Take your two 24 inch pieces and your two 7 1/2 inch pieces and screw them together as shown in this picture. Make sure that the notches you cut in the wood are on the outside of the assembly, not on the inside. Screw one of your big eye hooks into the end as shown. Make sure it is on the end nearest the slots and hole you cut in the long pieces. You can nail these pieces together but Screws are much better. Drill a pilot hole if you have difficulty getting the screws in. A pilot hole is a very thin hole drilled as a starter. It makes it easier for the screws to go in.

Now screw the two upright pieces into place.

Now screw your 10 1/2 inch piece across the top of the two uprights. Make sure it is on the side shown. It should not be on the side nearest the metal hook.

Now take the final 14 inch piece of wood and custom cut the ends so they are at an angle then screw it directly in place like shown.

This cut can be a little tricky but just carefully measure it by holding it up against the catapult and drawing lines on it. The piece shown here has already been cut at both ends with the right angle and just needs to be screwed in place. This piece is rathe important because it adds a lot of strength to the catapult.

Okay, Lets build the swing arm and install it