A storage box

You will make an 80 × 60 × 40 mm storage box with 3 mm walls and a 4 mm floor, then change its numbers so it follows. It builds on Your first part, so sketch a plate first if you have not. It takes about 20 minutes.

This one shows the other half of Extrudo's idea. You sketch once on the floor, give the sketch height, and then sketch on the top of the solid to hollow it out. The walls are a parameter, so making the box wider moves the walls with it.

Open the app at https://app.extrudo.org.

1. Start a design and add your numbers

On the home screen press New design. Press the name at the top, type Storage box and press Enter. Open the Home tab and press Parameters.

Add these five, the same way as before (a name, the unit on Length, an expression, Add):

Press Esc to close the dialog.

2. Start a sketch on the floor

Open the Solid tab, press Create Sketch and choose the XY plane, the floor of the model. The view turns to look straight down on it.

Scroll to zoom out a little so the whole box will fit, and drag with the right mouse button to move it to the middle, clear of the palette. In the Sketch palette on the right, switch Show constraints off: the little symbols would crowd this tutorial.

3. Draw the base

Press Rectangle (or R). Click the origin, where the green and red lines cross, then click the opposite corner at 80 mm across and 60 mm up. Press Esc to finish the rectangle.

The corner you started on is pinned to the origin, and the grid snaps your clicks to 10 mm steps.

4. Size the base with your parameters

Press Dimension (or D). Click the bottom edge, click below it to place the label, type width and press Enter. Then click the left edge, click to its left, type depth and press Enter. Press Esc to leave the tool.

The palette reads Fully constrained ✓: the two dimensions pin the whole rectangle, so the box will follow width and depth when you change them.

5. Give the base its height

Press Finish Sketch. Click the plate's inside to select its shape and press E (Extrude). Press Shift+1 to look at it from the corner, then type height in Distance. The preview shows a solid 80 × 60 × 40 mm block; the default Operation is New body, which is what you want.

6. Press OK

Press OK. You now have a solid, Body1, and Extrude1 joins the timeline. It is 80 × 60 × 40 mm with 6 faces: top, bottom and four sides.

7. Start a sketch on the top face

Now the interesting part: drawing on the solid itself. Press Create Sketch again, and this time click the top face of the block instead of a plane. The view turns to look straight down on the face, and Sketch2 appears in the timeline. The face fills the view: scroll out a little and drag with the right mouse button until it sits in the middle with room around it.

8. Project the face's outline

Press Project (or P), then click the top face. Extrudo copies the face's outline into the sketch as its own four lines, in the construct colour. They are tied to the face, so they move when the box does. Press Esc to leave the tool.

9. Offset the outline to make the walls

Press Offset (or O). Click the projected outline, then move the pointer to the inside and type 3, the wall thickness. Press Enter: a second, smaller rectangle appears 3 mm inside the first, and the palette now shows 2 profiles.

Double-click the dimension under the inner rectangle and type wall instead of 3. All four dimensions follow it, so every wall will be one parameter.

10. Cut the cavity

Press Finish Sketch. Click between the two rectangles to select the inner profile, and press E (Extrude). Set Operation to Cut, type -(height - bottom) in Distance and press OK. The extrude cuts the cavity down to the 4 mm floor. Press Shift+1 to look at the box from the corner. Body1 now has 11 faces: the six outside, four inner walls and the floor.

11. Change a number and watch the walls follow

Open the Home tab, press Parameters and change width to 100 mm, depth to 70 mm and wall to 4 mm. Press Esc, then Shift+1 to bring the bigger box back into view.

The box is wider and deeper, and the walls are thicker, because the offset sketch follows wall. The floor stays 4 mm. Ctrl+Z undoes the change if you prefer the old size.

12. Export for printing

Open the 3D Print tab and press Export. Choose STL. The summary says the model is watertight, which means a slicer can read it without repair. Press Export STL and the file downloads.

What you learned

• A sketch can sit on the top face of a solid, not only on the origin planes.
• Project copies a face's outline into a sketch, tied to the model.
• Offset grows or shrinks an outline in one step, and its dimension can follow a named parameter.
• An Extrude can Cut a cavity into a body instead of adding material.
• The timeline keeps every step, so changing a parameter recomputes the whole box from the start.

Related tools: Parameters, Create Sketch, Rectangle, Dimension, Extrude, Project, Offset and Export.

The ideas behind this tutorial are in The app in five minutes, Sketching and constraints, Features and the timeline and Parameters and expressions.