Whitworth Quick Return Mechanism Demonstration Model

In a shaper or slotter, the tool must cut slowly on the working stroke and race back on the return stroke — idle time saved is production gained. The Whitworth crank-and-slotted-lever mechanism achieves this with a single rotating crank: a pin on the crank wheel slides in the slot of a long pivoted lever, and because the crank's rotation is split unequally between the two extreme positions of the lever, the ram it drives spends more time cutting than returning. In theory of machines classes this is usually a diagram and a timing-ratio formula, and most students never feel the asymmetry they are asked to compute. This project builds a bench-top demonstration model of the mechanism: a hand-cranked (optionally motor-driven) crank wheel, slotted lever, connecting link and guided ram on a fabricated steel frame. Turning the crank makes the timing difference visible and measurable — the student times both strokes, computes the cutting-to-return ratio, and compares it with the geometric prediction.

1. The student turns the hand crank (or runs the optional DC gear motor) at a steady pace, rotating the crank wheel at approximately constant angular velocity.
2. A pin fixed at about 60 mm radius on the wheel slides in the slot of the slotted lever, converting uniform rotation into oscillating lever motion about the lever's fixed pivot below.
3. The lever's extreme positions occur where the crank pin is tangent to the swing geometry — the crank sweeps a larger angle during the working stroke than during the return stroke, which is the source of the quick-return effect.
4. The top of the slotted lever drives the connecting link, which pushes and pulls the ram block along the guide rails: a slow forward cutting stroke followed by a quicker return.
5. The student times one full cycle with a stopwatch — the working stroke lasts about 1.7 times as long as the return stroke, the design target from the nominal geometry (crank radius 60 mm, crank-centre distance approx. 150 mm).
6. Measured times are entered in the timing sheet and compared with the geometric prediction; the student repeats at different crank speeds to show the ratio is a property of the geometry, not of speed.

Tech stack:

• Mild steel flats & angles (fabricated frame)
• Steel crank wheel with crank pin
• Slotted lever & connecting link (mild steel)
• Ram block with twin guide rails
• 608 ball bearings (crank shaft)
• Hand-crank handle (motor-ready)
• 12 V DC gear motor, approx. 30 RPM (optional drive)
• Masking-tape labels, M6/M8 fasteners

• [True Whitworth geometry] A crank pin sliding in the slotted lever produces the genuine quick-return asymmetry from the mechanism's geometry — the same principle the report derives, so the demonstration and the theory agree.
• [Visible cutting vs return timing] The ram's slow working stroke and quick return are plain to see; with a stopwatch the student times both and computes the cutting-to-return ratio against the design target of approximately 1.7:1.
• [Hand crank drive, motor-ready] A hand-crank handle on the crank wheel gives direct control for demonstrations and stroke timing; an optional 12 V DC gear motor (approx. 30 RPM) can be fitted for continuous running.
• [Guided ram and connecting link] The ram block runs between two parallel guide rails, driven by the connecting link from the slotted lever — showing how uniform rotary input becomes straight-line reciprocating output.
• [Bearing-mounted crank] 608 ball bearings on the crank shaft keep rotation smooth and low-friction, so the timing asymmetry is not masked by jerky motion.
• [Labeled demonstration stations] Handwritten masking-tape labels mark the crank wheel, slotted lever, connecting link, ram and guide rails for clear viva and classroom demonstration.
• [Timing observation sheet] A student-run test sheet with columns for crank speed, cutting-stroke time, return-stroke time and computed ratio, so the demonstration yields the student's own results.

• Fabricated Whitworth mechanism model (frame, crank wheel, slotted lever, connecting link, ram, guide rails)
• Hand-crank handle fitted; mounting provision for the optional DC gear motor
• Handwritten masking-tape labels on all key stations
• Stroke-timing observation sheet with a worked example
• Project report PDF (Whitworth geometry, derivation of the timing ratio, build procedure, test results)
• PPT presentation for final review
• Viva Q&A preparation document (quick-return theory, timing-ratio derivation, shaper/slotter applications)

• This is a demonstration model, not a working shaper — there is no cutting tool or workpiece; it demonstrates the drive timing, not metal cutting.
• The approx. 1.7:1 timing ratio is a design target from the nominal geometry; the student's measured values depend on their own timing and on build tolerances of about ±2–3 mm on link dimensions.
• Hand-cranked speed varies between operators, so the ratio — not the absolute stroke times — is the repeatable result; the report states this explicitly.
• Slot-to-pin clearance of about 0.5–1 mm in the built model introduces a small amount of play; the lever dwell this causes is discussed in the report rather than hidden.
• The bolted mild-steel assembly weighs about 8–10 kg (design target) and must sit on a stable bench during demonstration.
• The optional motor drive runs at a fixed approx. 30 RPM; no speed control is included unless ordered.