Build a cam or crank machine
Build a simple cam or crank machine from cardboard, dowels, and glue; observe motion changes, test different cam shapes, and learn mechanical motion principles.
Step-by-step guide to build a cam or crank machine
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Step 1
Lay out all materials on a clean table so everything is easy to reach.
Step 2
Cut a rectangle of cardboard about 20 cm by 15 cm to be your machine base.
Step 3
Use the ruler and pencil to mark a center line along the long side and mark two shaft positions about 3 cm from each short end on that line.
Step 4
Cut two small cardboard blocks about 3 cm square and glue each block onto the marks to make the shaft supports.
Step 5
Carefully make a straight slot or hole through each support where the dowel will sit using scissors or a craft knife with an adult helping.
Step 6
Cut a wooden dowel to the length of the base plus about 4 cm and place it into the support slots so it turns like a shaft.
Step 7
Cut three or four cardboard circles about 4 to 6 cm across to use as cam blanks.
Step 8
Draw a different cam profile on each circle such as a centered circle an off-center circle an oval and a lobe shape.
Step 9
Cut out each cam shape carefully along the profile lines.
Step 10
Poke a center hole in each cam and slide them onto the dowel spacing them apart then secure each cam to the dowel with a drop of glue or tape.
Step 11
Make a follower by taping a bottle cap or washer to the top of a short vertical stick or dowel so it can press against the cam surface.
Step 12
Position the follower next to one cam so the cap just touches the cam surface and secure the follower upright on the base with tape.
Step 13
Turn the shaft slowly by hand and watch how the follower moves for this cam then remove and replace cams to test and compare how different shapes change the motion.
Step 14
Share a photo or video of your finished cam and crank machine on DIY.org
Final steps
You're almost there! Complete all the steps, bring your creation to life, post it, and conquer the challenge!
Help!?
What can we use instead of a wooden dowel or craft knife if we can't find them?
If a wooden dowel isn't available, use a straight pencil or a sturdy chopstick cut to the base length plus about 4 cm for the shaft and, if you don't have a craft knife, an adult can carefully enlarge support slots with scissors as described in the step making the shaft supports and slots.
The cams keep slipping on the dowel or the shaft won't turn smoothly—what should we try?
If cams slip or the shaft doesn't turn smoothly, add a small wrap of masking tape or a tiny dab of hot glue inside each cam hole when you slide them onto the dowel (the step that secures each cam) and check the support slots are straight and not too tight so the dowel can rotate freely.
How can we adapt this activity for different ages or skill levels?
For younger kids, have an adult pre-cut the 20×15 cm base, 3 cm blocks, and cam blanks and use tape instead of glue during assembly, while older kids can draw more precise cam profiles, stack multiple cams on the dowel, and measure follower motion to compare outcomes.
How can we extend or personalize our cam and crank machine after it's built?
To extend and personalize the project, decorate the cardboard base and each cam before assembly, attach the follower (bottle cap or washer on a short dowel) to a paper character, and add a second follower on the same shaft to create coordinated movements when you turn the shaft during testing.
Watch videos on how to build a cam or crank machine
Simple Machines:Levers
Facts about simple machines and mechanical motion
🛠️ Cams turn round-and-round motion into up-and-down or back-and-forth motion — that's how many pop-up toys and music boxes work.
🔩 Cranks have been used for centuries to lift heavy loads by hand and were a key tool in early mills and water-raising devices.
📦 Corrugated fiberboard (cardboard) is light but very strong when folded or layered — that’s why it's great for building sturdy DIY models.
🎶 Car engines use camshafts with multiple cams to open and close valves at just the right moments so the engine runs smoothly.
🔁 Swap a circular cam for a heart-shaped or snail cam and you'll see very different follower motions — cam shape controls the timing and movement style.
