In this video of the Zero to Maker series, we are diving into CNC machining, a manufacturing process that makes parts by cutting away material with a milling bit. This process fills a gap that 3D printers and laser cutters can't fill by allowing you to cut thick materials, soft metals, and very large parts. CNC machining has a reputation for being a little daunting, but in this video, we take a look at making a giant molecule kit with a CNC machine and demonstrate that it can be quite an easy process.


In this chapter of the Zero2Maker Workshop, we're going to be covering CNC machining, a manufacturing tool that can make really large parts and even metal parts. If you're new to this workshop, Liam and myself will be taking you on a fast-paced and practical journey to learn a wide variety of maker skills so that you have the tools and knowledge to make anything. Follow along as we develop our own projects and share insights into the process.

This week as a part of Fab Academy, we were tasked with making something big with a CNC machine. Now, unfortunately, the robot project that I'm building doesn't actually need any CNC parts, so we aren't continuing that this week. Instead, we're going to do a quick little project and make this giant molecule kit.

So CNC machines are kind of similar to 3D printers and laser cutters in that they consist of a system of rails and motors called a gantry that moves around a head with a tool on it. For a 3D printer, this tool is a hot end that melts and extrudes out plastic to build the part. A laser cutter is, well, a laser that blasts away and cuts materials. A CNC machine typically has something like a router with a milling bit that cuts away material.

A CNC machine is kind of the opposite of a 3D printer. With a 3D printer, we add the stuff we need bit by bit, but with a CNC machine, we start with all the material and then subtract or cut away what we don't need bit by bit. And there are advantages to using a CNC over something like a printer or a laser cutter. With 3D printing, you're typically limited to making things out of plastics because it can only use materials that it can melt down and push out of a nozzle. Laser cutters are restricted to what lasers can cut, so anything reflective like metal can't be cut, nor anything too thick. But a CNC machine, thanks to that really high-powered milling bit, can absolutely blast through wood, plastic, and metals a lot of the time. Metals are a bit harder to cut and might really push a machine, but chances are you'll be able to cut something soft like aluminium.

CNC machines can come in small desktop formats, but they also tend to come in much larger sizes. The one we used could cut parts up to one and a half by one and a half metres. I'm a little bit over six foot, but I could cut an outline of myself on one piece of wood if I tried. So you can CNC pretty big things, and we actually saw many other Fab Academy students making furniture pieces this week. That's actually what Liam did. He made this small coffee table. And they can cut things at these scales pretty quickly. Liam's table only took about 20, maybe 25 minutes to cut. Printing something this big would take days. And although they are big and fast, they are still precise machines. Just like laser cutters and printers, you can cut complex shapes with very tight and accurate dimensions. But there are, of course, downsides to them. The first is that because it makes all of its cuts with a round milling bit, it can't make sharp corners on the inside of a part. We'll talk a little bit more about this later and how to design for it, but it's kind of like trying to draw a perfect square with a big round marker. The edges aren't going to be sharp. Another thing is that CNC machines are much harder to come by. There is kind of a scale with 3D printers on one end being everywhere and highly accessible, laser cutters a little bit less so, and CNC machines much rarer and harder to access. Small-format desktop CNC machines are becoming more affordable and feasible for home shops, but a good bet would be a FabLab. Some makerspaces might have them, but it's a better bet that you'll find one at a FabLab.

CNC machines are also a bit harder to use software-wise. They do follow the same general workflow as 3D printers and laser cutters, though, in that you design something in CAD and then you go through a process and turn it into machine code or instructions. In CNC routing, we need to use a CAM software for this process, computer-aided manufacturing. It's similar to how we need to use a slicer when 3D printing something, and a slicer is actually a CAM software as well. We just call it slicer when we're referring to printing. This slicing step in 3D printing is super easy. Import your model, select your printer and material, maybe change the layer height and infill if you want, and then hit export. Super easy. But with a CNC machine, it's a lot more involved, and there is a lot of micromanaging everything in that process. Now, I don't want to dissuade you from CNCing anything. They are an incredibly powerful tool, and if you go to a makerspace or FabLab, chances are they'll be able to help you with this process, so it won't be so difficult. But we're just going to quickly run through this process to take a look at some of the important concepts around CNC machining.

Ah, but we encounter yet another issue here. Software compatibility. A CNC machine might only have support for a specific CAMing software. For our machine that we used at the FabLab, we have to use Fusion 360. The machine at the makerspace down the road from you, though, might need a very niche and completely different software. And there can be wild differences in how to use these softwares, but we're still going to quickly run through our process for our machine in Fusion 360, because although the workflows might be different, there are still ideas and settings that are fairly universal.

First things first, we need a CAD model. Now, we're going to be making a larger version of this molecule kit that I made in the laser cutting week, and it's already been modelled in on shape like so. But the first problem is that it needs to be a model in Fusion 360. So I've gone ahead and I've remodeled all of this in Fusion like so. What might have been smarter would have been to export it as a step file like so. And then we can import this into Fusion like so. And a step file is kind of a universally accepted CAD file. It's not a 3D model like an STL, but a model defined by math like a CAD software uses. The only issue is that when you export something as a step file and then import it back into CAD, you lose the history tree and you can't go back and make any changes. But you can edit it from this point onwards like we can do here. We can extrude it up and we can just keep working on it from this point here.And that's all we need from the modeling phase. My workflow calls for a 3D model like this, but yours might call for a vector. So always check what your process needs.

Then I went ahead and duplicated as many parts as I needed and then arranged them to fit on the stock that we were using. A stock is just a technical name for the material that you're cutting. Our stock is just going to be 12 millimetre plywood. We can create a new milling cut and then we can also set up the stock that we'll be cutting. This is just a virtual representation of it. We also have to set where we want the home position to be relative to that stock.

Now that we've got our virtual stock and the parts we want to cut out of that, we need to tell CAM how to actually make the cuts to cut our parts out of that. We can go up to and create a new 2D contour cut. In here, we can select, very importantly, the bit that we're going to be using to make this cut, as well as we can set all of our speeds here, like the RPM speed. This is not only how fast the mill bit is going to be spinning, but also how quickly it's going to move through the piece when it makes these cuts. We need to select what features we're actually going to be making our cuts along. Obviously, we want to cut down to these bottom surfaces here, like so. We can also choose to generate these things called tabs. Tabs are very important. Once your part has been cut away from the stop, there's nothing stopping it from moving around and it might accidentally fall out or might get caught up in the milling bit and damage the part or the machine. We can generate these tiny little tabs here in our CAM software. These are designed to be little pieces that are left behind and hold your place in peace. We can just come along later and cut all of these off.

The CNC machine is going to cut away your part bit by bit, and we can choose how much material it's going to remove in each pass that it makes. Here we could change it to one millimeter, and this is going to make a lot of passes and take a while, but it's going to be a lot cleaner. But we're just going to speed up this process and make it five millimetres. That means it's going to be a bit quicker, but it's going to have a little bit rougher surfaces that we might need to clean up. This is also going to put more stress on the milling bit, and you need to just make sure you're not pushing it too hard as to not break it. But this bit can handle up to 12 millimetres in a pass of plywood, so five millimetres is not really going to be an issue.

Now that's all I need to do for this project, but if I wanted to have some more cuts, maybe a slower and smoother final finishing pass that gives it a nice and clean surface, or maybe I wanted to cut out some pocket features, I would need to go through that whole process again. This is one of the annoyances of CAM software. It doesn't automatically figure out how to make your part like it does with a 3D printer and slicing. There might be smart CAM software out there that does it for you, but chances are you will need to manually set up and specify every different cut you want to make. For us though, it was pretty straightforward, and it's not too hard when you treat it almost like a giant laser cutter, like we're doing so here. It's worth keeping in mind that you can cut things like a pocket here, which is where you cut into the material, but not all the way through. Or you can also make three-dimensional carvings, but there is a bit more complexity in that. But for now though, we are done, and we can see this cool little simulation here of how the machine's actually going to go through and make the passes to cut it, and we can just use it to make sure everything looks all right. From here, we can go into post-process or just export our thing, and then we can export our machine code out.

Now that we have our machine code, we need to get it on the CNC machine. Usually there'll be a computer plugged into it, which controls the machine with a sender software, which takes the machine code commands we just made and sends it to the machine to make your parts. We clamp down our stock nice and tight to the bed, and then we zeroed the mill into the corner of the plywood. This is where we align the machine to the virtual home point that we set in Fusion 360, so it knows where that plywood is on its cutting surface. All in all, it took about 45 minutes to cut two lots of these from some very large sheets of plywood. That was our entire process. Yours might be different. You may not even need to do the process of camming, and you might be able to just hand in your CAD files and get them cut. Regardless of what you need to do, it's not that difficult of a process. It's just a little bit more involved than what you might be used to in something like slicing a model for 3D printing.

Now let's have a quick talk about design for CNC machining. Thankfully, there aren't as many design rules and considerations as something like 3D printing. That is just kind of one really big thing to watch out for. The main thing to design for with CNC parts is when you need to make internal cuts with sharp corners like this square here. Because we're going to cut a square hole with a round bit, we're going to be left with these little kind of corners here where the milling bit can't get right into that sharp edge. There's a few things we can do about this. But first things first, does it matter? Does it actually matter that it's not a perfect square like so? Most of the time is, yes, it does matter. If you can have rounded corners, then let them be rounded corners. In most of the other examples when you're actually going to need it to be accurate, there are a few things we can do. On my molecule kit, I took a really, really lazy solution because these two slots here is where it's going to come together and join to create our little ball thing. The rounded corner is going to prevent them from fully slotting together. So all I did was I went to this edge here and I just simply extruded it backwards a little bit like so. Half the diameter of the milling bit I'm using. Because that square edge is a little bit back, when it makes those rounded corners, it's going to be able to fit together nicely.There is a much nicer solution to this. So here I've got the sketch for our part and I'm just going to go ahead and create these little semicircles here. And these are just the size of our milling bit. I'm just going to go along and quickly make them on all the edges like so. So now that we have these little semicircles on the corners of our cuts, this is going to give room for the milling bit to get in there and give us our nice and sharp corners. This is going to remove more material than we might have wished for, and it is going to make it maybe look a little bit less nice than what we might like. But it is going to give us a square hole in there that we can use. And you might see a lot of different ways to do this, and for different situations there might be better or worse solutions, but this is one of the best I've come across.

Another thing to keep in mind is to avoid making impossible geometries, like this internal geometry here that we can reveal with a sectional view like so. This bent hole running through the middle of our part may be possible for a 3D printer to make, but it's not possible to cut with a straight milling bit on a CNC machine unless you've got a really fancy 5th axis CNC. And as always, whenever you're making anything, ensure that you allow for proper tolerances. These two pieces here slot together and they're 12mm thick plywood. So in my CAD model, if I made these slots only 12mm wide, they're not going to fit together. They need to be a little bit thicker. I made mine about 0.2mm wider, so this gap is 12.2mm, and they fit together really snugly. Probably a little bit too tight, so I might go with 12.25mm. But 0.2mm to 0.3mm for things that are going to slot together and for things to fit inside of each other is a really good bet.

So after all that design, camming and machining, we finally have our final CNC'd pieces. I had some issues with one of my runs. It left behind this really thin layer of wood. It was paper, paper thin, but obviously it didn't take much to remove it. And we cut our pieces pretty quickly with some rough cuts, so we have some really rough edges on the bottom here, but a quick hit of sandpaper and they cleaned up really nicely. And once all my pieces were ready, everything just slot together really well. And just a little bit of malleting and it'll fit together to make our molecule of ethane. And after a few coats of paint, I think it came together pretty darn well. But it's so big that we don't even know where to put it. It's about 1.4m in width, so yeah.

Well, I hope you enjoyed that little dive into CNC machining. I know we did with our Fab Academy projects and I definitely have some big project ideas that will need a CNC machine. Maybe some nice machined aluminium parts or using that really large build volume to make some panels for a full-sized arcade cabinet. And I hope you've had some great ideas of things that you could build as well. Till next time.



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