Mach3 machine, some questions.

The spindle driver is some weird (undocumented) BLDC unit with a motor using hall sensor feedback.
This benchtop mill has the tool spinde parallel to the motor and a short 1:1 toothed belt transmission. Amplifier works I can spin it up connecting 5V to signal wires.
How to connect wires, power supply and HAL components is another story.
Probably similar to a frequency inverter.

I am using the old transformer, which includes a AC to DC rectifier board.

You say LinuxCNC is way way better than Mach 3.

How so?

As far as I could research, Mach3 is not able to do fully closed loop operation with feedback between motor axis and rotary or linear encoders.

• feed rate based on spindle power (cutter breakage detection)
• EDM with reverse movements or slow down based on electrical values
• a hobbing machine that slows down workpiece spindle and tool spindle in case something reaches the limits.
• Turning excenters or augers on a lathe
• cam shaft grinding
  
  These are examples I can think of. Things that Mach3 could not provide, according to my understanding of the available information.
  Of course those items go bejond the average DIY user and will not be easy to do. Not easy to do in any system, unless available as turnkey in exchange for $$$
  
  Linux CNC seems to be in the gap between, "very basic good enough" and "just pay money to one of the usual suspects"
  
  I see a lot of misconception that Linux CNC ist "Parallelport technology" for 3-axis open loop stepper machines. Which is actually only the lower end of the spectrum.

You say LinuxCNC is way way better than Mach 3.

How so?

A work in progress by a user in NZ but try commanding a pallet changer on a horizontal 5 axis machines like this in Mach3.

This machine fills a shed.
Many people use Linuxcnc to retrofit big commercial machines because of its flexibility and extensibility.
Here the user had hit the limits of using classic ladder and wrote a custom Linuxcnc C component to do this. A week earlier, he knew nothing about programming and is now loving it!