Spindle speed fedback?

[Hood]

Oh just to add a bit to the VFD route, if you oversize the motor and VFD then you can compensate, to some extent, for the loss of torque at lower revs.
Hood

[Katoh]

Hood Cant thank you enough
That's just a wealth of knowledge, Your on money when you say its money driven, I just did some searches then and AC servos are not cheap by any means of the word.
A good lesson is be learnt here not to just jump in with two feet, I have put on some bids on bits and pieces and if won  I am committed, so I will be heading down the the VFD  Induction motor road. but I always have a whopping great wood lathe here that's crying out for something special as well. I will keep my eyes open like you for a bargain in the servo world, I see its a much better option.
Do you run the servo through a VFD or just straight 3 phase?
Katoh

[Hood]

Just take care with any servos and drives you are looking at as you will really need ones that can accept Step/Dir inputs if you are planning to use it as an axis. Also care needs to be taken that the AC servos and drives match as often the encoders have commutation on them and the drives need to accept the same type of commutation signalling. Best to get matched motors and drives unless you know what you are doing, also watch out as some AC servos have resolvers and not all drives can accept resolver feedback, I have swapped out resolvers for encoders on some motors before and its fairly easy if you have a dual trace scope. Some drives can do self sensing for the commutation but that will require they move the motor a bit (12 to 1 turn) to find find the motors coils each time you power the drives, unless you keep the logic side of the drives alive when you power down the main power side of them.

I have mains 3 phase in the workshop, VFD wouldnt be any use for powering the drives, you would need a rotary phase converter to get true 3 phase from single phase mains for that.

Hood

[Katoh]

Again Thanks hood!
I have 3 phase power as well, which I use to drive my Fimec 3.5kw spindle on the router , its just easier moving the single phase stuff from place to place, that's all. You have totally lost me on encoders/ resolvers, ect. I see a few nights coming up with some heavy study, trying to sort this out.
Katoh

[Hood]

You will be doing well if it only takes a few nights

Hood

[BR549]

IF you  use a 4pole(1800rpm) mpotor they have more torque down low.With the VFD you can overspeed it up to the 3600 level as well. SO that gives you great low end and good top end torque.

Just a thought, (;-) TP