Previously you could do that but not sure if you can now if you need G95, I cant remember exactly but I know when I was testing a new revision I had problems. After a lot of investigation it turned out that it was because my M3 and M4 macros (they were custom macros to suit my lathe) didnt have DoSpin(CW), DoSpin(CCW) in them. Now whether its still the same I dont know as I now have a servo on the spindle so the macros have changed to standard ones.
 Wont do any harm giving it a try.
 As for M7, M8  then you could write your own macros for them to do what you want, I did and still do on the lathe, just have to make sure you dont have the flood/mist relays enabled on Ports and Pins, Spindle setup.
 Then again if you are only using the M3 then why would you need to use the M4 just so you could use the OutPut, it would be easy enogh just to make up a custom macro to use that output and call it in your code, I presume you would have to manually edit your PP or code to put in M4 when you wanted to do whatever you want M4 to do, so why not just call your macro M104 (or whatever you want) and name your custom macro as M104.m1s.

Hood

I assumed that M3 and M4 would have anti-coincidence built into the code to fault but didn't check that out. I see what you mean though. I had a need for M7 (M107), a sort-of harmless M code, so have used it elsewhere. I was afraid of messing with M4 so went ahead and used it as Mach intends.

Bill C.

But, only utilizing M3 for the spindle (with M5) and controlling spindle direction with an external switch or controller, why could you NOT utilize M4 for another totally different function? Ray L. eludes to the ability to change M4's function in the main directory and writing another macro to perform a function that includes M4. Looks like a fault would occur only if the established function were not modified. The same for flood and mist M codes. Why waste an output for mist when you only use a flood coolant system? This would require some diving into the workings of Mach but can't it be done? You can always reload Mach if it gets too crazy.

Thanks,
Bill C.

Since you can define the functionality of M3, M4, M5, M7,M8 & M9 through the corresponding macros, I think you can make them do whatever you like, but I don't think it's a great idea.  If nothing else, it will be completely confusing to anyone looking at your code, or using your machine.  You'd have on-screen buttons whose functions are quite different from their labels.  I would instead define completely new M-codes, and use those instead.  The resulting functionality will be the same, the effort will be the same, and it'll make sense to others, so you might as well follow established standards. 

Regards,
Ray L.

This is toward another use for Mach3 and I should probably start another thread on this. This Electron Beam Welder is presently using a Visual Basic written operating system which is cumbersome on a perfect day. I've used Mach enough at home that I see so much more sophistication than is even remotely possible with this present system. Mach would be changed enough that it would not be similar to a milling machine or lathe - etc. This welder has no spindle or coolant but has beam current and beam focus. The G-code programs are very similar otherwise and I have written a couple of pp's to work with it using KeyCreator.  Anyhow, when the time is right (and I understand Mach to a much greater degree) maybe can start another thread on this. These were questions pertaining to this situation but still toward my home use of Mach as well.

Thanks very much,
Bill C.