How to Build a Catapult

You may need to construct a reasonably sized catapult structure for a school project or for your own personal gratification. The steps to building a catapult are relatively straight forward. Attempt this project with assistance.


  • 9-8’ 2×4
  • 1-12’ 4×4
  • 3-8’ 4×4
  • 50’ of surgical tubing
  • Fibreglass windsurfing pole or a large section of steel pipe
  • 20’ thick nylon rope
  • 1-4’ section of 4” diameter ABS pipe
  • 1-4’ section of 2.5” diameter ABS pipe
  • 2-4” 2.5” step down ABS adapter
  • T-adapter for ABS pipe
  • ABS cement
  • 2”x4” aluminium pipe
  • S hook
  • U bolts and nuts
  • Large eye bolts
  • 12-6” lag bolts
  • 3-5” carriage bolts, buts and washers
  • Assorted deck screws


  • Chop saw
  • Reciprocating saw
  • Drill press
  • Assorted drill bits
  • Drill
  • Wrenches
  • Welder


  1. Create the base of the frame at 3’x8’ cutting the pieces out of the 2×4’ boards. Shape the frame like an off-balance ‘A’ and ensure it is 6’ tall.
  2. The frame should be constructed first, using screws to fit the pieces together at each joint. Connect the 4×4’ to the base frame with lag bolts, ensuring to pre drill them. Use two bolts per post–one through the side of the base frame and the other through the indented 2×4.
  3. Create the back braces with four 8×8” pieces of 2×4. Miter them by 60º on one ends and once they’re cut, screw a pair of them together. Affix them to the frame. Cut 1’ pieces of 2×4 for corner braces and miter them by 45º on both ends. Screw them into the frame corners.
  4. To forego complications, it is highly advised that a cross brace is omitted. Instead bolt two more u-bolts to the top of the posts, facing each other.
  5. Drill the posts (wear protective gear). Do this with extreme precision; if you’re a little off with the hole, you will need to open it up even more, and thus weaken the posts. Slide the aluminium stock into place.
  6. To construct the rotating arm bolder, gather the ABS adapter, 2 sections of ABS pipe and ABS cement. Spread the cement on the inside of the T adapter and on the outside of whatever will fit inside it. Ensure an even coat on both members; do not apply too much.
  7. Compare it to the catapult’s width, centre it, mark the edges and cut off the excess ABS. Drill two holes, perpendicular to each other. Ensure the holes are a bit bigger than your carriage bolts and will be used to hold the arm in place.
  8. Slide the aluminium pipe in and out so the rotating arm holder is able to rotate about it.
  9. Make the winding spool, rope and firing pin a few feet in from the back of the catapults on the upward sloping braces.
  10. Use a sturdy hinge, steel pipe and any carriage bolt or smooth piece of metal to make the firing pin.
  11. Prepare the arm by drilling a few holes in it, and then attach it to the catapult. Drill the holes considering the material that was used to construct it. Slide the arm into the rotating arm holder and put the carriage bolts through the holes drilled.
  12. To finish up, make the catapult mobile by adding wheels, and tie up the structure with surgical tubing.
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