Water Bottle Bazooka

Step 4 Cut the Reduction Coupler

The reduction coupler will eventually go on the back end of the pipe, providing a place to mount a firing mechanism. All we need to do is cut a slot for the modified washer to slip into.

Wrap a piece of masking tape around the narrow end of the coupler. This will serve as a nice high-contrast surface to mark cut lines. With a marker, draw a line across the masking tape - it doesn't matter where. Then, on the exact opposite side of the coupler mark another line.

When you look inside the coupler from the narrow end, you will see a lip. Normally the smaller pipe will hit this lip, preventing it from going too far in. In this case, the washer will be resting on it. With a ruler, measure how far down this lip is on the coupler. In my case, it was about 1.7 cm. Make a mark on each of the lines that is 1.7 cm from the end of the coupler. The slot has to be the same width as the washer. Place another mark on each side of the coupler that is about equal to the width of the washer. Now, scribe a line between each of the pairs of lines. You may want to use a guide of some sort.

Using a saw, cut out the slot as carefully as you can. The washer should slide in easily, but should not wobble around. When you have completed the cut with a saw, you may need to widen the slot just a bit with a sharp knife. BE CAREFUL when you do this - ABS plastic doesn't really like being cut in this way and your blade may slip. Cut away from yourself, and make sure that either both hands are on the knife or keep one hand away from the work piece.

When you're done, the washer should slide in about halfway into the coupler. Slide in a bottle and make sure that it cannot be pulled out while the washer is in place.