How to Build a Desktop Catapult

Step-by-Step Guide

1. 1

   Step 1: Buy the materials needed for the project.

   See the complete list under Things You'll Need, later in the article.
   
   All the components for this project cost less than $15 (US), and there was no problem finding them.
2. 2

   Step 2: Assemble your tools on a convenient workbench or other suitable location.

   The following were used in this assembly:
   Circular saw Battery and electric drills with bits Sander Hot glue gun Measuring tape Hammer Utility knife , You will need: 1 piece 3/4 plywood, 9X16 inches 2- 1/2 inch diameter dowels, 12 inches (30.5 cm) long 2- 1/2 inch diameter dowels, 18 inches (45.7 cm) long 4- 1/4 inch diameter dowels, 18 inches (45.7 cm) long 2- 1/4 inch diameter dowels, 16 inches (40.6 cm) long 2- 3/8 inch diameter dowels, 7 inches (17.8 cm) long 3- 3/8 inch diameter dowels, 18 inches (45.7 cm) long various spacer blocks cut from the dowels listed above various lengths of twine to lash dowels together while assembling.
   
   These lashings give the catapult its structural soundness. , Mark the board lengthwise at 1 inch (2.5 cm) and 9 inches (22.9 cm) with a framing square or rule, then mark the center line, from which you measure out 3 inches (7.6 cm) either way for the holes. , These holes are drilled perpendicular to the board. ,, These are the holes for the cross beams to fit into. , Drive the 12 inch (30.5 cm) by 1⁄2 inch (1.3 cm) dowels into the holes at the one inch marks, they should intersect the vertical dowels at their tops.
   
   Some carpenter's wood glue applied to the ends of these dowels will help hold them securely in place. , Hot melt wood glue will save a lot of time on this step, and a dab of glue will help secure the lashing twine when it is knotted. , If these are not snug enough, glue them in place. ,, The spaces should be located so that the pivot point is an open space about 1⁄2 inch (1.3 cm) wide, which will be the location for it to be placed on the pivot beam.
   
   Leave another space about 1 1⁄2 inches (3.8 cm) long at the top end of this assembly (the launch arm).
   
   This is where the cup, or projectile holder will fit. ,, This can be carved by hand if you prefer, since it will be a fairly small piece of wood to hold securely while using your power tools for carving. , You will want to be certain to lash this tightly and glue the lashings in place to avoid accidentally launching the complete cup when you fire the catapult. , These will keep the launch arm assembly in line while it swings during launch.
   
   If the arm and pivot bar are tight enough to keep the assembly in alignment, these pieces can be left off. , Adjust the tension so that the launch arm can be drawn back to a horizontal position for loading and firing.
   
   Using a stronger spring will make your catapult more powerful, but this is not always desirable, since it causes a lot of stress on the moving components.
   
   Most hardware stores have an assortment of various springs, so you may need to experiment a bit here to find one that works for you. , Pull back the launch arm and release it from various draws to determine the range and power you are looking for.
   
   If none of the parts become loose or lose tension, you can launch similar size and weight projectiles with remarkable consistency using this device. ,
3. 3

   Step 3: Cut out the following required pieces.

4. 4

   Step 4: Lay out plywood for holes required for the frame

5. 5

   Step 5: as shown in photo.

6. 6

   Step 6: Drill holes with a 15⁄32 inch (1.2 cm) bit to install uprights at the 9 inch (22.9 cm) mark.

7. 7

   Step 7: Drill holes with the 15⁄32 inch (1.2 cm) bit at the one inch marks at a 50 degree angle to the board.

8. 8

   Step 8: Drill one hole with a 5⁄16 inch (0.8 cm) bit in each 18 inch (45.7 cm) by 1⁄2 inch (1.3 cm) dowel at 6 inches (15.2 cm) and 1 inch (2.5 cm) from one end.

9. 9

   Step 9: Drive the 18 inch (45.7 cm) by 1⁄2 inch (1.3 cm) dowels into the holes on the 9 inch (22.9 cm) marks.

10. 10

    Step 10: Glue the dowels together where they meet at the top

11. 11

    Step 11: then lash them with twine for support.

12. 12

    Step 12: 'Taper the ends of the 3⁄8 inch (1.0 cm) by 7 inch (17.8 cm) dowels with sandpaper so they fit snugly into the two holes at the top of the upright 1⁄2 inch (1.3 cm) dowels

13. 13

    Step 13: then spread the uprights to fit them in.

14. 14

    Step 14: Lash the 1⁄4 inch (0.6 cm) by 18 inch (45.7 cm) dowels to the upright 1⁄2 inch (1.3 cm) dowels with twine

15. 15

    Step 15: then hot glue the twine to prevent it from slipping.

16. 16

    Step 16: Assemble the two 3⁄8 inch (1.0 cm) by 18 inch (45.7 cm) dowels together

17. 17

    Step 17: parallel

18. 18

    Step 18: with space blocks between them cut from the same material.

19. 19

    Step 19: Spread the uprights sufficiently to install the launch arm

20. 20

    Step 20: then replace the cross arms

21. 21

    Step 21: gluing them into position.

22. 22

    Step 22: Carve a suitable "cup"

23. 23

    Step 23: or projectile holder from your scrap of 2X4 lumber

24. 24

    Step 24: rough shaping it with a circular saw

25. 25

    Step 25: then rotary rasps

26. 26

    Step 26: and finally a sanding disk or sandpaper.

27. 27

    Step 27: Lash the projectile cup into the notch at the end of the launch arms using the twine.

28. 28

    Step 28: Glue or lash guide pieces for the travel of the launch arm between the two cross beams

29. 29

    Step 29: and from the base diagonally up the path of travel of your arm.

30. 30

    Step 30: Fasten a spring at the bottom of the launch arm to a point on the opposite side of the base

31. 31

    Step 31: using twine.

32. 32

    Step 32: Trim any loose strings

33. 33

    Step 33: check all glue joints

34. 34

    Step 34: and you should be ready to fire.

35. 35

    Step 35: Finished.

Detailed Guide

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