CAD basics with Tinkercad

Up to now you have been a printer of other people's ideas. In Chapter 6 you grabbed ready-made designs, dropped them into the slicer, and watched them appear in plastic. That is a great way to start, and honestly you could stop there and still get years of use out of your printer. But there is a line you have not crossed yet, and crossing it changes everything: making the shape yourself.

That is what this chapter is about. We are going to design a real object from nothing, on screen, and you are going to do it with a free tool that runs in your web browser.

What CAD actually means

CAD stands for Computer-Aided Design. Strip away the acronym and it just means using a program to draw a three-dimensional object: a digital model of a thing that does not exist yet.

Here is where it fits in the journey. A printer cannot print an idea in your head. It needs a 3D model, a file that describes the exact shape: how wide, how tall, where the holes are, how thick the walls are. CAD is how you make that model. Once you have it, you hand it to the slicer (the program from Chapter 5) which chops the model into layers and writes the instructions the printer follows.

So the full chain looks like this:

your idea  ->  CAD (you draw the model)  ->  slicer (makes layers)  ->  printer (makes plastic)

The middle step, CAD, is the one you have been skipping by downloading designs. This chapter fills it in.

Don't be confused. A CAD model and a sliced file are not the same thing, and they do different jobs. The CAD model describes the shape of the object: a cup is this wide, this tall, hollow in the middle. It says nothing about how to print it. The slicer takes that shape and produces machine instructions: heat to this temperature, move here, squeeze out plastic, drop down one layer. CAD answers "what is the object?" The slicer answers "how does the printer build it?" You always do CAD first, then slicing. You can reslice the same CAD model a hundred times with different settings without ever redrawing it.

Why Tinkercad to start

There are many CAD programs, and some of them are intimidating walls of buttons. We are going to use Tinkercad because it was built for exactly your situation: a complete beginner who wants results today.

A few reasons it fits:

  • It is free.
  • It runs in a web browser, so there is nothing to install. You make an account and start.
  • It works by dragging simple blocks (boxes, cylinders, spheres) onto a surface and combining them. There is no intimidating math and no hidden menus to memorize. You build the way you might stack toy bricks.

Tinkercad will not be the last tool you ever use, and that is fine. When you outgrow it, the usual next steps are FreeCAD (free, very capable, a steeper learning curve), Autodesk Fusion (free for hobby use, professional-grade), and Onshape (also browser-based and professional). There is also OpenSCAD, which is a different beast entirely: you design by writing code instead of dragging shapes, and we cover it in Chapter 10. For now, Tinkercad gets you moving with the least friction.

A note before we start: exact button names and menu wording in web tools change over time, so I am going to describe what you do rather than quote labels that might have shifted since this was written. The ideas below are stable even when the buttons move.

The core ideas, one at a time

Open Tinkercad in your browser, make a free account, and create a new design. You will land in a 3D workspace. Let me walk you through the pieces.

The workplane

The flat surface you see is the workplane. Think of it as the ground, or the printer's build plate seen from inside the computer. Everything you build sits on or above it. When you eventually print, whatever is touching the workplane is roughly what touches the real build plate.

Moving the camera around

You are looking at a 3D scene, so you need to be able to look at it from different angles. Three motions:

  • Orbit: spin the view around your object to see it from the side, the top, the back. This is usually done by holding the right mouse button (or a two-finger drag on a trackpad) and moving.
  • Pan: slide the whole view left, right, up, or down without rotating.
  • Zoom: the scroll wheel moves you closer or farther.

Spend a minute just orbiting around the empty workplane. Getting comfortable looking at your object from every side is half the battle in CAD, because a shape that looks fine from the front can be completely wrong from underneath.

Dragging in a shape and sizing it

Off to one side there is a panel of basic shapes: a box, a cylinder, a sphere, a cone, and more. Drag a box onto the workplane and drop it. You now have your first object.

Select it (click it once) and you will see small handles appear: little squares and points around the shape. Drag a handle and the box stretches. That is the quick, sloppy way to resize.

Here is the part that matters more than anything else for a useful object: type exact numbers. When a shape is selected, Tinkercad shows its dimensions, and you can click a dimension and type a precise value in millimeters. Make that box 40 mm wide, 40 mm deep, 10 mm tall by typing, not by eyeballing the handles.

Why so insistent? Because 3D printing is a real-world, physical thing. If your phone stand is supposed to cradle a phone that is 75 mm wide, the slot has to actually be a hair over 75 mm. "Looks about right" produces parts that do not fit. Drag to rough it out if you like, then type the real numbers. Millimeters are the universal unit here, the same unit the slicer and printer use, so you never have to convert anything.

Moving and lifting

To move a shape along the ground, click and drag it across the workplane. That slides it in X and Y (left/right and forward/back). As you drag, it snaps to an invisible grid, which keeps things lining up neatly. The grid spacing is adjustable, but the default is fine to start.

Lifting a shape up, off the ground, is a separate move. Z is the up/down axis (the height direction, the same direction your printer builds in). A selected shape has a handle, usually a small cone or arrow above it, that raises and lowers it. Grab that and a box can float 5 mm above the workplane. You will use this constantly once we start cutting holes.

So: drag the body of a shape to move it on the ground (X/Y), grab the up-handle to change its height (Z).

The one trick that unlocks everything: holes

This is the most important idea in Tinkercad, and it is the one that makes people go "oh, that is how you do it."

Every shape in Tinkercad can be one of two things: a solid (real plastic) or a hole (empty space). When you select a shape there is a setting that flips it between solid and hole. A hole shape looks see-through, like a ghost, and on its own it does nothing.

The magic happens when you group shapes together. Grouping merges selected shapes into one. And here is the rule: where a hole shape overlaps a solid shape, grouping them carves the hole shape out of the solid. The empty space wins. This operation has a formal name, boolean subtraction, but you can just think of it as "use this ghost shape as a cookie cutter."

This is how you hollow things out, cut slots, drill holes, and carve letters. Let me make it concrete.

Worked example of the hole trick: a simple open box (a tray)

Say you want a little open-topped tray, the kind of thing you toss keys into.

  1. Drag a box onto the workplane. Type its size: 60 mm wide, 60 mm deep, 20 mm tall. This is the solid outer block.
  2. Drag a second box on. Make it smaller: 52 mm wide, 52 mm deep, 20 mm tall. This will become the hollow inside.
  3. Select that second box and flip it to a hole. It turns see-through.
  4. Now position the hole. Center it over the first box (you want even walls all the way around, so 4 mm of solid on each side). Then lift the hole upward in Z by about 4 mm, so its bottom is 4 mm off the ground. That 4 mm becomes the floor of your tray. If you do not lift it, the cut goes straight through and you get a frame with no bottom.
  5. Select both boxes (drag a selection rectangle around them, or shift-click each one) and group them.

The hole box vanishes and takes a box-shaped chunk of the solid with it. You are left with a tray: 4 mm thick walls, a 4 mm floor, open on top. You designed an object that did not exist five minutes ago.

That same move (solid minus hole) is the heart of the lemon squeezer we build later. A squeezer's bowl is nothing more than a big cylinder with a smaller cylinder subtracted out of it, exactly like the tray but round. Keep that in your back pocket.

Combining, aligning, and copying

A few more moves round out your toolkit.

Grouping to combine. Grouping does not only subtract. If you group two solids that touch, they fuse into a single object. That is how you build complex things from simple parts: a handle (a thin box) grouped onto a cup (a cylinder) becomes a mug.

Aligning. Lining shapes up by eye is fiddly. Tinkercad has an align feature: select two or more shapes and it offers to snap them so their centers match, or their edges line up. This is how you get a hole perfectly centered in a block instead of almost centered. Use it whenever "roughly lined up" is not good enough, which is often.

Duplicating and mirroring. You can copy a shape (the usual copy-paste, or a duplicate command) so you do not rebuild identical parts. And you can mirror a shape, flipping it into its reflection, which is handy for anything that has a left and a right side. Design one half, mirror it, done.

Getting the model out: export

When your object looks right from every angle (orbit around and check the bottom and the inside, not just the pretty front), you are ready to leave Tinkercad and head for the slicer.

You do this by exporting the design to a file. The format you want for printing is STL, the most common 3D-print file type. An STL describes the surface of your object as a mesh of triangles. Almost every slicer on earth reads STL, so it is the safe default.

You will also see 3MF offered. It is a newer format that can carry more information (like color or print settings) in one file. If your slicer supports it, 3MF is a fine modern choice. When in doubt, STL works everywhere.

Export, and you now have a file on your computer ready to drop into the slicer.

Start to finish: a name tag

Let us tie every move together into one small, genuinely useful object: a name tag, the kind you could screw or zip-tie to a bag or a shelf.

  1. Base. Drag a box onto the workplane. Type 70 mm wide, 25 mm deep, 3 mm tall. That 3 mm is the plate.
  2. Hang hole. Drag a cylinder on, make it small (say 5 mm across, and a bit taller than 3 mm so it pokes through both faces), flip it to a hole, and move it near one end of the plate. This will be the hole you thread a tie through. Group it with the base to punch the hole.
  3. The text. Tinkercad includes a text shape: drag it on and type your name or initial. Size it to fit, around 12 mm tall, and set its height (Z) to about 1.5 mm so the letters will stand proud of the plate.
  4. Place and fuse. Center the text on the plate using align, and make sure it is sitting on the plate (lift it in Z so its bottom meets the top of the base, not floating, not buried). Then group the text with the base so they become one solid piece. Now you have raised letters.
  5. Check. Orbit all the way around. Look at it from the side to confirm the letters actually rise above the surface. Look from underneath to confirm the base is solid and flat.
  6. Export STL, slice, print. Export to STL, open it in your slicer, set your usual settings, and print. In an hour you are holding a name tag you drew yourself.

Notice that this used the entire toolkit: dropping shapes, typing exact sizes, moving in X/Y, lifting in Z, the hole trick for the hang hole, raised text grouped as a solid, aligning, and exporting. Nothing here was advanced, and yet you produced a finished, useful part.

And that is the whole point. When we get to Chapter 13 and actually design the lemon squeezer, we will not learn any new superpower. A bowl is a big cylinder with a smaller cylinder subtracted (the tray trick, made round). The juicing cone in the middle is, well, a cone shape. The drainage slots are thin hole-boxes grouped away. Every piece of that squeezer is built from the exact moves you just practiced on a name tag.

Takeaways

  • CAD means making the 3D model yourself, the step that turns you from someone who prints downloads into someone who makes originals.
  • The model you build in CAD is what you then feed to the slicer. CAD describes the shape; the slicer makes the printer's instructions. They are separate steps.
  • Tinkercad is free, browser-based, and beginner-friendly: you build by dragging and combining simple blocks.
  • Type exact dimensions in millimeters instead of eyeballing handles, because parts have to physically fit.
  • Learn the camera: orbit, pan, zoom, and always check your object from underneath and inside.
  • The hole trick (flip a shape to a hole, overlap it with a solid, group them) cuts that shape out. This single operation hollows bowls, drills holes, and carves slots.
  • Grouping also fuses solids together; align, duplicate, and mirror save you from rebuilding parts.
  • Export to STL (or 3MF) when you are done, and the file is ready for the slicer.
  • Other tools (FreeCAD, Autodesk Fusion, Onshape, and the code-based OpenSCAD) wait for when you outgrow Tinkercad.

👉 You can draw shapes now, but a model that looks good on screen can still fail on the printer. Next we cover the rules that keep your designs printable: overhangs, wall thickness, flat first layers, and more, in Designing for a 3D printer.