I have an air cylinder, 1.5" x 4" stroke, that pushes a crank on a shaft to rotate the shaft about 90 deg. On the shaft is a gear with a one-way clutch. The 4" x 1/2" gear turns about 3" at the perimeter per stroke of the cylinder. By moving the link to the air cylinder up or down on the crank the gear will rotate more or less per stroke. A second gear is meshed into the first gear with pressure from another air cylinder. Wire is fed between the gears in a grove cut in the face of each gear. The idea is to feed wire 3" per stroke.
Is works perfectly and fast! By varying the pressure in the cylinder that presses the gears together, the wire is gripped very well at 60 lbs air pressure and will slip through the gears easily at no pressure.
The only problem I have is that the gears over-run and feed too much wire. I've considered lightening the gears by drilling a bunch of holes. Also, a drag brake on one or both gears with screws pressing brass pucks against it. Another idea is an air limit switch that is struck at the end of the stroke by the crank. This switch would unload the pressure on the clamping cylinder and let the wire slip between the gears when they over-run.
Would the air limit switch work fast enough to unclamp the wire in time? Would I be better off with an electric switch and valve? I might have to lighten the gears, brake them and switch off the air clamp The feed has to take place in