I'm using the existing turret. It was originally turned by an air motor, and upon triggering a sensor, an air cylinder shot a catch out into a ratchet wheel type of deal to stop the turret at the right position, at which time another air cylinder clamped it down on to a set of tapered lock pins. Trouble is, that design was endlessly problematic. So I'm using a stepper to rotate it into position, at which time it locks onto the pins via the original air clamping system.  Trouble is, if the stepper didn't get it exactly where it had to be, it rotates slightly upon locking. Which means it starts slighlty out of position for the next tool change. The problem keeps compounding, and after 10 or 20 tool changes, its out of position enough that it can't lock. Why doesn't the stepper always get it there? The steps per degree don't work out to an even number. Stir in a little backlash, and the whole setup fails to be reliable. So, I'd like to use sensors at each position to stop it, rather than rely on the stepper alone, because it really has no way of knowing that it's gotten out of position slightly.

I know this can be implemented via PLC, but I don't know jack about them, or how to utilize modbus to talk to them. I have enough inputs left to just use mach, whether using 8 inputs, or using some sort of switch matrix that could reduce it to four inputs.

Kevin

Hood,

Space is very tight for my turret sensor, so I planned on using small Honeywell halls, in a TO-92 package. They would end up being epoxied into a plastic block, and then the arm/wheel with magnets could just ride over the top. The original 8 position sensor was made this way, and I modified it with one of these honeywell switches to make the turret home sensor I'm using now, which has worked well.

That being said, I'm still kind of unclear on how to arrange the switches and magnets mechanically, to utilize your suggestion about only needing 4 inputs instead of eight.

Thanks again for everyone's replies!

Kevin

I use PLCs with my machines and it makes things like turrets so easy to automate and really they are quite easy to use or at least the Direct Logic ones are, I have written quite a few ladders for toolchanger, 3 for myself, one for a guy in the USA with a 12 pos turret, one for a guy with a toolchanger on his mill and only a few days ago I did one for a friend that is about to put an 8 pos turret on his lathe.
Having said that it can be done with direct inputs/outputs to/from Mach and VB.
For the sensors you would just need differing magnets at each position. If you look at the example I gave earlier
Pos 1 would have 1 magnet to trigger  switch 1,
Pos 2 would have one to trigger switch 2,
Pos 3 would have two to trigger both switches  1 and 2
Etc
Hood

you could still use mach, use a second parallel port with pins 2-9 as inputs and have a common feed to the turret and eight switches (electronic or otherwise). Use the inputs and write the code to look at each position/input, it would be pretty easy code to write.