Hi,

I’m starting the retrofit process of my 1995 Milltronics Partner 1 VMC control to a Kogna/Kmotion control. I’m also making a few modifications as part of the process. My goals are to end up with a more capable and reliable machine, and to understand it well enough that going forward I can improve and repair it easily without needing to source obsolete and expensive parts. I’ve attached an unfinished wiring diagram. Please excuse my terrible diagramming skills, this is not my strong suit. I still have a lot of stuff to figure out but I wanted to see if anyone points out anything wrong with the axis control and feedback portions of the project. There is a lot of stuff based on information from the original electrical schematics of the machine, and I expect to change some stuff as I go.

The machine had the Custom Servo Motors AC servo option, with a 12.5HP AC servo spindle and a max spindle speed of 4400RPM. In my opinion most of that horsepower is useless at that speed in a 4500LB machine, and I want more spindle speed. Most versions of this machine had a max spindle speed of 7500RPM, and I feel comfortable assuming that they didn’t make a special spindle for this option. I guess if I’m wrong I get to buy the spindle I want anyway. So I plan to make 2 custom poly vee belt pulleys that will fit in the head and allow 7500 RPM. I might make a Fadal style 2 belt speed change system. I’m still undecided on this point, I really am not sure I need the torque. I usually thread mill anything over ¼” anyway.

The only component other than the control that I really want to replace in this project is the spindle drive, I have had to repair it twice and it’s an expensive component that is no longer made. I think that the problems are the result of running it on a rotary phase converter. The spindle motor is a 12 lead wye parallel to wye series to delta switchable motor, with a system of contactors that switch the power leads for each configuration depending on the speed range. I reverse engineered the switching system in the hope of keeping the spindle motor, only to find out that the drive is also shifting the commutation signals from the resolver with the different speed ranges. I thought about a few kludgy solutions to emulate what the current drive is doing, but ended up deciding to just buy a new spindle motor. I found a 5.2kW Parker MPP AC servo motor and Parker Compax3 drive. This drive is actually a 480V drive that can run at 240V, so hopefully it will be more tolerant of my power supply. The smaller motor should be perfectly adequate for my needs, and I would be more comfortable running this machine and my big lathe simultaneously on the limited power in my shop. Hopefully I’ll be able to sell the motor, drive, and contactor setup and recoup some of my costs.

I ran into a bit of a stumbling block with the Parker servo drive, it turned out to not match the (Factory) label. The drive I have is actually the version with encoder feedback, not resolver feedback like my motor. So I could have tried to find a drive with resolver input, or a different motor. Both of those options looked more expensive than a $150 Pico Systems resolver-encoder converter, and the Compax3 servo drive manual explicitly states that it CAN commutate a motor with only encoder feedback. If this doesn’t work I’ll figure something else out. I can probably fit an encoder to the motor if I need to.

Motor Brakes: I got the servo motor for the spindle cheap without knowing everything about it, and was surprised to find out it is a braked motor. Not a big deal, it’s a 24V brake and I’ll connect the brake to +24V DC power directly. The motor contains a rectifier so the input polarity doesn’t matter and it shouldn’t need a diode across the leads. I suspect this is also the case for the Z axis motor because it’s based on a standard Parker motor as well, but I need to poke around to actually confirm this before I take things apart.

Encoders: I have all encoder outputs going to JP8. Axis drives simulated encoders: RS422 Output Drivers, 5v 20mA. Notation is A’, A, B’, B, Z’, Z. I have assumed that the Z’ (Index Pulse) signal can be connected to ground, and the Z signal connected to a 5v tolerant I/O pin on JP7.

Spindle drive simulated encoders: Less information here, but I believe the signals are also RS422 5v. Notation is A, A/, B, B/, N, N/. I see no use for the index pulse signal here, this encoder gives the spindle motor position which I do not expect to stay rigidly coupled to the spindle position (Belt driven spindle).

Spindle Encoder: It turns out my machine already has an encoder physically coupled to the spindle with a timing belt. I need to verify that the encoder actually present matches the wiring diagrams that I have. It should be a 500-count encoder with outputs labeled A+, A-, B+, B-, Marker +, Marker-. It has a +5V and a ground wire, so I am assuming an output of 5v or less. I want to use this encoder to position the spindle for tool changes. Rigid tapping small stuff would be a bonus, but I don’t need it.

MPG/Buttons: I want to keep the MPG on the front panel, along with some of the physical buttons. The MPG is apparently a 5V quadrature encoder. I also want physical knobs for axis select and step size. I am assuming that it won’t be too hard on the software end of things to treat 3 Kogna inputs as binary 1 or 0 and not have to run more than 3 signal wires for a 6 axis selector switch. I am also assuming that I’ll be able to have a momentary switch toggle an output to on or off in software.

Grounds: I am trying to avoid possible loops. Some of the grounds/commons on the drives are connected together internally, some are not. I am assuming that it doesn’t matter for the encoder index marker pulses if the Z’ signal is grounded at JP7 or at JP8. If it’s not OK, should I use 2 inputs for the Z and Z’ signals?

I am posting this to document what I’m doing and to see if anyone points out any technical mistakes I may be making before I find out the hard way. I do have some choices still to make that I am interested in feedback on though.

I have a nice, powerful CAD/CAM PC located right next to this machine. I have contemplated using it for Kmotion CNC with an additional monitor, keyboard and trackball mouse located on the machine. Alternately, I would buy a cheap micro form factor PC and install it in the enclosure that used to house a CRT monitor. I am having trouble deciding between the convenience of having all my files in one place and CAM at the machine, or the reliability of using a PC that isn’t connected to the internet. Either way, I will have a larger monitor mounted where the machine monitor is currently located. But I am also trying to decide if a touch screen would be a good idea. I know opinions on touch screens on CNC are divided, and I’ve never used a CNC with a touch screen.

So, in summary:

Did I make any stupid mistakes obvious to someone else so far?

Is the way I plan to connect the encoders Z index pulse correct?

Should I run KMotion CNC on my CAD/CAM PC, or buy another PC?

Should I get a touchscreen for it?

Thanks to anyone who takes the time to read this,

-Nate