VFD Choices

[DieselPower]

I just got a series 2 Bridgeport and am re-doing the controls. I only have single phase in my shop and have 3 VFD's running already and am very familiar with them. What I don't know much about is CNC control of a VFD. I want to be able to do ridgid tapping. Should I use a vector VFD that requires an encoder to operate, and put an encoder on the spindle, or can I add an encoder later and just tie it into the machine control with a standard VFD? Which one will give me more options? I'm leaning towards the vector/encoder VFD type, like this one.
http://cgi.ebay.com/7-5-HP-230V-VECT...d=p3286.c0.m14

I would appreciate you guys thoughts on this.

[Al_The_Man]

You did not say what Controller you have?
AFAIK, Mach does not do rigid tapping?
Commercial machines use a spindle motor with fairly tight control, this means either a pulse wheel or encoder on the motor shaft for precise speed control.
The Z axis is then geared to the spindle rotation via an encoder driven off the final spindle shaft.
Al.

[DieselPower]

Planning on EMC2 at this point. I would use a 5000 PPR encoder on the spindle shaft only.

[Al_The_Man]

Well if EMC supports it you maybe in luck, personally I would prefer to have one on the motor as well, the VFD link mentions that it has encoder option, does this mean it is a must with this model or will it operate without it in the vector mode in the mean time?
Also, maybe a query in the EMC forum as to rigid tapping may help.
Al.