CNC for Beginners Guide

  • What is CNC?CNC is Computer Number Controlled.
    This usually referes to a machine controlled by computer and software to perform a task
    This can be a multitude of machines or applications but can indclude computer controlled Laser Cutters, Plasma and Gas cutters, Wood Routers, Lathes, Mills and other machines
  • What advantages does CNC offer?CNC offers;
    repeatabilty i.e many parts can be made the same
    Complex shapes and parts that would be hard or imposssible to make with manual Lathes or Mills
  • So how does it work?You create an electronic file of your work in a CAD (Computer Aided Design) programe. This can be as simple as a line drawing
    The control software then takes this file and converts it to a series of commands to machine your part. When executed the machine will operate as instructed moving and maching to produce the part.
  • How does the machine move?There are several control systems possible but for the prefered system used by is the use of stepper motors.
    A steper motor is a special motor with coils to allow the motor shaft to be turned a specific ammount.
    The coils are driven is a specific order to allow direction control and control each step. In simple terms one pulse moves the motor shaft one step which for most motors is 1.8° (200 steps per revolution of motor shaft)
    This method means when the software sends a known number of pulses the machine moves a known and defined ammount
  • So how does the machine connect to the computer?The computer software sends out the motor step pulses out a port, most commonly the computer parallel port.
    The usual standard is two data lines per axis, STEP and DIRECTION An external piece of hardware is required to convert these low power computer pulses into high power pulses able to drive the stepper motors.
    Most software and some hardware will also offer additional inputs and outputs for control of limit switches, emergency stop, spindle motor control and coolant pump.
  • What does the Stepper Driver do?To convert to high power pulses some hardware called a ‘stepper driver’ is used and is sized to suit the motor i.e. current
    The stepper driver also does the work to pulse the motor coils in the right order for direction. Good Stepper drivers also have current choppers (limit current) and offer microstepping. Current chopping maximises motor shaft speed and Torque
  • What is microstepping?This is where the stepper driver with special control can step a stepper motor less than one step giving more steps per motor revolution
    For example with 1/12 microstepping the driver will move the motor shaft 1/12 of 1.8° per pulse from the computer
  • What is a breakout board?A breakout board makes a connection to the computer, often the parallel port and breaks the connections out to accessable connections, maybe screw terminals.
    A good breakout board will be opto isolated. i.e. electrically isolate the machine from the computer
    A CNC Controller is a integrated product of a breakout board and stepper drivers in one
  • So what software can I use?We recomend Mach 3 for controlling the machine using G-code
    It is fully functional (with file size limit) and free to try and as well as including basic CAM software to import from your CAD files (DXF)
  • Still confused? Need help?Get in touch, we may be able to help