If you frequent any CNC Forums out on the ‘web you’ll find that these Chinese 3020 CNC routers are generally well received. It is also common opinion that the control electronics leave something to be desired. [Peter]‘s feelings were no different. He set out to make some improvements to his machine’s electronics such as fixing a failed power supply and adding PWM spindle control and limit switches.
[Peter] determined that the transformer used in the power supply was putting out more voltage from the secondary coil than the rest of the components could handle. Instead of replacing the transformer with another transformer, two switch mode power supplies were purchased. One powers the spindle and the other is for the stepper motors. So he wasn’t guessing at the required amperage output of the power supplies, [Peter] measured the in-operation current draw for both the steppers and spindle motor.
As received, the spindle speed is manually controlled by a potentiometer on the control panel. CNC Machine Control software, such as LinuxCNC or Mach3, has the ability to control the spindle speed by using PWM. It turns out that the 3020′s control board and spindle motor driver are designed to do this, it is just not hooked up. After some poking around on the board, all that was needed to finish the job was to add two jumper wires and flip one DIP switch.
The control board also has inputs for limit switches that are unused as shipped from the factory. Through some investigation it was found that the limit switch inputs are opto-isolated. Now the machine can be run without worry about unintentionally running out of travel. This and more is documented on [Peter]‘s site, including all of the parallel port pin functions and machine specifications.