The step-by-step methods used to construct a basic CNC mill are a useful example of how computer controls can be applied to a relatively small machine. In addition, home CNC machining projects illustrate the fundamental principles by which most computer programmed controls operate. As with any do-it-yourself project, however, it is crucial to first obtain the proper skills and training necessary for working with CNC equipment. Personal preparation and observance of safety protocols are important, as is the close adherence to manufacturer recommendations before attempting to construct or modify any device.
Preparing the Components
Assembling a home CNC machine requires a particular set of components, most of which can be purchased from hardware suppliers, obtained from surplus devices, or built with commercially available products and tools. While there are numerous variations on the types of components that may be used, as well as a wide range of different combinations for them, the following list of parts may be used as a general guideline:
• Stepper motor: This is a relatively high-torque motor with multiple coils and wires, and is available in both unipolar and bipolar configurations.
• Drive screw: The drive screw can be made from a threaded metal rod coupled with a complementary nut to reduce drag.
• Linear Slides: Linear slides may be taken from a multi-axis cutting table or manufactured from machined steel with ball bearings and an angled roller.
• Controller: The controller unit regulates the machine’s motors and provides an interface for the operator. For a more detailed list of the components used in its assembly, see “Components for a Do-It-Yourself CNC Machine.”
Assembling a Controller Device
Assembling the controller unit for a home CNC lathe or mill largely depends on putting together translator chips and networking cables that will be linked to the motor. Do-it-yourselfers often use standard 8- or 16-pin sockets to mount the translators onto a pre-printed and drilled processor board. The controller can then be attached to a parallel port array with soldered connections.
A typical stepper motor has four electrical coils with six wires attached. Each pair of coils has corresponding common and dedicated leads. The resistance between the leads can be measured by a multi-meter in order to identify each wire. The resistance across a set of coils is generally double that of a single coil and wires connected to separate coil pairs will provide higher resistance as well. In some cases, the motor may have linked common leads. There are normally six output connections on a controller unit and a group of three wires should connect to each pair of coils on the motor.
Before beginning work on the structural components in a small CNC machine, it may be helpful to invest in a couple of sturdy cutting boards for use as workpieces, as well as a sharp table saw or circular miter saw. The threaded rod must be able to move within the motor apparatus while also being anchored for stability, and ball bearings can be used for installation. First, holes around the same size as the diameter of the ball bearings are drilled into the cutting board. Next, a slot is cut using the miter saw, and a machine screw hole is drilled into the cutting board workpiece. The ball bearings are positioned between nuts tightened along the threaded rod with a wrench, and the machine screw and bearings are secured into the machine block.
The Mechanical Frame
Constructing a mechanical base usually requires some careful design planning to evaluate the overall size of the finished machine and the subsequent amount of material that will be necessary to fabricate it. Measuring the machine’s axes and positioning the components is one way of planning the layout. Next, the table or miter saw can be used to shape the cutting boards into pieces for the machine’s framework. A flat base can serve as a foundation if holes are drilled for machine screws to be threaded into the material. A bearing block can be added into the rectangular frame once holes have been drilled and rods are installed to maintain the structure’s integrity.nyc
The Upper Axis
The upper portion of the CNC machine can be constructed with a pair of simple sliding rails or with a larger slider at the base. A three-sided tower can be attached to the edge of the base, with the center piece shaped from the same cut as the bottom section. To drill more accurate holes, screw the pieces together first and then use the drill press to make mounting holes. The central sliding device must have holes aligned for both the slider and the threaded rod, while a nut can be used to properly secure them. Using a sander or other smoothing tool to contour the sliding unit can make it easier to mount without weakening the stability of the metal components.
After the slider has been installed, the holes for the axes need to be drilled and screws may be used to position them. A dremel shaft can be used to create a mount for a rotating tool, and one with greater flexibility can help reduce vibration. Motor mount brackets will serve to secure the stepper motors in place. Finally, after these components have been fitted together, various CNC software programs can be set up for use on the machine. The controller interface allows the user to control the machine through these computer programs.