Download 123D DesignCAD programs have a reputation for being expensive, clumsy and hard to learn. Autodesk’s 123D Design changes all that, with a desktop application that’s fast, easy to learn – and free. We’re going to build a simple project to demonstrate the basics of the software’s tool set.
Once you’ve downloaded the software, open it up and you’ll see a floating window with all the tool and menu elements incorporated within it. It doesn’t run as a standard app on any platform, but that means it looks the same on a Mac or a PC.
1. Take your measurements
Here in London I still get milk delivered by a real milkman (and yes, he even whistles a jolly tune). The glass bottles are capped with a foil lid, but once opened the lid no longer seals the bottle – especially in transit. So I decided to design a 3D-printed replacement lid. The first step was to measure the bottle top, which showed it to have an external diameter of 35.5mm and an internal opening of 27mm.
Even if you’re used to working in inches, you should consider switching to metric for 3D printing. It’s more accurate, and more compatible with design and measurement software.
2. Choose your tools
The toolbar at the top contains all the tools you’ll need to get designing. The first icon is for so-calledPrimitives – cubes, spheres, and so on. Click on this, then choose the Cylinder from the pop-up choice beneath:
Click the tool on the ground plane in the artwork window, and drag to set the size. As you do so, you’ll see a pop-up showing the radius and height. You can also type numbers in here to set precise measurements, which is more accurate than simply dragging the cylinder.
Our milk bottle has an outside diameter of 35.5mm, so let’s give the cap a diameter of 40mm to allow for the thickness of the filament. That means a radius of 20mm, so type in that figure.
As for the height, that’s really a matter of comfort; I reckoned 15mm – a little over half an inch – would be deep enough to provide enough of a surface to be able to twist it on and off easily.
4. Make the opening
To make the lid hollow, we need to use a different tool. The second batch of toolbar icons is the Sketch set, so use this to select the Circle tool:
5. Set the size
The size of the bottle itself is 35.5mm, so let’s make the opening 36mm in order to give it enough clearance to slip on and off easily.
A diameter of 36mm means a radius of 18mm, so we can set that numerically just by typing the figure into the box.
6. Choose to extrude
When you select any object by clicking on it, a tiny gear appears next to it. Clicking on this gear pops out a range of tools that can be applied to the object. The third one along is Extrude, so select this to begin the extrusion process:
After choosing to extrude the shape, an arrow appears on the object which we drag to set the depth of the extrusion.
We’d normally think of extrusion as a process by which a shape is given extra height, and that’s certainly a common use for it. But if we drag the arrow down rather than up, we’re able to sink it into the cylinder, so creating a void inside.
We made the cap 15mm high, so let’s set the depth of this hole to 13mm. That will leave a 2mm thick base, which will both be enough to print on and enough to make a solid lid for the finished cap.
8. Add a ring
The cap will be a slightly loose fit. Have a look at the shape of the bottle neck, and you’ll see there’s an indentation just below the top: this is where the original foil cap wrapped under to seal it. We can create a ring that will fit into this indentation, holding the lid firmly in place.
To start, go to the Primitives section on the toolbar, and choose the Torus object:
When you add a new object to an existing one, you’ll be able to choose where to attach it. Clicking on the interior of the base will position the torus there.
We only want a very thin ring – a diameter of 2mm will be plenty. That means a radius of 1mm, so we can type that in.
123D Design also gives us the opportunity to set the Center Radius, which sets how large the ring is. The opening is 18mm, so if we set the radius to the same figure, the ring will project 1mm into the cap – the Center Radius, as its name implies, is through the middle of the torus.
When we now try to select the cylinder, we find we can’t hit it – because the circle we drew to make the hole is in the way. Even though it’s now the lid of a hole, 123D Design still sees it as being an object we’ve created.
The simple solution is to select it, and hit the Backspace key to delete it. It’s done its job, and we don’t need it any more: the hole it created will still be there.
11. Move the ring
When we created the ring, we made it right at the bottom, lying on the inside of the cap (the cap is, of course, upside down). We need to move it so it will snap under that rim on the bottle, which is 5mm down from the top.
It’s hard to see exactly what we’re doing from this angle, so let’s change the viewpoint. On the far right, you’ll see a cube with writing on it. This shows the current view. You can change to the Front, Left and Top simply by clicking on that face; or you can view from an edge or a corner, by clicking on it – it will highlight when you roll over it. Try clicking on different sections to see how the view changes: you can always click the Home icon to return to the initial viewpoint.
We’re clicking on the Front, so we can view the cap head-on. Clicking the Gear icon allows us to select the Move option for the torus; let’s drag it up by 5mm so it’s exactly in the right place:
Adding a plug that fits on the inside of the bottle will provide an additional seal, preventing the milk from spilling out when the bottle is tilted or in transport. We can start to create this as a simple cylinder, with a radius of 13mm. This gives a diameter of 26mm, which is small enough to fit comfortably within the 27mm opening on the bottle.
13. Round the edges
Once the interior plug has been placed, all the elements of the cap have been included in the final design. But we can make the cap more aesthetically pleasing, as well as more comfortable to hold, by rounding off those hard corners.
Rounding edges and corners is called filleting (as opposed to chamfering, which means slicing off the edges at a sharp angle). To begin, select the upper edge of the interior plug by clicking on it – it will highlight in blue – and then, from the Modify menu, choose Fillet. You can also click the Gear icon to select the Fillet option if you prefer:
14. Drag to round
You can now drag on the arrow, and as you do so you’ll see how the hard edge is pleasingly rounded. If you prefer, you can type in a rounding radius instead. On the plug, I used a radius of 4mm to get a large, smooth edge.
You can apply the Fillet operation to several edges at once. So if you click on the interior and exterior edges of the top of the lid, as well as on the base, you’ll find you can round them all together. Here, I’ve applied a rounding of just 1mm.
15. Save the file
Clicking on the 123D Design logo in the upper left corner will pop open a menu that allows you to Save your work. At the bottom of the menu is the Export button, and this brings up a dialog that allows export in several different formats. Choose STL as the file type, and you’ll have a printable file to work with.
Creating the virtual model is all very well, but how does it work when it’s printed? There’s only one way to find out.
It took about 25 minutes to print this cap, and when it was finished it fit neatly onto the bottle top. This is one of the big advantages of using a digital micrometer to take initial measurements: the more accurate they are, the more likely it is that the finished product will work.
The spill test was another matter. Would the model itself be watertight (or, in this case, milk tight)? Would the cap fit snugly enough to prevent leakage? Again, experiment is the only way to find out:
Lance Atkins shares this great video tutorial on breaking down how the lofting feature works in 123D Design and how to use it.