We will learn how to “talk” to digital fabrication machines. CAM is how we tell a CNC machine how to interpret a CAD model.
But first, let’s take a look at the homework. How did our generative designs go? What did we make? What materials? What manufacturing process?
Typically, you start a part design in CAD. Then, you determine the manufacturing process (material, tooling, feasibility, tool paths) in CAM. Then, you set up your stock material and tooling on the CNC.
Rarely does the process go in one straight line:
CAD –> CAM –> CNC
Hopefully, we are pretty familiar with CAD (Computer Aided Design) at this point. So on to the next step.
Computer Aided Manufacturing (CAM) is the use of software and computer-controlled machinery to automate a manufacturing process. -via
CAM is the stage where you decide how the part is going to be made — Will it be 3D printed? Will a CNC router cut the part? If a router, what brand and model of router? What type of end mill will you use? What size? What shape?
CAM is the stage where you decide what the stock material is going to be — wood, aluminum, cork, …
CAM is the stage where you decide the path the tool (the end mill) is going to take. Is the toolpath an efficient path.
Fusion 360 has the functionality to CAM a part. This is pretty incredible for free software and we will explore this functionality in full next week.
Next step. CNC (Computer Numerical Control) is the automated control of machining tools (such as drills, lathes, mills and 3D printers) by means of a computer. –via
We won’t actually be making a physical part on a CNC machine for this class, but we will give you the tools to get started if you choose to physically make something down the road.
For our discussion today we will focus on using a 3 axis CNC router, sometimes called a CNC mill or even just a CNC. More specifically, we will be talking about the Bantam Tools PCB Milling Machine. We have a few of these machines on the floor. They are relatively safe and user friendly.
The CNC is connected to a computer that is running software that can can interpret CAD/CAM and tell the CNC how and where to move.
Stock material is mounted to the work bed. For the Bantam, we use double sided tape to fix it to the spoilboard. The spoilboard is the work surface that you can mill into, jut a little bit.
A bit, or end mill, is mounted to the spindle (the spinning part). The bit is lowered slowly till it comes in contact with the stock material. And material is removed.
2.5D vs 3D
Working in two and a half dimensions (2.5D) means you are cutting a part that has multiple flat features at varying depths. … Most simple CAM programs deal with 2.5D parts. Working in three dimensions (3D) means that you have the ability to control at least three axes simultaneously. -via
2.5D parts are easier to design and fabricate, cheaper too. They are also much easier to CAM. For our examples today we will only consider 2.5D parts.
There are no undercuts in a 3 axis CNC’d part. Undercuts are material removed from under the top surface. No over hangs, no double sided parts.
Also known as tooling, the end mills are the sharp cutting bits that remove material from the stock.
Step Down and Step Over
The depth an end mill cuts down for each pass is dependent on the type of stock material. This is know as step down. Soft materials can have an aggressive step down, harder materials have a smaller step down.
Step over is how far from the previous cut the next cut occurs.
Feeds and Speeds
The speed the bit travels through the material while cutting and the RPMs of the spindle (spindle speed) are unique for the material you are cutting. These are known as the feeds and speeds.
Bits come in numerous profile styles and sizes. The size and profile determines the type of cut that can be made.
2.5D parts are typically made with flat bits, true 3D shapes are made with round or ball end mills.
The end mills are attached using a collet and collet nut
The path through space that the tip of a cutting tool follows on its way to producing the desired geometry of the workpiece. -via
G-code, code telling the machine tool what type of action to perform. -via
G-code is the language that CNC machines speak. CAM programs spit out g-code which is then loaded into the CNC machine.
Much like our first week of Psuedo CAD, we will do the same with CAM. Let’s talk it through before we actually do anything.
What are we cutting? 2.5D part, what kind of processes? Pockets? Holes? Cutouts?
What kind of CNC machine?
What kind of stock material? What are the dimensions of the stock?
How is the stock mounted to the CNC machine?
What kind of end mill are we using?
What are the toolpaths of the operations?
Sneak Peak of Next Week
We are in week 10, time to start thinking about your final project. Your project can be based on one or many of the techniques we have covered in the class so far. I want you create a project proposal: hand-sketches, gathered inspiration, etc and document it on your blog.