Alternate Spindle control using Step/Direction

i have a 5i25-7i76 setup and i was wondering if i could use the 5th sted/dir axis on tb3 to control a spindle instead of the 0-10v spindle control on tb4? would there be an issue with index input?

You can use a stepper as a spindle motor, PNCconf will configure it in velocity mode.
It's not well tested.
As far as the index, I'm not sure what you mean.
You would still need a encoder for feedback, the step generator component does not have an index pin available.

Well actually the firmware does but there is no driver support...

The path of least resistance is probably to use an encoder

too bad, that could be quite a selling point - a spindle drive that can tap / index without an encoder...
hmm i guess one would need the 'step' count too

I do think its possible to do this even without an index signal

This has been discussed on the LinuxCNC IRC channel, in the context of using a spindle encoder without a index.

Basically you make a simulated index comp that does a step count mod counts/turn calculation
and simulates the normal encoder index

This would work with an encoder or a (well tuned) step/dir drive

Limitations are that the index position only survives the time the linux CNC session is running
so if you crash and restart, you wont be able to continue a threading session

well i tried it last night just turning my 4 axis into spindle seemed to work well.
the index im talking about is the one that is used for the spindle TB3 pins10-15.
what i'm wanting to do is use a dugong drive with a servo 100v 30amp.
it will fit nicely on the mill.
it has an index available thats not being used by the dugong drive.
now the question is can i just y the encoder leads and feed the 7i76 and the dugong at the same time or will the encoder not supply enough power.
is there something that i can use to output to both devices without interfering with the timing.

You should be able to "Y"the signals
are the encoder signals single ended or differential?

i have to use differential for the drive.
www.cnc4pc.com/Store/osc/product_info.ph...4_78&products_id=337
so i would imagine since it drives 100meters it should have plenty of power to feed both.
if i got time tonight i'll hook it up to my servo on the bench.
got 3phase breaker in for my super nice bridgeport.
i know i know what the hell am im fooling with this little thing for.
well its a test for 2 much larger conversions.

One problem I have noticed is that when you command M05 or (strangely) S0, there is no ramping to zero.
I should explain that pncconf sets the stepgen in velocity mode and sets acceleration and velocity limits.
This is because linuxcnc it's self does not do any ramping of the spindle.

But M05 disables the stepper enable pin and apparently so does S0.
The step gen is designed to stop as quickly as possible - not the best thing with a large chuck....

We need a ramp-to-zero-speed pin for the step gen or linuxcnc needs to plan the spindle ramping - for an elegant solution.

There are surely ways around this by using a bunch of components to monitor enable, and modify commanded speed.
Or if your step drive has an enable pin that lets the motor free wheel that would work too..

Chris M

hmm maybe I should connect the spindle enable pin to machine-is-on signal.
Then the spindle would ramp up and down unless the machine was turned off or estopped.

I think I'll test that....