Vetical Mill Retrofit - Component Assessment

I am just starting to look at retrofitting my current vertical mill. The Dynapath Delta 20 controller on my Tree Journeyman 325 is dying so I am evaluating a retrofit vs spending money on keeping a dying patient alive. Putting my time into the project is not a big concern, it is the cost of all the hardware I might need which is going to be the deciding factor. Currently it is the controller which is dying, but the axis servos and their driver boards are good, and the spindle driver and motor is also good. I am still trying to figure out what spindle drive I have since all the covers and nameplate were removed by the previous owner, but the servos are DC. Through my trouble shooting efforts to provide CPR to my dying Dynapath, it appears that the only communication between the Dynapath and the servos is a two wire connection for each axis over which a differential voltage is provided which results in the axis motion. The servo feedback, like from the tachometers, appears to go directly to the servo driver boards, not the Dynapath. I also know from having replaced the spindle control last year on my Trak 1630 lathe, that the spindle drives usually control spindle speed in response to a single applied voltage. If I perform my retrofit by separating the old from the new at these interfaces, I would think I could do this retrofit fairly easily and without a lot of expensive equipment replacement.

Before going down the retrofit path, I need to understand everything that will be required. Once I have the hardware side figured out, the software and UI side I think I can handle. Breaking the project up around operational lines, I have all the ON/OFF components which would handle limit switches, misters, etc., and then the linear drive components which handle the axis movements and the spindle speed. I have seen breakout boxes which can handle analog on/off operations through the parallel port or through the USB interface and this type of wiring and programming appears to be similar to PLC programming which I did years ago so it should not be too difficult or expensive, and does not scare me.

My main concern is the cost and approach to handling the linear operations which would include driving the axis servos and the spindle. It seems to me that all I need to do is get a PC running which will output four voltages, one for each axis position, and one for the spindle speed and I can use all my existing hardware for the axis movements and the spindle speed. Of course I need some magic box which will interface with the PC and generate these four sets of voltages. I have read where some people are replacing their servos with stepper motors, or installing encoders on their existing DC servos and purchasing new drivers, but if my current components are working fine and respond well to the differential voltages that the Dynapath is (or more precisely was) generating, why do I have to change out that equipment if I can provide the same differential voltage signals that the Dynapath provides?

Is there something that I am missing in my understanding of how to perform these retrofits?

welcome ,
As a Retrofitter , i'd go with a Mesa interface , keeping the original servo amps and spindle controller etc ,
one area to check is the type of encoders fitted , being either quadrature encoders or Resolvers , ( they are different ) this will be needed to be known as it has a bearing on the interface card required . ( and why I have not mentioned particular ones )

apart from the possibility of fitting a 5v & 24v dc power supply , you should not need much more ,
limit and home switches will require a little rewiring
overall it should not take too much time to convert , they are relatively straightforward

pm me and I can help you further if needed .

Thanks for your input CNCBasher. I had to go out and re-examine the mill to figure out your comment about the encoders. Originally I thought the only control signal for the servos from the processor was the single differential voltage wires going to the drive boards. I missed seeing the feedback signal from the encoders returning to the processor because they went to another board in the processor. I have a fairly complete set of blueprints for the machine and I found the wiring diagram which calls out the units as encoders. Can someone tell what type they are from the wiring diagram in the attached pdf file, or do I need to visually inspect the encoders themselves for a nameplate. If a visual inspection is required, what am I looking for?
Thanks.

From that they look like standard differnential 5v encoders with index signal, and should work perfectly with Linuxcnc (once you have the right hardware to plug it into). I'd suggest a Mesa 7i77+ the appropriate card to plug in to your PC (like a 5i25). There are other options from Mesa and other manufacturers as well.

Here are my pics of my Journeyman 200 R resolvers. Look to see if yours are different. I believe resolvers have 3 pairs of wires.

oupower.com/index.php?dir=_My_Projects/_...%20Machine&PageNum=7

Hi

Most DynaPath 20's used encoder feedback. Look for the axis drive motor (most likely either a Baldor or SEM) part number, embedded in the part number will be the number lines the encoder has. Most of these old systems had rather low resolution that is helped by the more modern method of counting encoders on each edge. The axes drives are most likely a Westamp or Servo Dynamics, they are +/- 10V input and the design is still sold by Baldor.

John