yikes
I just realized to rotate a 4 lobed plate one revolution, the motor drive has to rotate 4 times !
it would now also need a 4 to 1 gear train

The way I see it, you would direct couple the lobe plate to the worm screw that you have. This worm screw needs to rotate once to advance the pin tree 1.85mm each time.
You would have the motors contact switch acting on one of the 4 lobs of the Geneva wheel. That way when the switch is triggered the motor simply keeps running until the lobe wheel completes one revolution. The motor will need to complete 4 revs and thus no need for a gear reduction.

Maybe this triggering could all be done outside Mach. For example, another switch could be placed elsewhere on the machine so after the cutoff wheel has done it's part it retracts and trips the switch. I don't know if that's feasable or not without seeing the machine. Just trying to think outside the box.

Russ, thanks a lot. That sounds exactly what,s needed, but i have had trouble finding a Parker OEM 10, if you have a link that will be appreciated.

I actually do like the Geneva plan from Ray, only thing i`m not getting is how to short the contacts breifly ? is that with a timer ?
Would it be possible to do it with a mach3 brain ? can you change a pin from high to low from a brain ?

The other thing with the Geneva thats getting me going, is i should be able to mount 4 cut off discs, driven off a central motor, and rotate them one at a time to do the cut off opp.
4 times the wheel life. those discs are only 0.030" thick.

I was considering going with Kflop for the 8 axis, but you guys have again showed me how knowledgeable you are and will find a solution to any issue.
Thanks again.

A Geneva can be easily controlled by a brain or a macro.  The output only needs to be active long enough to ensure the Geneva motor has turned far enough that the microswitch comes off the cam and closes, and it will power the motor from there, until it again hits the cam, which will stop the motor, leaving the wheel correctly positioned, and locked in that position, and ready to start the next move.  For something that only needs a small number of fixed positions (up to about 16 or so), a Geneva is FAR simpler, and FAR cheaper. than driving it with a stepper or servo.  All you need is a $30 DC gearmotor, and perhaps a relay.  No motor drivers, no software, no complexity whatsoever, and it's dead reliable, and very rugged.

Regards,
Ray L.

Gecko is due to release an indexing stepper drive soon that would work very well .... any day now. You might inquire.

How about today?
http://www.geckodrive.com/gm215-step-motor-motion-controller.html

Sunofagun !
Just talked to Maris  Marcus last week about it. He said "soon", but also said that a year ago.
Thanks Gerry !
I've got 2 on the way.
Russ

"For something that only needs a small number of fixed positions (up to about 16 or so), a Geneva is FAR simpler........"
...could be true, but this is only 1 position. 1 complete revolution.
With the Geneva, you'd need the aforementioned gearmotor including a drive for it, the Geneva mechanism with whatever indexes you might choose (say 4) then a timing belt (or chain) geared 4:1 , mounting and machine work to set it up ........
I'd still prefer the indexing drive and stepper motor directly coupled to the feed worm shaft.
Software is free, VERY small single incremental move to program (infinitely adjustable for acc, dec and speed) just a few wires to hook up.
Would be much simpler imo.
Russ

If it's one position, doing one rev each time, then all you need is a motor and a cam-operated micro-switch....

Regards,
Ray L.

That's more like it.
 If that would be precise enough (repeatable stop pos.) ... good plan.
Would still need a gearmotor though ... but AC would be OK, no need for a DC controller.

Regards

Don't make it more complex than it needs to be.
The Geneva Wheel doesn't need any more than 4 positions because the important point is that the worm screw must rotate once and park in an accurate, repeatable position. That's why I suggested the wheel.
If you hook it up as I suggested in my reply #10 you don't need a reduction drive of any sort.
If you use a DC motor, relay and micro switches to drive the wheel then you don't need software, programing or driver boards etc, you simply use a DC supply feed that I assume can be got from the computers supply rail.
Simply using a cam operated switch mounted on a gear motor won't give you a repeatable stopping position as the motor will always over run to some extent once the switch is tripped. The Geneva Wheel addresses this situation.
I guess I'm looking at the original post, which talks about all 6 axis ports being used in Mach3, so the 7th axis would need to be controlled mechanically.

Hi ozy,
  As I see your example, the Geneva would need to index through 3 full cycles, then stop on the fourth (without 4:1 gearing) to make 1 full revolution.
Quite time consuming just to make 1 rev at the feed screw.
But would certainly work as you describe.
Am I seeing your example right ?
Thanks,
Russ

Hi ozy,
  As I see your example, the Geneva would need to index through 3 full cycles, then stop on the fourth (without 4:1 gearing) to make 1 full revolution.
Quite time consuming just to make 1 rev at the feed screw.
But would certainly work as you describe.
Am I seeing your example right ?
Thanks,
Russ

Yeah, that's how I see it.
The speed of the Geneva Wheel is soley governed by the choice of the actuating motor. They can run at a very high speed if made accuratly and with bearings etc.
To eliminate the time factor, the wheel could be advancing whilst a cut off wheel or welder was retracting for example.

I remember as a kid, my Dad gave me a people counter from an old showground that was being pulled down. The counter consisted of several Geneva Wheels in a row to change the numbers of people through the gates. I used to hook the counter up to an electric drill to see how fast I could make the numbers incresase. Believe me when I say that they can operate at quite high speeds and survive. 
It was my knoledge of this counter that made me suggest it in the first place.