Making A CNC Milling Machine – CNC Electronics

Part 4

 CNC Electronics.

Making a CNC Milling machine requires you to learn a little bit about CNC electronics. Every CNC machine needs a control box with electronic components which converts electronic signals from the computer into movement. There are many different types of electronics available for CNC.  Most of the electronics fall into three basic categories; motors, control boards or power supplies. Let’s take a look at the CNC electronic components I selected to help make a CNC milling machine.

Types of Motors

A CNC milling machine generally  have one of two types of motors; either stepper motors or servo motors. Servo motors are generally more expensive and more sophisticated than stepper motors.  Servo motors are a closed loop system with special sensors which monitor how far the motor turns.  Servo motors are more accurate and repeatable than stepper motors, but they cost nearly three times as much.

Stepper motors do not use a sensor to monitor their movement.  This makes them easier to install but less reliable.  However, stepper motors are good enough for over 99% of what I plan to do.  So I chose to use stepper motors.

Stepper Motors

The Z axis Nema 34 Stepper motor is huge compared to the two Nema 23 motors.

For the X and Y axes I chose to use a NEMA 23, 570 oz./in.  motors from Automation Technologies Inc. The NEMA 23 motors have plenty of power to move around the milling table.  But the Z-Axis head assembly is a different story. That’s why I chose the Niman 34, 906 oz./in.  motor.  It has nearly twice the lifting ability of the smaller motors.  The NEMA 23 motor would work but I decided to give myself more margin for error.

Control Boards

My CNC controller has three types of boards.  The driver boards, breakout board, and a motion control board. Each of these boards performs a different function in the CNC control box.

Driver Boards

These Digital CNC Driver Boards have built in heatsinks.

Driver boards convert electronic signals from the computer into electronic pulses which make the motors move.  The driver boards I chose are digital driver boards instead of analog.  They have computers built into them which convert the signals. There are many types of drives is available so it is important that you choose the driver that is a good match for the motors you intend to use. You choose a driver based on the voltage and the number of amps they can safely control. A higher voltage or amperage could be needed for larger stepper motors. Most driver boards and stepper motors will list their requirements.

Breakout Board

C32 Breakout board with RJ45 inputs.

A breakout board is an interface board which allows all the wiring from the components to connect in central location. The breakout board can direct the electronic signals from one component to another. For example an input switch could trigger an event like a motor turning off. The input signal would come into the breakout board and be transferred to a solid state relay which would shu off power to the motor.

Breakout boards come in many levels of complexity and price. A simple board with minimum features can cost as little as $10. Advanced breakout boards can cost as much as $1000.

The Breakout I chose is the C32 board from CNC4PC.com. This board cost $186. One of the main reasons I chose the C32 was because it uses RJ45 connectors to wire the components. This allows you to use Lan cables to connect the components. Having one type of connector for most things really simplifies wiring the control box. The C32 also has a connector built in to accept the Smooth stepper motion card (more later). Her is a list of the features of the C32.

Features

Connects directly to the Smooth Stepper, RJ45 connectors for all I/Os,  IEEE 1284 Standard compatible, Works with regular parallel ports, Has a relay that reflects the status of the e-stop button, Built-in Safety Charge Pump, Built-in Variable Speed Control, Two Built-in 8 amp Electromechanical Relay with NO and NC positions, Optoisolated inputs, Monitors E-Stop, Safety Charge Pump, and Drivers (it only monitors G320/340, DG2S and Viper Servomotor drives at this time),  Buffered outputs,  34 inputs and outputs on 2 ports.

 Motion Control Board

Ethernet Smoothstepper Motion Control board

Motion control boards are used to replace parallel ports and allow connection to USB or Ethernet ports. The motion control board also processes the signals that your motion software (Mach3) produces and optimizes it to give you a smoother cut. One popular motion control board is The Smoothstepper from Warp9. I have been using an Ethernet Smoothstepper for over a year now and really like it. For more details on motion control cards you might want to check out this blog post. MOTION CONTROL.

Smoothstepper is not the only motion control card available. In fact there are several new motion cards on the market. Some of these new cards incorporate a breakout board along with the motion control features. I expect to see more motion boards incorporate additional features in the future.

Safety Components

The electronics components we have mentioned so far will provide the basic functions of your CNC machine. However, to have a fully functional machine you will need to add some safety components. Safety components will protect the operator and the machine from damage or injury. Common safety components include Emergency stops, limit switches, charge pumps and cut off switches.

Since safety is such an important topic I will cover safety components in another post.