Full Revolution Clutch
A full revolution clutch is a mechanical clutch used on power presses that, once tripped, cannot be disengaged until the crankshaft has completed one full revolution and the slide has completed a full stroke. Under OSHA 29 CFR 1910.211(d)(5), it is a positive mechanical clutch (pin, dog, collar, or rolling key) between the flywheel and crankshaft, ensuring the press performs one complete machine stroke before stopping.
Full revolution clutches are found primarily on older mechanical power presses in metal forming, fabrication, and general manufacturing. On the shop floor, they are operated via foot treadle or two-hand trip controls, with a single-stroke mechanism required to prevent continuous cycling. Once tripped, the stroke cannot be interrupted, so safeguarding focuses on keeping operators out of the point of operation for the entire cycle using fixed barrier guards, interlocked gates, or two-hand trips at a safe distance. Presence-sensing devices like light curtains are not acceptable as primary safeguards because they cannot stop the motion mid-stroke. Compliance requires proper single-stroke and anti-repeat mechanisms, lockout/tagout procedures, and risk assessments per OSHA 1910.217 and ANSI B11.1/B11.19.
How do I definitively determine if a press has a full-revolution clutch?
Per OSHA, determination is based on physical clutch design: a mechanical pin, dog, collar, or rolling key between flywheel and crankshaft that couples them positively for one full revolution once engaged. Indicators include no air line to the clutch, an operating rod or mechanical linkage from controls, and the inability to disengage the clutch until the crankshaft completes a full revolution and the slide a full stroke.
Why are presence-sensing devices (light curtains) generally not acceptable as primary safeguards on full-revolution presses?
Presence-sensing devices require the control system to stop hazardous motion before the operator reaches the danger zone. On full-revolution presses, once the clutch is tripped, the drive train is positively locked for a full revolution, and the slide must finish its stroke before stopping. The control system cannot disengage the clutch mid-stroke, so light curtains cannot stop motion in time. Fixed barrier guards, interlocked gates, or two-hand trips at safe distance are required.
What are the design and performance requirements for single-stroke mechanisms on full-revolution presses?
Under 1910.217(b)(3), full-revolution clutch machines must incorporate a single-stroke mechanism. If spring-dependent, springs must be compression type, operate on a rod or be guided within a hole or tube, and prevent interleaving of coils on breakage. Functionally, it must ensure one stroke per actuation even if controls are held down, and no continuous cycling. Verification involves observing the press while holding controls to confirm only one stroke occurs.