Build a Mechanical LEGO Valentine Box

Is your child tossing around Valentine box ideas, trying to decide how to decorate their box? Well, how about just building a Valentine box out of LEGO bricks? SO FUN!

In fact, this is a mechanical LEGO Valentines Box, which means that it has moving parts. Turn a gear on the side of the box, and the envelope slot opens. How cool is that?! The mechanism is very fun, and easy to make. However, kids can easily build this box without the mechanism and just leave a slot open on the top.

Here’s how the LEGO Valentine Box works:

The top of the box has a slot. Underneath the slot, there is a gray panel that slides back and forth to open the slot. There are two gear racks on the panel that make it move. I’ll show you more photos (and a video) in a minute!

As you turn the gear on the side of the box, the panel slides…

And then you can drop in a Valentine card!

Want to see a video demonstration? Click the play button and watch how our LEGO Valentine Box works.

Can’t see the play button? It’s probably because of ad blockers. Ads on the videos allow me to keep this website free, rather than charging a membership fee.

Ready to build your own LEGO Valentine Box?

Kids can use whatever color bricks they want for this project. My boys have never been into hearts and mushy stuff… while Janie loves red, pink, and hearts. It will be fine to make it red with hearts, or make it a combination of colors! One alternative to hearts would be to build a yellow emoji face into the design.

Start with a 32 x 32 baseplate. Our box is 24 x 24 studs. Kids can adjust the size however they like.

There are two white plates that I built into the sides of the box to serve as “bumpers” for the sliding panel. You’ll see why in a minute when I explain more.

I made the front of the box solid red, and the sides red and white stripes. The back is light gray simply to cut down on how many red and white bricks I needed! No one looks at the back, haha.

We had some cute heart plates from the LEGO store, so I attached those to the box with 1 x 1 bricks that have a stud on the side.

I also put two 1 x 8 Technic bricks on the side of the box so that I would have a hole to run an axle through.

The sliding panel needs a track to slide on. I made two “towers” out of bricks. There are tiles on top of each one, and a bracket on one end. The bracket keeps the panel from sliding too far and falling off.

Place one brick tower on each side of the box. Mine are three studs from the back.

I built the panel by connecting a 4 x 8 plate and an 8 x 16 plate. There is a plate underneath that connects them. Then I added two 1 x 4 gear racks.

Place the panel on top of the brick towers. Make sure that it can slide back and forth freely.

Grab an axle (5 studs long), a 12-tooth bevel gear, a red Technic bush, and a 40-tooth gear.

Note: You can substitute something else for the 40-tooth gear if needed. Kids will notice that turning just the bare axle will be challenging. You need to create some mechanical advantage by placing a larger circle on the axle. Then it will be much easier to turn!

Slide the axle through the Technic bricks on the side of the Valentine box. Then slide on the bevel gear so that the teeth mesh with the gear rack as shown. Finally, add the 40-tooth gear.

This is the full mechanism. When you turn the 40-tooth gear, the panel will slide back and forth between the light gray brackets and the white plates.

Add a layer of plates all the way around the top of the box. This will allow you to add a lid without it touching the black gear.

Then build a lid for your Valentine Box! I connected several white plates together. If you don’t have enough white, gray will work well, or you can choose a combination of colors.

And then you’re all set for your class party!