Wednesday, 4 June 2014

Adventures in CNC - Part 7

CNC Electronics - Gathering The Components

New here? Check out PART 1

Now that the body of the machine is coming together nicely, it's time to focus on the 'Brains'.

In order for a CNC router to do anything useful, it will need....

Controller board/Breakout Board

The Breakout Board has two important jobs. It translates the commands from your computer into signals that your CNC motors can understand. The second job is to electrically isolate all your crazy CNC stuff from your delicate PC. If something goes horribly awry, you may blow your board but the PC should be fine. These boards tend to come in Parallel Port versions and newer USB versions. The unit that came with my machine is a generic Chinese parallel port version. The instructions are a little thin but it seems to work well.

Stepper Motor Drivers

The Stepper Motor Drivers receive step and direction signals from the Controller Board and send out pulses of the correct voltage and current to run the motor. The drivers have a set of DIP switches that set options such as the maximum amperage out and 'Microstepping'. Microstepping allows you to turn the motor less than the normal 1.8-degrees it would normal turn in one step. This allows greater accuracy and smoother motion.

Breakout Board (top) and Motor Drivers (bottom)

Power supplies

There are three different voltages that were needed for my system. 48 Volts for the motors, 5 Volts for the Breakout Board, and 12 Volts for the Proximity Sensors. My machine came included with a 48V power supply that is fed to the motors through the motor drivers. I added 5 volt and 12 volt 'wall wart' type supplies for the additional voltages.

Stepper Motors

Three Wantai Nema23 3.0A 270oz-in 1.8-degree/step Stepper Motors came included with the kit. The term Nema23 tells you the spacing of the holes on the motor mounting plate. The 1.8 degrees/step tells you how many degrees the motor with turn with each step. If you divide 360 degrees by 1.8, you can calculate that the motor will take 200 steps to complete one revolution.

Stepper Motors - The tape flags are for testing

Machine Control Software

For Machine Control Software, I purchased a copy of Mach3 from Newfangled Solutions. This seems to be the most popular CNC control software out there. The cost was $175 US.

Proximity Sensors/Limit Switches

Limit Switches are set up to be triggered when an axis of the CNC reaches the end of its travel. This is important to protect the machine from damage. These can be simple mechanical switches or Inductive Proximity Sensors that detect the magnetic field of the metal machine parts without actually touching them. The kit I purchased included five Inductive Sensors.

In the next installment, we'll put these parts together. Stay tuned!


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