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Build a soap box car

Build a soap box car
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Build a small soap box car from wood or cardboard, attach wheels and axles, learn basic tools and test rolling performance with adult supervision.

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Step-by-step guide to build a soap box car

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DIY Soapbox Car

What you need
2 short pieces of straw or 2 small wooden blocks for axle holders, 2 wooden dowels or skewers for axles, 4 bottle caps or 4 small toy wheels, adult supervision required, colouring materials, craft knife or small handsaw, pencil, ruler, safety goggles, sandpaper, small piece of lightweight wood or sturdy cardboard, strong glue or hot glue gun

Step 1

Put on your safety goggles

Step 2

Choose whether to build your soap box car from wood or from cardboard

Step 3

Measure and mark a rectangle about 20 cm long and 10 cm wide on your chosen material using the ruler and pencil

Step 4

Cut out the rectangle along your marks using a handsaw for wood or a craft knife for cardboard with adult help

Step 5

Sand the edges and corners of the chassis until they are smooth

Step 6

Measure and mark the centerline and place two marks about 3 cm from each short end where the axles will go

Step 7

Make axle holes at the marks by drilling small holes for wood or carefully poking holes for cardboard with a craft knife or awl with adult help

Step 8

Cut two wooden dowels or skewers to be slightly wider than the chassis and sand the ends

Step 9

Make holes in the bottle caps or wheels and push the dowels through each pair of wheels and secure them with a small dab of glue so the wheels stay on but can turn

Step 10

Slide each axle with its wheels through the chassis holes so the wheels sit under the car and can spin freely

Step 11

If the wheels rub or wobble adjust the axle position or add short straw bushings under the chassis until the wheels roll straight

Step 12

Decorate your car with paint or colouring materials and let it dry completely

Step 13

Test your soap box car by rolling it down a gentle ramp or smooth floor and watch how fast and straight it goes

Step 14

Make one small improvement like tightening a wheel or shifting an axle and test again

Step 15

Share your finished soap box car on DIY.org

Final steps

You're almost there! Complete all the steps, bring your creation to life, post it, and conquer the challenge!

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Help!?

What can we use if we can't find wooden dowels, bottle caps, or a handsaw?

If you can't find wooden dowels use bamboo skewers, chopsticks, or straight pencils as axles, replace bottle-cap wheels with jar lids or old toy car wheels, and swap a handsaw by buying pre-cut wood or building the chassis from cardboard cut with a craft knife by an adult.

What should we do if the wheels rub or wobble or don't spin freely?

If wheels rub or wobble, adjust the axle position as the instructions suggest, sand the dowel ends and wheel holes, ensure the axle holes are straight when drilling or poking, and add short straw bushings under the chassis so the wheels roll straight.

How can we adapt this project for younger or older children?

For younger children use a pre-cut cardboard chassis, tape or school glue instead of strong adhesives, and adult help for cutting and making holes, while older kids can cut and sand a wooden chassis, drill precise axle holes, and fine-tune axle alignment and wheel sanding themselves.

How can we enhance or personalize the soap box car beyond the basic build?

Enhance your car by decorating with paint and stickers as instructed, smoothing aerodynamic edges, trying larger or lighter wheels, adding a removable weight to test speed, or building a simple steering or brake using extra skewers and straws.

Watch videos on how to build a soap box car

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Soapbox Derby Race Car Building Tips

4 Videos

Facts about woodworking and basic mechanics for kids

⚙️ The wheel-and-axle is one of six classic simple machines and helps tiny cars roll much more easily.

⛰️ Soap box cars race without engines: gravity turns height (potential energy) into speed (kinetic energy) as they go downhill.

🧴 Dry graphite or small bearings are common lubricants in youth races because they can cut axle friction and speed up a run.

🚗 The first Soap Box Derby kicked off in Dayton, Ohio in 1934 and made kids' gravity racing famous across the U.S.

🪵 The Pinewood Derby — a pint-sized wooden-car race — was invented by Cub Scout leader Don Murphy in 1953.

How do you build a soap box car?

Start by sketching a simple car shape and measuring the wheelbase. Cut the body from plywood or thick cardboard, and sand edges smooth. Mount two axles (metal rods or wooden dowels) straight across the chassis, secure with blocks or brackets, then attach wheels so they spin freely. Add a lightweight seat and steering (rope or simple pivot). Test and adjust alignment on a short flat run, always with adult supervision when using tools.

What materials do I need to build a soap box car?

Gather materials: a sheet of plywood (1/4–1/2") or sturdy cardboard, four wheels (toy or purchased), two axles (metal rods or wooden dowels), screws/bolts, wood glue or strong adhesive, small blocks for axle mounts, sandpaper, paint and brushes. Tools: measuring tape, pencil, saw or utility knife, drill, screwdriver, clamps. Safety gear: adult supervision, work gloves, eye protection. Substitute lightweight items for easier builds.

What ages is a soap box car project suitable for?

This activity suits children about 6 and up with heavy adult supervision. Ages 6–8 can help design, paint, and assemble simple parts while adults handle cutting, drilling, and fastening. Ages 9–12 often manage more tool use with guidance and learn measuring and problem-solving. Younger children can participate in safe tasks like decorating and testing. Always match tasks to the child's motor skills and comfort with tools.

What safety tips and fun variations are there for a soap box car build?

Safety first: always supervise tool use, wear gloves and eye protection, clamp pieces before cutting, and test on flat, obstacle-free areas. Check wheel tightness and rounded edges to avoid splinters. Variations: build with cardboard instead of wood, add a pull-rope steering, create a gravity racer for slopes, or host a timed obstacle course. For younger kids, pre-cut parts so they can assemble and decorate safely.
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Build a soap box car. Activities for Kids.