Sourcing Stepper Motors & Drivers, Measuring Spind

rexhunt wrote:

Does anyone have suggestions for a source for NEMA-17(I'm pretty sure this is the size of the current motors) and Polulo compatible drivers in Australia?

What is wrong with the current motors?
What do you mean by "Pololu compatible"? I thought that the Pololu devices _were_ drives. Are you meaning drives that take 5V step/dir signals? That seems to be very nearly all of them.

Also what is the recommended setup for measuring the speed of the spindle?

Hard to say without seeing the machine. Do you want to rigid-tap? Thread?

rexhunt wrote:

When I do the mill I would like the option to be able to tap in some capacity however if that's just going to overcomplicate things I'm happy to give it up.
On the lathe I'd like to be able to cut threads.
The headstock is hollow and has a fair bit of space inside it for whatever system I end up going with.x

You don't want to fill the spindle hole up. One of my gripes with my current lathe is that I want a bigger spindle bore. 3" would be nice,

Adding spindle encoders isn't difficult, but you probably have to make something rather than buy something.

I would actually be surprised if the lathe didn't already have a spindle encoder, or at least an index pulse.
www.cnczone.com/forums/benchtop_machines...athe.html#post833934
Seems to show an encoder, though it is geared up from the spindle, which is likely to be a problem if that also provides the index.

The simplest solution is probably to buy an encoder and belt drive it (1:1)
www.ebay.com.au/itm/281099904847
Is jolly cheap.
I have one of those at home, I will hook it up tonight and work out if it is 400 counts per rev or 400 lines per rev (because encoders count 4 x lines).

It has just occurred to me to wonder if it is possible to count encoder pulses with your hardware. You are using a Beagle Board?

rexhunt wrote:

If I were to get something like that, a simple belt drive and something for an index pulse that should be all I need for threadcutting? I wouldn't need any kind of special belt drive either?

I am not sure what you mean by "special belt drive". The encoder needs to run at exactly the same speed and phase as the spindle, so needs a toothed belt, or gearing.
I have made a number of encoders for my lathe, but ended up with a commercial optical encoder running from a gear that I added to the spindle.

Home-made endocer on the spindle of my mill: picasaweb.google.com/lh/photo/C-6jaOfbge...pFm0?feat=directlink
Toothed-disc and reflective sensors on the lathe spindle: picasaweb.google.com/lh/photo/_hlZumHKbs...pFm0?feat=directlink
Hall-effect gear tooth sensors on the head of a mill: picasaweb.google.com/lh/photo/wE4cF0uBYu...pFm0?feat=directlink
Gear-driven resolver on the same mill (I changed my mind picasaweb.google.com/lh/photo/S4Q4BwdLXk...pFm0?feat=directlink
And some encoders I had laser-cut for a special application. picasaweb.google.com/lh/photo/izs9EehSiB...pFm0?feat=directlink

For your application something like the first one is probably best. I would definitely suggest the transmissive (gap) type sensors over the reflective ones.

I hadn't thought of timing issues, I guess I could try putting together some kind of square waver generator and feeding that into an input and seeing if I can get a high enough frequency for maximum

I suspect that without a dedicated encoder module running in the PRU that you will be limited to 1000 hz sampling, so 400 counts per rev limits you to 150rpm. You might have to go for a single pulse per rev system (which has the advantage of being very easy). Then the maximum speed depends on how long you make that pulse.

rexhunt wrote:

Why do you have more than one pickup on the toothed disk?

Quadrature and index, so that the system knows about speed _and_ direction. For rigid tapping on the mill you do need all three channels.

Would it be possible to feed the output of an encoder through some kind of divider when running at higher speeds and straight through at lower speeds?

Even simpler, you can just ignore that fact that you can't get encoder counts at high speed. As long as you always thread at low speed, it should be OK.