Tom,
Switches are a non-starter. You will never get the cycle rates you are
looking for. I suggest you keep it simple and stick to hall effect sensors,
amplifier and a solid state switch. Then drive a mechanical solution like an
electrical clutch and brake or a simple dog clutch and latch or if the lever
forces are not so high, a simple electrical solenoid. Avoid optical sensors
in a contaminated environment, because dirt will get you. Hall effect
sensors work in all conditions. Resolve the problem with simple electronics.
I would not use pneumatics, as response times are poor and leaks are a
pain.. If you use a solid state magnetic solution, be wary of back emf
reverse biasing the solid state switch and use a diode of reverse polarity
across the coil.
Steve

"Tom Gardner" wrote in message
...
In this pic, you can see a cam that operates a lever that is part of a
wire cutter. This is an old pic and we now use a roller instead of a cam
but the chain drive is the same. I want to replace this whole drive
mechanism with an air cylinder to move that lever. I roughly figure a 2"
bore x 1" stroke will have enough guts.

http://metalworking.com/Dropbox/_200...ob290-head.JPG

I need the cut timed within one degree of rotation of the same 1" shaft
that drives the chain. I want to be able to easily adjust the timing and
have adjustable dwell. Is there an off-shelf item to do this? I will
need two separate operation switches on the shaft.

I currently use an air limit switch on the other mechanism driven by a cam
that I constructed and we have to replace those switches four times a year
due to failure. Would electrical limit switches and solenoid valves be
more reliable?

We are building the third of these machines. The first two are constantly
scheduled for overtime and weekends. The logs show less than 70% up-time
due to all sorts of little issues that we are addressing on the third
machine. I'd like to target 90%+ up-time, that would fall in line with
what other machines log.

(tempest in a teapot---I'm the largest manufacturer of these items in the
whole WORLD)