3D Printering: Making A Thing In AutoCAD, Part II

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It’s time once again for another part in 3D Printering’s series of Making A Thing. Last week was a short tutorial on the beginnings of making a thing in AutoCAD. This is an extremely complex software package, and in a desire to make things short and sweet, I broke this AutoCAD tutorial into two parts.

Since we already covered the 2D design portion of AutoCAD, part II of this tutorial is going to turn our 2D part into a three-dimensional object. Check out the rest of the tutorial below.

Our Thing

Just like all of these Making a Thing tutorials, we’re using this object pulled out of a nearly 100-year-old textbook on drawing and drafting. We already have a 2D projection of this part, from the previous AutoCAD tutorial, so let’s just dig right in.

Views and Presspull

In the last installment of this AutoCAD tutorial, we only used the ‘top’ projection. This is great if you’re working in 2D, but making a 3D object is nearly impossible. The first thing we need to do is change to an isometric projection in AutoCAD. To do this, just click on the ‘view’ tab and change the view to SE Isometric. You’ll end up with something that looks like the picture to the left.

With being able to see the Z axis sorted out, the first order of business is making a 2D object 3D. You might think the command we want to use here is extrude. You’d be terribly wrong, though. The command we want to use is called presspull.

Extrude is an AutoCAD command that pulls the highlighted objects (in our case, the lines making up our part) through the Z axis. It doesn’t make your lines a solid, though, so unless you’re designing single-thickness vases to print on your RepRap, there isn’t much use for extrude.

By selecting the presspull command from the ‘solid’ menu in AutoCAD, we can click on the object we want to pull up into the Z axis and make them solid. If you’re following along with this tutorial by copying all these steps, highlight the main part of our ‘thing’, type in presspull, and type in the height you want to pull it up to. In our case, we want this part of our ‘thing’ to be 7/16″ thick, or 0.4375 in decimal inches.

Editing Solids

You’ll notice our ‘thing’ is missing something – the flange on top with the drilled hole. Not to worry, because by playing with the box and cylinder solids we can add that part in. Here’s our process in handy animated .gif format, complete with a textual description of how to do it.

Switch to the NE Isometric view. From the Home tab, select box. This is a tool that allows us to draw a box in three dimensions, by selecting two points on the X and Y axes, and extruding it up through the Z axis.

From the 100-year-old drawing we’re working off of, the top of our box should be 7/16″ tall for the base, then another 7/8″ tall to get to the midpoint of the cylinder we’re going to put on. That adds up to 1.3125 decimal inches, so click one corner of our 2D box, click the opposite corner, and type in 1.3125.

Now we have a bit of a challenge. We need to add the ‘dome’ on our part. This is easily made with the cylinder tool, but we need to make sure it’s aligned on the center of the edge of the box we just made. If you’re following along with this tutorial, you’ve already experienced some of the ‘snap-to’ effects, but nothing that’s a midpoint yet.

OSNAP. Yep, the command you want to type in is called osnap. That joke gets really, really old after the first week of a drafting class, by the way.

Osnap enables different snap-tos, allowing you to draw something from the midpoint, endpoint, and center. By default midpoint isn’t selected. Click that check box and get hit OK. Draw your cylinder, then from the solid tab, click Union, select both the box and the cylinder and hit enter.

We’re nearly done here. All that’s left to do are the drilled hole through this flange we just created and the counter bore. First we’ll work on the drill that’s 7/16″ in diameter. Not radius, diameter.

Using your new-found osnap skills, draw a cylinder that is 0.21875 decimal inches in diameter. Pull that through our flange and subtract it, just like we unionized the box and cylinder above. The counter bore is left as an exercise to the reader because It’s the exact same process.

Wrapping things up

Since our goal is to design a part for a 3D printer, we’ll need to make an STL file. This is done with the export command. It’s a simple process, but there is one catch: you must select all the objects in a part before saving. Right now, our ‘thing’ is made of two parts – the weird circle thing with a slot, and the dome thing with a hole and counter bore. We could export both these parts together, but that’s rather inelegant. Select Union, click both parts, and hit enter. Then export to .STL.

Will you look at that. We made a thing. You also just learned AutoCAD and the Escape key on your keyboard is crying.

Compared to the previous tutorial of making a thing with OpenSCAD, designing a 3D printable object with AutoCAD isn’t more difficult, it’s just different. Next week, sometime after Christmas, we’ll check out some more 3D design software and make our ‘thing’ once again. If you have any suggestions on what software I should feature, drop a note in the comments. I lost the Post-It that had all the softwares I was planning to use.

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