To convert an existing milling machine to a CNC milling machine or buy cnc machine (ซื้อ เครื่อง cnc ,which is the term in Thai), the following are required in addition to the milling machine:
- Stepper motors and limit switches
- Stepper motor driver electronics
- Stepper motor control program
- CAD program
The Stepper Motors
For normal applications in the hobby area, motors with around 1 Nm, used in half-step mode, are usually sufficient. A claw coupling, for example, can be installed to connect the motors to the spindles. The bearings must absorb the axial forces of the spindle so that they do not affect the motor. Cheap stepper motors are always available as residual and special items in specialist shops, whereby the rated current of the motors should be 1 to 2A.
The Stepper Motor Driver Electronics
The necessary driver electronics decode the signals from the computer and control the current through the various motor coils on this basis. Driver electronics can be bought ready-made, but experienced hobbyists can also create them themselves with the help of circuit boards, component sets, and corresponding assembly instructions. Depending on the driver circuitry, it may be necessary to support the heat sink with an additional fan. The control program used specifies the cable assignment to the computer.
The Stepper Motor Control Program
A computer program controls the CNC milling machine. There are different programs to choose from, some as free downloads, some as purchase programs. The contour to be milled can usually be read in as an HPGL or DIN file. HPGL files offer the advantage that they can be created quite easily, but mostly not all axes can be used simultaneously. On the other hand, DIN files enable all axes to be traversed simultaneously but are quite challenging to generate.
The PC And The CAD Software
Most CNC programs run on a standard computer. However, it is advantageous if a game port is available because, in this case, the milling machine can also be operated manually using the joystick.
With the help of the CAD software, the desired contour is drawn and then printed in a file. When drawing, however, the diameter of the milling cutter must be taken into account or corrected accordingly using additional software.