Sketching in AutoDesk Inventor

This is just one hub in a series of 15 hubs on using AutoDesk Inventor for 3D modeling. The index hub is here.

I don't know about you, but whenever I get a good idea, a sketch or a note is the first thing that happens. Same thing in Inventor. To make any part, a sketch is the best way to start. Inventor lets you draw a section of a part in 2D, then extrude, revolve, or sweep it later. The coolest part about sketching in Inventor is that you can add lots of detail in a sketch, and you don't need to worry about moving around in 3D. When you extrude it, all that detail shows up and makes the part look great. It's kind of like painting - if you ask a painter, the prep work, like cleaning and sanding, is the best way to guarantee good quality.

In this tutorial, you'll learn how to use the sketching commands in Inventor, like line, box, trim, fillet, and offset. Using just these basic tools, you can draw just about anything. When you're done, move on to the next tutorial to make it 3D!

By now, I assume you've learned how to get into sketch mode. We'll start out there, in the screen shown in Picture 1. I've decided to draw a fictitious part for this tutorial, so if anything looks odd or unconventional, it's because I have no idea what I'm drawing.

Rectangle Command

We'll start by drawing a box. Click on the "Rectangle" command - it's one of the smaller buttons in the upper left corner, assuming you are in the sketch tab. Since I want this part to be centered on the origin (where the x and y coordinates are equal to zero) I'm gong to pick a size that lets me do this. I want my box to start out at the coordinate x = -2, y = -1. To do this, assuming you have just clicked "Rectangle," hover near the spot and push the "Tab" key on your keyboard. You'll notice that the x coordinate next to your cursor is highlight. This means you can change it, so type in -2. Then push tab again, and type in -1 for the y coordinate. Notice that there are now two lock symbols on the coordinates, as shown in Picture 2. This means that your point is fixed right there, and won't move. Click to start your rectangle.

Now Inventor is asking you for the opposite corner of your rectangle. Using the same method, enter x = 2, y = 1. Voila! You have a rectangle.

Dimension Command

If you wanted to change the dimensions of the box, you would need to click on the "Dimension" in the "Constrain" section at the top of the screen. Then you would have to click on the dimension and enter a new one, just like Picture 3 shows.

Fillet Command

I don't know about you, but I like it when my parts have rounded corners instead of impossibly sharp edges. So I like to add fillets to my parts to make them look smoother. It also lets light reflect off of it in better ways, but we won't worry about that until we get to the hub about exporting images of our product. So, to start a fillet, click on the "Fillet" command in the top left of the screen, on the third row of buttons after "Line." You should see a menu pop up, just like the one in Picture 4. Enter the radius of the fillet you want to create, and then click the two lines that form your corner. It's important to note that the lines do not have to be touching. In fact, they can be parallel like they are in Picture 5 (but then it ignores the radius you entered). An interesting application of this is to set the fillet radius at zero and click on two lines that do not intersect, but aren't parallel. Inventor will extend those two lines until they meet.

Line Command

After adding two fillets to the front of the rectangle, we'll add a more complicated feature. This time, we'll use lines. Start off by clicking "Line" in the upper left of the screen. Then hover over the center of the bottom of the rectangle until your cursor "snaps" to the y axis and the line. Snapping is very handy, and lets us make parts that are perfectly connected, instead of one or two thousands of an inch off. Now move your mouse up a little, and type in "1" into the y coordinate box, making sure the line "snaps" to the vertical axis. See Picture 6 for an example. Press enter, and you should have a line exactly one inch ling and perfectly straight. Repeat the process, this time to the left for one inch. Note that Inventor automatically adds another line, so you don't have to start one again.

Now we want our line to come back down and to the right at a 45 degree angle. But this time, we're going to snap it to a 45 degree and, and also snap to a distance. Hover over the midpoint of the first line for a moment, then slowly move your mouse back the the left, until the angle reads 45 degrees. At the same time, the line should snap to the midpoint of the second line, and you should see something like Picture 7. Click.

Once there, finish the shape by clicking on the rectangle just below that point. Inventor will now stop adding automatic lines every time you click because it knows that you have closed a shape. Repeat this shape on the other side (or if you're feeling courageous, mirror it using the process shown a little further down).

Trim Command

You might have noticed that the shape looks like a dovetail groove. In fact, that's kind of what I meant it to be. My unknown part is starting to get a bit of meaning now. The problem is that there are too many lines. The first line you drew was just a test line, to measure distance. Go ahead and delete it. Now we see that the bottom of the rectangle is in the way as well, if we want this groove to be open. But we can't delete that one, since doing so would take away the whole line. This is where we use trim.

Click on "Trim." It's a little more to the right than all the other tools, because it's in the "Modify" panel. Hover over the section of the line you want to remove and make sure the dotted line that appears only covers the section you want to delete. Then click. Picture 8 shows this process. Make sure you don't need to trim or delete any more lines, and we'll move on to mirroring.

Mirror Command

I'll readily admit that I just decided to change my part so I had an excuse to show you how to mirror. But, after all, that's what it's all about, so don't look at me funny when this part starts to look like some kind of misguided hatchet.

To start mirroring, click on the "Mirror" button under the "Pattern" section. You may or may not see the actual text, since the ribbon likes to resize itself, but the button looks like a mirrored number "1." Picture 9 shows the menu that pops up.

Ok, this is important. Not because mirror is extraordinarily important, but because this process is used over and over and over again in Inventor. Do you see the two arrow buttons? They should both be red right now. If you see this, if means you need to select something for the function described next to it. In this case, the left side arrow asks you to "Select." It wants the parts that you are going to mirror. If you aren't sure what it wants, click on the button and look in the lower left corner. For this button, it says "Select geometry to mirror," just like you can see in Picture 9.

So go ahead and select the entire part. Notice that the arrow turns white - this tells you that you are all set for that arrow (unless you want to select more). Now click on the second arrow. This one wants you to select the mirror line, or what line the parts will be mirrored over. Select the top line of the rectangle and then click apply. Done.

Selection and Delete

Now we want to delete the line that goes right through the middle. Click on it (or them, since you mirrored them) and push delete. You an also click and drag from the right to the left for a crossing window (anything it crosses is selected) or from the left to the right to select anything that is entirely inside the box. Then, of course, push delete. See the final part in Picture 10.

Stretch Command

I didn't plan on having the part this big, so we're going to stretch it down by a half inch. Click the "Stretch" button and use the same process as above (see, I told you it was important) to select the upper half of the part, then the "Base Point." The base point is the point you use to drag the part, and it makes a difference if you want to snap it to a particular spot. In this case, we don't, so click anywhere on the drawing and move it slowly down. Inventor should show you dark lines for anything that is moving, and dashed green lines for the old position, like those shown in Picture 11. I moved the top down until the dimension on the right said 1.5 inches instead of two, then clicked.

Offset Command

Since this is started to look like a modular shelving system to me, with that dovetail groove for shelves to latch into and slide up and down on, I'm going to think about manufacturing it. In that case, I probably don't want a solid piece of aluminum - I'll just want an outline of the shape, with the inside hollow to save weight. To do this, I'll use offset.

Click on the "Offset" button, just underneath "Stretch," and move your mouse back to the part. You'll see that a new shape, similar to the drawing, is following your mouse. Click where you think the thickness is about right. See Picture 12 for an example.

Congratulations! You're done with the sketch! Click "Finish Sketch" in the upper right corner to return to part mode. You should now see something like Picture 13. Extruding is up next.