Im currently converting  A 10x22 lathe and am using digital steppers 8056D and a c35 bob. My question is I would like to control spindle speed and also do some threading through Mach,
but am unsure on which board to use c6 variable speed control or c3 index pulse card with my Teco VFD EV series. And also what would be the best way to wire them to the vfd ??
Any help or suggestions would be greatly appreciated .   

You can do threading with just the C3 but the spindle speed would have to be controlled manually at your VFD.

If you want to control the spindle speed from within Mach you'll need a the C6.  I have a C11 which combines a B.O.B. and speed control and I also have a C3. The C3 works great but so far I haven't been able to get the speed control portion of the C11 hooked up properly and working.

Good luck and make sure to post details if you get a C6 and get it working.

I have the C3 Index pulse hooked up to c35 and have all boards powered up. Does the c6 board go in the output on c35 via rj45 connector and will this power up the board?
And also does c6 need 2 terminals (gnd and 0-10v ) hooked up to com and 0-10v multi function analog output on my vfd to get mach to control spindle.This VFD has very poor literature so this is a little mind boggling.

Heres some photos

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