What are the pulley settings for, and how are they used?  Do they do more than scale the RPM DRO?  How do you tell Mach which pulley is engaged?

Regards,
Ray L.

Think there is info in tthe manual, I remember reading something a few years back, if its not in there then it could be the customisation manual or the wiki.
Hood

Basically yes.

Your electric motor has a limited span in terms of power and speed. With an inverter running a three phase motor (AC) the motors are designed to be at a constant speed (dependent on the cycles per sec of the power supply (50 in UK 60 in USA). To "fool" it and alter the speed the inverter alters the cycle per sec output. This alters the speed, but also alters the available torque from the motor. This can mean when doing a "big" job on the lathe say something 7" in diameter (alright - not that big) my speed has to come down to between 70 and 200 rpm - depending on the tool. My motor turns the spindle between 0 and 1300 rpm, and down at 200 has hardly any power behind it (despite being twive as large as my original).

You then have to introduce gearing down to get the motor spinning faster - i.e. more power - whilst the job is still turning at the optimum cutting speed. The same applies in reverse - 1300 rpm is not really fast enough for some of the milling jobs I would like to do, so I really should gear it up.

Your gearing table should, therefore have the optimum speeds for that gear set in. They will probably have to overlap to give the best results (or should I say "even" results over a wide range) - my old pulley arrangement had a choice of six "settings" so something similar plus an inverter will give a good range.

You can set the pully directly on the lathe pages, or on the mill pages it is on the settings page.
If you select a speed using GCode using the S command, Mach checks if it can give that speed on the pully shown as selected - and will give a warning if not. There is no code to change the pulley on GCode - since it is a physical action to change the gearing.
Mach quite clearly needs to know what pulley you are on (or which gear you are in) so it can alter the speed of the motor correctly to give the speed requested.

You could, I would imagine, be able to alter the Vis Basic on the S command to check the pulley selected first, and warn you if it could not comply, and stop the machine to allow you to change the gearing. If you were using a CAM program that also selects cutting speeds etc for you, then this would ensure that you were always on top of the job, not just a slave to the machine.

So what exactly does Mach do when it determines you're on the wrong pulley?  And how do I tell what pulley I've changed to?

I've made a custom post for my CAM program (SheetCAM) that takes to tool RPM specified for each operation, and determines what the correct pulley and VFD frequency is, inserts an M00 prompting me to move the belt it necessary, and feed the VFD frequency to the S commands in the G-code (I've scaled the spindle speed response so this works correctly).  It also minimizes pulley changes, by retaining the previous setting if possible.

I"m trying to figure out if there's a better way of doing this.

Regards,
Ray L.

Not sure how Mach does it Ray as I have never had pulleys on my machines. What I can tell you though is about my lathe, it has 16 speeds of which eight are in the headstocks high range and the other 8 in the low range. The speeds within a range can be changed by Mach but to go between the ranges requires changing manually with a lever. What I have is two switches that tell Mach which way the lever is and in my code I have a M91 or M92 (Thats what the old control used) If I call a speed such as M92 S6 (6 equates to 1000RPM in high) if its in high gear the signal is seen by Mach and all is ok, if its in low range then Mach stops and gives me a warning.
 I would think from Jims explanation above Mach is doing similar except its not looking at switches but rather seeing if the speed called can be set from the min and max of that pulley. Now how does Mach know what range you are in? well I suspect the first time you call a speed after starting Mach it will pop up a warning for you to check, if its fine you say so and off you go, from then on in its automic whether you get a warning or not, this would obviously happen every start of Mach.
 Now after all this typing someone will come and tell me thats not the way it works but at least its kept me occupied for a few mins while waiting on the next batch of pieces to weld are being milled

Hood

The new Mach3 Install Doc, just posted a few days ago has the pulley info well detailed. See the Documentation tab at the top of this page