Week 07: Computer-Controlled Machining

Group Assignment:

• do your lab’s safety training
• test runout, alignment, fixturing, speeds, feeds, materials, and toolpaths for your machine

Fab Lab Bali’s CNC Machine Specification

Our CNC machine is a custom-made three axis hobbyist machine that uses Arduino CNC shield as a controller and Makita 3709 router as its router. It operates on GRBL - a free and open-source firmware that translates G-code instructions, which define the toolpath for the CNC machine, into specific movements for the stepper motors. These motors control the movement of the cutting tool or workpiece in a CNC machine. It’s a set of instructions uploaded to the Arduino that transforms it into a CNC controller.

Safety Rules

Personal Protective Equipment (PPE)

Always wear:

• Safety glasses: To avoid any material chips and debris hitting your eye
• Ear protection: The spindle of the milling bit that accelerates the end-mill in a very fast speed can be very loud as it cuts through the material. Always wear an ear-plug or a muffler to avoid hearing loss.
• Appropriate clothing: Avoid loose clothing, dangling jewelry, and gloves that could snag. Wear closed-toe shoes.

Steer Clear Ahead

• Make sure that you have enough clear space to walk around the machine. Avoid loose cables.
• Since the cutting job will cause dust and material chips to fly away - make sure that there is proper ventilation and vacuum to suck up the debris
• Be aware of where the emergency button is located. Make sure that you are of close proximity to the button.

Setup

Inserting Endmill

To attach our 6mm, 2-flute carbide, down cut, flat end mill to the router - we will need a 6mm collet with a matching 6mm/6.35mm nut. Make sure that the router is firmly attached in place.

Preparing Material

The work area of our machine is 1130mm x 1080mm - our sacrificial board area. Secure the material that will be used for cutting with screws and clamps. Make sure that the sacrifical board is level and straight. In this job we used an 18mm plywood.

CAM

End-Mill & Cutting Data

Insert our 6mm, 2-flute carbide, down cut, flat-end mill bit to the tool library. The makita router has a fixed spindle speed of 30000 rpm - so we adjusted the other settings to meet the spindle requirements

Create Toolpath

We use Fusion CAM to generate our design’s toolpath into a .nc code that can be recognised by the machine. For more details on how to generate toolpath using Fusion check out our personal documentations.

• Eka
• Elaine
• Tafia

CNC Controller

To control the machine we use Universal GCode Sender (UGS). A free and full featured gcode platform used for interfacing with advanced CNC controllers like GRBL , TinyG, g2core and Smoothieware.

Align X,Y,Z

We want to set the home position of the job X=0, Y=0, Z=0. You can simply move the X&Y with UGS. To determine the Z position, use a piece of paper and gradually decrease the router until the milling bit gently ‘bites’ the paper.

Airpass

Always airpass before you start your cutting job.

Cut

Run the job. If this looks fast it is because the video has been sped up 2x.

Finishing & Assembly

Take off the screws. Use a chisel and mallet to cut through the tabs. Clean the edges of the cut parts with chisel and sanding paper. Assemble. For our machine - we found that 0.6-0.7mm is the ideal range for tolerance to create ‘press fit’ joints.