm ahead of the jaw pivot line. Let B be its lower end, k=F/800 and x0 the outside-jaw position at y=0. The outside-jaw line is x=x0−ky, so the current horizontal gap is Bx+kBy−x0.
The solver finds the minimum and maximum of that gap through a revolution, then adjusts eccentric radius until their difference equals the requested stroke. The outside jaw is positioned so the minimum equals CSS. Thus OSS=CSS+S. Cycle frequency is shaft rpm divided by 60.
A 75 mm closed setting with 30 mm stroke
These inputs give a 75 mm minimum outlet and a 105 mm maximum outlet. The live readout shows the intermediate opening as the connected mechanism rotates.
At 300 rpm, the jaw completes five cycles per second. The inspection animation slows that to one displayed cycle in four seconds.
A nominal 600 mm feed dimension divided by the 75 mm setting gives 8:1. That is labeled as a feed-to-setting dimensional ratio. It is not a measured feed-to-product reduction ratio and does not establish a 100 mm maximum product.
What a setting does not predict
Discharge opening, fragment shape, feed grading, rock behavior and operating conditions all matter to a crusher’s output. This geometry model does not calculate capacity, product grading, motor power, bearing loads or structural strength.
The picture explains the historical eccentric-and-toggle arrangement using the dimensions stated above. It is not a manufacturing drawing. No universal bearing clearance, bolt torque, wear rate or service-life value is inferred from it.
Changing a real crusher’s setting or replacing its linkage parts requires the information for that machine. The calculator’s derived eccentric radius applies only to the geometry stated here.
Buchanan-crusher questions
Does the outlet setting determine the largest product size?
No. The calculator reports opening dimensions. Product size also depends on fragment shape, feed grading, rock behavior and operating conditions.
Does the eccentric radius equal half the jaw stroke?
Not generally. The pitman, toggle angles, jaw pivot and face position transform the eccentric movement. This model solves that relationship.
Why are the toggle plates not changing length?
They are rigid links. Circle intersections enforce their pin-to-pin lengths at every animated position.
Does the outside jaw move during the cycle?
It stays fixed at the chosen adjustment. The eccentric drives the other jaw.
What does changing feed dimension do?
It changes the illustrative chamber flare and the feed-to-setting comparison. It does not simulate a rock entering or breaking in the chamber.
Can these inputs calculate tonnes per hour?
No. The page does not claim a capacity result from these dimensions and shaft speed alone.
Historical mechanism reference
Gardner D. Hiscox, Mechanical Movements, Powers, Devices and Appliances, figure 1234, printed page 304. The drawing and text identify the eccentric, toggle drive, outside-jaw adjustment screws and side rods. The animation uses the illustrative pivot dimensions stated above.
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