PNC-300 CNC mill retrofit - IONI servo drive

I replaced the stepper motors that were used to drive the x/y table with Granite Devices IONI servo drives to drive new, new linear motor based, x/y table.

I found the xy table on eBay, and it was almost the perfect size to fit into the system. It has glass scales as feedback devices for the linear motors:


Encoder MSA 670.73

grating pitch 20 µm, times 10 (500 nanometer resolution !!!)

measuring length 170 mm

accuracy ±5 µm/m ( less than 1um deviation over the full travel length!)

reference index: center of the measuring length

supply: +5 V

output: square wave signals 5 V

The table did get banged up in shipping a bit, so it needed some TLC

Because of space issues, I used IONI servo drives, in IONICube1X motherboards.

The feedback connector on the IONI is the X2 connector:

X2 pinout

The glass scales are single ended and get connected to the X2 connector like this:

One problem with the IONICUBE board is that the voltage regulator does not fit my requirements.

It is a tight fit. Here, you can see the before and after fitting the servo drives:

Fitting the xy stage into the PNC300 also required some adjustments, but in the end it all worked out well:

The PNC works in steps of 0.01 mm, and so the 500 nm glass scales provide the servo 20x the resolution. This was verified to work with a laser interferometer:

Here is a hole that I milled into a piece of stainless, which to the accuracy of my calipers is exact.