Let’s say you’re trying to make something highly ergonomic like a computer mouse. You know the overall shape you want to achieve, but it’s composed of multiple parts that all have to fit together with perfect tangency on every edge. There’s an easy way and a hard, time consuming, very laborious way. Unfortunately most people intuitively use the second. If you’re thinking to yourself, “this will require a lot of lofts and guide curves” or anything along those lines, then this tech tip is for you. Prepare to save a couple hours or days of work for these types of projects.

The Goal: Make a Computer Mouse

As you can see from the image below, our model has several major components which combine to form one, smooth exterior surface. Not only will we accomplish this quickly, we will not model each part separately. Once you’ve got this concept down, you can make things like this mouse in a matter of minutes.

The basic idea of what we’re doing is that instead of modeling each part separately, and from scratch, you start with the completed model. It sounds a bit tongue in cheek, so let me clarify. We are going to begin by modeling the entire mouse (except for the mouse wheel) as a single part. The idea is that after we do this, we can whittle away at it in such a way that doing a couple of Save As operations yields several parts that all come together in an assembly to form an exact copy of the original item, but using multiple parts instead of a single part.

Step 1: Model the Entire Item

We’ve started out by modeling the entire mouse as a single, solid part. You can use any combination of tools to accomplish this. We accomplished the part below with one extrude boss, two extrude cuts, and some fillets. As you can see by comparing the picture below with the picture above, these are identical.

Step 2: Start Whittling Away

Now that we have in essence the outer surface of our mouse completed, we’ll simply start cutting away at it to generate separate parts. The first thing we’ll do is create the bottom piece of the mouse. In essence, what we want to do is to get rid of everything that is not the piece we are after. We’ll do this by creating an Extrude Cut that does this using the sketch profile below – the inside sketch defines what we’ll consider to be the bottom piece and the outer rectangle ensures that everything between the 2 sketches will be cut, which leaves just the bottom. We will reuse this outer rectangle concept in every step, so keep it in mind.

Our Sketch profile

The result of a Through All Extrude Cut

As you can see, we now have a bottom piece. Click Save As and save it as Bottom. This is the orange piece in our assembly. Obviously this is not how the “inside” of our bottom piece would look in real life – it does however contain the exterior surface we’re after, which is the whole point of this process. After we finish everything, we would need to come back into each of the parts we’re making and hollow them out and add any internal components or fastening mechanisms.

Forming the Next Part

The next step is to repeat the process. Each time you iterate this process, your starting solid should represent “everything minus the parts we already cut out”. What this means in this case is that the solid we need to start out with is everything minus the bottom piece. This is easily accomplished by editing the profile we used earlier and deleting the exterior rectangle. As you probably surmised by this point, this causes the bottom piece to be removed instead of singled out. So, edit that sketch, delete the exterior rectangle, and once the Extrude Cut feature is regenerated you will see the image below.

The sketch for our Extrude Cut

The entire model minus the Bottom piece

What we’ve just been left with is basically the entire rest of the mouse. We’ll just repeat this process over and over until we’ve gotten as many pieces as we want. Now, we’ll form the blue piece in our assembly. The left side in the image below represents what we are starting with from the step above. The right side represents our end result.

We’ll do this by sketching on the ZY plane so we’re looking directly down on the mouse, and we’ll use a profile similar to the one below. We did a Sketch Mirror operation over the green reference line to halve our work. Once the sketch is complete, we’ll use it for another Through All Extrude Cut.

The sketch for our Extrude Cut

The result – our blue piece in the assembly

Now, do a Save As. Be cognizant of always using the Save As tool when you are finished fleshing out a subcomponent because you want to be sure you don’t overwrite a previous component. Save As this piece as ButtonHolder.

Onto the Buttons

Now, just as we did before, we’re going to try to get “the rest” of the part that hasn’t been fleshed out yet. This means we’re looking for everything inside the Extrude Cut we made earlier. Similar to how we accomplished this the last time, we’re going to edit the sketch for the Extrude Cut we just made, but this time we’ll put a big rectangle around everything. Now, everything between the 2 sketches will disappear and we’ll be left with the blob of material that constitutes the buttons. Note that we very slightly modified the original sketch on the left side to split the buttons.

The sketch for an Extrude Cut

The remaining solid – the start of our yellow piece

We’ve now got the “rest” of the model. To finish out the button section, we need to make an indention for the small piece that surrounds the mouse wheel. We’ll make another Through All Extrude Sketch to accomplish this, and then we’ll Save As this part.

The sketch for an Extrude Cut

Our button piece, after some fillets.

Now, do a Save As and name this part Buttons. As you may have guessed, the next step is to make the part that surrounds the mouse scroll wheel. As you may have also guessed, this lump of material is also what we just removed with our last Extrude Cut operation. It’s time for a big rectangle.

Making the Mouse Wheel Support

Edit the sketch used by the previous Extrude Cut operation. Place a big rectangle around everything, and then exit Sketch Mode. As usual, all the material between the two sketches is removed, leaving only what we’re after.

A sketch for an Extrude Cut

The resulting solid – the beginning of our scroll wheel support

Now, we need to put a space for the mouse wheel to fit, add some fillets, etc. We’ll do some basic modeling operations and achieve the part below.

Our finished scroll wheel support.

Now, Save As this part as MiddleMouseSupport.

Putting It All Together

We’re going to skip the modeling of the mouse wheel – it doesn’t follow this process since it’s not part of the curvy out hull of the mouse. We’ve saved 4 parts now, and even though these parts all look drastically different, they share substantial portions of their feature histories with each other. In fact, as we’ve seen, many times these parts differ only by a rectangle in a sketch.

It’s time to insert these parts into an assembly. One great thing about using this method of modeling is that all of these parts share the exact same local coordinate system – what this means is basically that constraining them becomes very simple, even though they are all very curvy.

Insert each part into the assembly, and each time you do make sure your mouse is hovering directly over the origin before you click to place the new part. The reason you do this is that this aligns the origin of the part you are inserting to the assembly origin (it visually lines it up, no constraints are placed). Since all our parts share the same origin, doing this will in essence make the whole assembly line up due to the way we made these parts. The first image shows what each of our parts looks like, and the second image shows what the assembly looks like if you’ve properly inserted the parts (all your parts may be gray, just color them however you like).

Each of the pieces we’ve made

All the pieces fit together perfectly if you insert them by clicking on thec assembly origin.

If you wanted to constrain these parts together, the easiest way to do so would be to right click on each part in the Design Explorer, select Show Reference Geometry, and constrain those planes together.

Even though our assembly looks good, discerning readers know this is only the first step to the creation of this mouse. We’ve basically gotten the outside look done, but this is still a solid hunk of plastic that doesn’t have room for internal components. The next steps would involve editing each of these pieces, removing internal material that is irrelevant to the exterior look, inserting additional components and fasteners etc., but we have accomplished a task in a matter of minutes what can take an unbearable amount of time if you do it the wrong way.