hOW to cnc: a step by step guide
As a team, we custom design, fabricate, and post-process all of our CNC parts in-house. Our team was one of the first to CNC in our region, meaning we have a lot of experience with using the CNC machine and incorporating aluminum/polycarbonate in our designs. We use a ShopBot CNC Machine to cut parts, aluminum and polycarbonate as materials (1/8 inch or 1/16 inch), and OnShape to CAD our designs.
When do I use which materials?
Our team typically starts prototyping 2D custom parts using a laser cutter with either wood or acrylic. Typically, as we transition to CNCed parts, our wood parts become aluminum and our acrylic parts become polycarbonate. We'd recommend taking into account the amount of stress a part will sustain while deciding the order in which parts are upgraded. For example, a hook used to suspend the entire robot should be one of the first things changed from wood to metal, whereas a panel used to support wiring could be changed later on. Our team typically tries to transition out of acrylic for parts under any stress as fast as possible, as acrylic is delicate and tends to snap when under repeated stress.
STEP 1: CAD + ITERATIONS
Our team uses OnShape to CAD our entire robot, so typically we have wood panels already made. We then use the lighten tool in OnShape to pocket it, or remove unnecessary parts of a piece to make it as lightweight as possible. By this point, these panels should be perfect with hole placement, as iterating wood is a lot easier than iterating metal.
STEP 2: THE CNC MACHINE
We directly connect a laptop to our CNC machine and use the online programs VCarve and CNC ShopBot to translate our CAD models from design to reality with metals and polycarbonate. After importing our CAD files, we make different toolpaths for the machine, using a software called VCarve. We have one toolpath for our screw holes, another one for the pockets, and a final one of the outline. After we save each toolpath, we warm up the CNC machine using the ShopBot program. We also have to set the X / Y origin to the bottom left of the machine platform and zero out the Z axis, so the machine knows the starting coordinates of where to cut the part.
STEP 3: POST-PROCESSING & INSTALL
Finally, we begin post-processing the newly cut part! In this process, we use the dremel tool to cut the tabs of our pocketed panels. This leaves behind tiny chips, which we eventually pinch off using pliers. These chips, thin layers of metal the machine leaves in order to keep the big pockets of metal from moving around during the cut, are malleable and easy to remove. We also smooth out the outlines of the pockets using a deburring tool as the metal edges are usually rough after being cut. Lastly, we smooth out the surface of the panels using a sander and mount the post-processed parts onto our robot, creating a sturdier structure!
