Spindle Control through EMC2

Peter_Cassar wrote:

I believe that EMC2 can output a PWM signal to control spindle speed. What about direction?

There are spindle-cw and spindle-ccw pins that can be directed to output pins (parallel port or DIO card).

And what about step and direction control as supported in TurboCNC? I'd like to know if EMC2 can do step and direction for spindle speed control

Yes, no problem. You would connect the spindle speed to a velocity-mode stepgen component in HAL and then take the output pins of that to physical output pins.
HAL is the EMC "HArdware Abstraction Layer" which allows you to connect all the inputs and outputs of the various parts of EMC together in almost any way you choose, optionally through intemediate processing and logic blocks. This is all done in a configuration file, and lines like
net spindle-cmd motion.spindle-speed-out => stepgen.4.velocity-cmd
means that the current spindle speed demand is passed to a step generation function. (which in turn has output pins that are linked to physical IO using similar lines).
For most configurations this file can be created by the stepconf (or pncconf) wizard. For a step-dir spindle you would need to hand-edit as it is a non-typical configuration.
You can do almost anything in HAL, and when you find something you can't do then it is surprisingly easy to create a custom HAL component that does do what you want. Most things already exist though, there is a full list of them beginning half way down this page:
www.linuxcnc.org/docview/html/

Also on the subject of spindle encoders. I have read in places that EMC2 can use a simple 1 pulser per revolution signal. I've also read that it can accept quadrature encoded signals. Which is better?

You need one pulse per rev anyway for spindle index. Quadrature adds finer resolution and better feedback, which is good for spindle-coordinated motion like rigid tapping, lathe threading or even elaborate things like cam-turning:

I would appreciate some advice on these questions as I'm in the process of deciding on harwdware for a lathe conversion. .

You might want to think about making your own spindle encoder. The problem being that lathes have large through-bores and encoders typically don't.
Otherwise plan to run the encoder from a toothed belt on the spindle.
If there is a handy gear fixed to the spindle then a pair of proximity sensors an integer number of pitches + 0.5 apart will give you the quadrature signal, and the index can be from any convenient feature.
If the lathe is fairly heavy, such that spindle speed varies little during a threading pass then you can start with just a 1ppr encoder and see how it goes.
The first encoder I had was made with a laser printer, stripes and an index wrapped round the spindle tube. It actually worked fairly well, but started to peel off and was replaced by an aluminium disc on the drive pulley with slitting-saw slots in it.
A Parallel port has enough pins for a stepper-based lathe, and you probably won't run out of speed with software step generation on the axes. You might find that you run out of step rate with a step-direction spindle drive though. You also need to look carefully at the spindle encoder resolution and the base thread rate of your PC if you are going to use software encoder counters.

There is a wide range of external/internal hardware that can be used for step / pwm / encoder / motor driving etc. If you are thinking along those lines than perhaps start a new thread asking for advice. All I will say at this point is that a Mesa 7i43 is $80 and converts your P-Port into a 48 channel IO device with enormously faster PWM, stepgen and encoder counters. Other hardware and suppliers exist, though and might have hardware better suited to your needs.

Peter_Cassar wrote:

I'm wondering now if 100CPR is adequate to achieve enough resolution.

The video is done with a 100-slot (400 edge-count) encoder ring.
If you run a 20uS base thread and a software encoder counter following a 400 count encoder you start to run into problems at 3000rpm or so. But then you are rather unlikely to be doing coordinated moves at 3000rpm.