Excello Knee Mill Retrofit

I have an Excello 3 axis CNC knee mill with a Centroid CNC4 controller. It came running perfectly from an auction and I have been using it for years. The mill and controller were built in 1991 so things were a little dated.

Excello 3 axis CNC with Centroid CNC4 controller
Excello 3 axis CNC with Centroid CNC4 controller

I grew tired of the non-graphical interface and command line operation.  Luckily the 286 computer that handles the communication with the proprietary Centroid CNC4 computer gave up the ghost.  After requiring more than 20 minutes to boot for 6 months it began to freeze up while the programs were running.  That was bad.

5 Centroid 286 computer
Smoked 286 computer

Dead 286 computer.

Servo to stepper adapter
Servo to stepper adapter

This is the part I was attempting to machine when the Centroid controller decided to stop responding to commands.  So, a great reason to update an obsolete system.

I tried to see how to reuse the Centroid  driver boards and such for a while.  I gave up after discovering that the proprietary computer was partly on the computer board and partly on the driver boards.  Time for some new electronics.

The mill uses 8 amp steppers for each of the three axis.  I decided to reuse the steppers but throw everything else away.

 

Chinese drivers and BOB
Chinese drivers and BOB

I got 4 Chinese drivers with a breakout board off ebay.  The drivers are the DM860A.  The were originally described as 7.8 amp drivers.  After I ordered them the vendor contacted me and said they were 7.2 amp.  And he gave me a discount for the order.  Later I learned that the drivers were 7.2 amp max and 5.6 amp RMS.  Turns out Centroid rated their drivers the same way and the drivers are pretty much the same as what I had before. I am using a 80 VDC power supply from Antek.  At 80 volts and 10 amps it is probably overkill. I tested the set up with some 8 amp steppers from the scrap bin.

Old power box on mill
Old power box on mill

I gutted the power box on the old mill for a place to install the new electronics.

Cad layout of components
Cad layout of components

Tried to layout the new power panel on the computer.  It was only good for giving me a warm fuzzy that there was enough volume for everything. Too much effort for the payback involved.

Power and Control schematic
Power and Control schematic

This is a schematic of the power and control system.  It is a little outdated as some changes were made during assembly.

 

Blank panel
Blank panel

A clean blank panel to layout the components on!

 

Components on panel
Components on panel

The components were laid out on the panel.  My son Michael wired up everything for me and then we tried it out with the 8 amp spare steppers.  It worked first time out of the box!

Panel in mill power box
Panel in mill power box

Got the panel mounted in the power box of the mill. Cut some holes in the box for fans.

 

Mill with new components.
Mill with new components.

Hooked up everything and got it running.  Not quite as quickly done as the bench test.

LinuxCNC
LinuxCNC

I am using LinuxCNC on an older PC running Ubuntu 8.04.  The computer has a single processor and the LinuxCNC included on the 8.04 distribution is built to run a single.  Newer versions are available for multiple processor computers.  The computer talks to mill via the parallel port to the breakout board in the control panel.

I have used LinuxCNC with the ORAC CNC lathe for several years and it is much nicer than the 1991 software.

Machining the adapter
Machining the adapter

The software was installed and the mill parameters calibrated.  The adapter was remachined using LinuxCNC.

Servo to stepper adapter
Servo to stepper adapter

Part turned out nice and I get to watch the backplot on the screen as things are machined now.

Things not yet complete:

Cardboard fan shroud
Cardboard fan shroud

Forced air cooling to the drivers amplifiers is required.  Currently this shroud is cardboard as I await a 3D printed shroud from our developing 3D printer capability.

Fan shroud
Fan shroud

This is what the fan shroud will look like after it is printed.