CNC Gantry Router (PrintNC CNC)

Background

The PrintNC CNC is an open-source project for a CNC gantry router. The design for the machine itself was provided by Mark Hogan. I had to build the mechanical and electrical subsystems. As well, I had to program the CNC using LinuxCNC as my controller. The majority of the design was finalized when I started the project, but there were a few things I had to design: sensor mounting, electrical box wiring, cable track mounting, and the enclosure.

Mechanical Subsystem

I chose the PrintNC as my CNC project because of the mechanical backbones. It utilizes rectangular hollow steel tubes and steel-steel connections throughout. My concern with other options in my price-range was the use of thin aluminum or 3d printed parts for critical components. The use of steel-steel connections increase the rigidity of the machine and allow future improvement/upgrades to be made and be worthwhile (new mounting, flattening mounting points, more rigid supports). The CNC uses 20mm linear rails and 16mm ballscrews on every axis. The original design uses a pair of carriages for each axis rather than the industry standard of two pairs per axis. This was included due to easier assembly for inexperienced users who are unfamiliar with machining or precision component alignment.

Future plans for myself include upgrading each axis with two pairs of carriages and preloaded ballscrew nuts to reduce backlash. The idea though, is that once you have an operational CNC machine, these upgrades become a lot easier to complete.

Electrical Subsystem

The electrical subsystem was partially designed by a member of the PrintNC CNC community named Logan. Due to my inexperience with electrical systems and the potential safety hazards when working with 110VAC and 220VAC, I utilized his design for the latching circuit and Estop. The electrical components are organized into two boxes, high and low voltage. The high voltage box contains all of the AC electrical components, and the low voltage box exclusively contains DC components. This separation is necessary to prevent noisy AC signals from the Variable Frequency Generator (VFD) or other AC signal lines from causing issues with the stepper drivers or the MESA 7I96 controller board.

The wiring could use some tidying up, but the device is functional and in use as is. Future upgrades to the electrical subsystem would include replacing the open loop DC stepper motors with closed loop AC servo motors.

LinuxCNC

This the component of the CNC build that I overlooked the most. It was the greatest cause of headache, but initially the one in which I was most confident. LinuxCNC is a CNC control module that operates using a Real-Time Kernel of Linux. To get this system working, I had to learn a variety of things about how Linux operates and how to configure LinuxCNC INI and HAL files to integrate the sensors, motor control, and programming. LinuxCNC is the program that runs on a desktop computer and then the computer is connected to the MESA 7I96 controller board which handles all most of the sensor integration and enables better real-time performance.

Enclosure

One of my biggest interests in all things related to sounds and vibrations. I love to design and build speakers because of all the work involved with managing audio sources. As well, I have a general interest is noise management with a lot of my various tools and machines. As such, the CNC enclosure was a rewarding design and fabrication process. I wanted the enclosure to be inert and quiet, so the walls use similar construction to house walls and are filled with multiple layers of drywall and sound damping underlayment. The top layer of drywall is composed of two pieces of 5/8" thick drywall with a layer of Green Glue in between. The green glue is a damping compound that helps to reduce the transmission of sounds through materials by converting panel vibrations from mechanical energy to thermal energy.