The following information is a single lesson in a larger Tinkercad project. Check out this and more projects on Tinkercad.

Project Overview:

This project shows you how to modify an existing design for an Ardunio Uno case and add new features.

Step 1: Find the Right Part to Put Into Tinkercad

Thingiverse.com is a great starting point to find 3D content ready to modify.

Instructions

Navigate to http://www.thingiverse.com/thing:628929 to see the part we will be making changes (or modifications) to.
Save the file(s) as an .stl somewhere on your desktop (or any folder you want to point Tinkercad).
Stuck?

HINT:

When searching for parts, you want to use plain English. To find my part I simply searched for "Arduino Box".

Step 2: Bring the Part Into Tinkercad

Import the .stl file(s) into Tinkercad

Instructions

Expand the "Import" panel found on the right side of the screen.
Click "Import" and browse to the location where you saved the file on your computer. This will import the file into the Tinkercad environment.

Step 3: Place a Temporary Workplane

Place the Workplane on a flat surface you want to modify.

Instructions

From the "Helpers" panel on the right side of the screen, click and drag the blue rectangle Workplane over a flat part (face or plane) of the area you want to modify. In this case, the bottom inside surface of the box. This Workplane is temporary and can be removed by dragging a new workplane to anywhere that is not a face or plane on the Tinkercad shape.
Stuck?

HINT:

When the workplane is placed correctly it will obscure the view of the bottom of the box. This is so you can position shapes on the surface you want.

Step 4: Remove Material With Bevels

In this step, you will use a Roof shape to remove material from the inside of the existing box.

Instructions

Drag over the green Roof shape and position it so just clips the edges of the inside of the box. The holes should slightly covered as well.
Stuck?

HINT:

This is where you can save a lot of time. You don't need to worry how high a part is when it is going to become a hole because the part of the hole not intersecting the shape does not affect the modification.

Step 5: Hollow Out Walls With Box Shapes

Making rectangle shaped holes in the walls of the box.

Instructions

Drag a Box shape onto the work plane and shape it so the width and length define the hole you want to make. In order to do this you will need to rotate the Box shape so one of the two triangle sides is facing down and touching the Workplane.
Stuck?

HINT:

Remember: 1) It is easier to keep a future hole as a solid while you drag it around 2) You don't need to worry about an exact height for holes as long as they are taller than the surface you are trying to modify.

Step 6: Putting Holes in the Pillars

Removing extra material inside of the mounting pillars.

Instructions

Drag a Cylinder shape onto the work plane.
Adjust this so it is 1mm in diameter. You will need four of them. Again, do not worry about the height of the cylinders as long as they are tall enough to cut through the tops of the pillars when they are converted to holes.

Step 7: Zoom Out, Tilt and Pan to Check Modifications

The last step before export is to "walk around" your part to make sure that the modifications look right from all angles.

Instructions

Use the Shift+Right Click or Click+Drag the middle mouse button to pan (move side to side). Right Click + Drag to rotate and the Scroll Wheel to zoom in and out.
Navigate around the part to confirm everything looks correct.