What type of VMC do you have..?

It's a 1983 Roku Roku MiniMac.

Have you thought of sticking with the Fanuc DC drives..they are very cheap to buy on Ebay these days and the Fanuc manuals are very in depth on how to set them up.
I've found them to be very reliable...

I am at the point where the machine just needs to be reliable.  It is 26 years old and in the 3 years that I've owned it, I've had more than my fair share of gremlins and downtime.  I have intermittent 401 alarms (among other random problems), which could be the drives, the wiring, the controller, etc. - I just want it to be reliable.  The machine is finally making some money and I cannot afford to have it randomly drop out.  By gutting everything, I can be sure that I get all of the gremlins.  Plus, the project will be a bunch of fun.

On the Fanuc system (I presume you have 6MB??) the encoders attach to a frequency to velocity circuit on the motherboard to give speed and position.

I'm fairly new to Mach..how will you set up the encoders, i'm asking as I have a Galil DMC 1880 that I would like to set up with Mach3 and the Fanuc yellow cap dc brush motors.

Yes, it is a 6MB.  I will be using Galil DMC-2153 controller (the extra axes for future projects, such as a rotary table) connected to three AMC BE25A20AC drives.  I haven't checked if the Fanuc encoders are 5V TTL style.  If not, I will retrofit some USDigital units on there.  It won't be the first time I grafted different servos onto a motor...

The project is on hold for the summer (too busy), but once I get started, I will begin a blog.

Thanks for the interest,
Chris

I have never come across any Fanuc that did not use 5v for  encoders, differential 2000p  or 2500p/rev were most common.
Some 6 used resolvers so I imagine you have checked that.
Nosmo

Looking forward to seeing some pics of your machine as the project unwinds . The Fanuc motors are very good quality and work really well in my experience...after all they are still making money for you 26yrs on!!

The 401 alarm is usually motor related ie. a build up of carbon dust and damp in the motor or in extreme cases can be a faulty tacho or encoder but this is quite rare.
Slop in the motor bearings can cause this too if the windings are moving about too much.
Good thing to check the brushes for wear although i'm sure you already have this under control!!
If the motors are left standing for a long period the brushes can rust the commutator too..been there done that!!

Will you be using the Fanuc spindle motor and drive..? Would be quite expensive to replace ! I'm presuming its a Fanuc AC model 3 or above with an A06b-6044 drive..?
Not sure if you can rigid tap with the Fanuc motor by adding an encoder..? I think the motor uses a Tacho for speed.
Mine has a resolver to position the spindle for a tool change (M19) as well.

John.