## Saturday, May 23, 2009

### Water Rocket Launcher Construction Tutorial: Part 9

Hello again, and welcome to the 9th part in our Water Rocket Launcher Build. This week we are going to star assembly of the PVC plumbing section of our water rocket launcher with the wood base. If you are just joining us, you should go back to part 1 of this tutorial and get caught up on the previous steps.

The first thing we need to do for this part of our project is to find the center line of the main body board of the base. The easiest way to do that is to measure the width of the board and divide by two and then mark this width near each end of the board and use a ruler or some other straight edge to draw a line the length of the board making the center line. This mark will insure that the launcher turns out perfectly symmetrical when finished. If you have a calibrated eyeball you can visually locate the center line of the board.
We will next need to find the center point of our main launcher body board, using the same method. We will measure the length of this board and then put a mark on the center line we just made at the point 1/2 of the length. This will give the exact center of the board and will insure the plumbing is mounted in a nice symmetric way.
We are now going to locate the U-Bolts which will hold the plumbing down onto the main body board. The location of these bolts is trivial math, because we too care in the earlier steps. Remember the length of the main PVC pipe at the bottom of the launcher? Well, we will be using that length now to precisely locate our U-Bolt holes.

Starting at the center point we marked on the base board, we will measure along the center line to locate the U-Bolt locations. The locations we want are exactly half the length of the PVC pipe which we recorded earlier. In our case we had an 8 inch long pipe, so we mark the board 4 inches from the center point on moth ends. We use our carpenter's square to make a line where each U-bolt will go. This line will be the center of the drilled holes for each U-Bolt, so we want to make the line as straight as possible and at a right angle to the board.
When finished making both locations for the U-Bolts, you can check your work by measuring the distance of each U-bolt from the end of the board closest to the spot. The two measurements should be equal. In out case our U-Bolts are each 3 inches from either end. If we were to place the 1/2"x3"x4' plank we want to use for the legs on either end of the board we can also test that the holes are not going to interfere with the mounting of the legs.
To locate the holes for the U-Bolts on the lines we just drew, we will simply measure the width of the U-Bolts and divide by 2. This will result in the distance from the Main body board center line we must mark out on each of the drill lines we just made.
We now can measure the distance for each side of the U-Bolt along the drill lines and mark the positions. These locations are the places where we will be drilling holes for our U-Bolts. Carefully mark each hole location on the drill line for each end of the board. This will produce the hole locations we need for the two U-Bolts.
Check your work by laying a U-Bolt on the board next to the drill marks we just made and verify that the drill marks really do line up with the tips of the threaded parts of the U-Bolt.
Now you are ready to drill out the holes for the U-bolts. Our U-Bolts have take 1/4" nuts, so we want to make sure we drill the holes that are large enough to accept the U-Bolts. We picked a 5/16" drill bit so that our holes will have 1/16" tolerance. If you think you will not be able to drill your holes with that much accuracy, you can pick a larger drill bit which will give you some additional tolerance.
Loosely install the U-Bolts in the holes, and make sure everything fits properly. It's a good idea to put everything together in this way to look for possible problems with clearance or alignment issues. If necessary, you can drill out the holes you just made a bit larger with the next larger size drill bit if you have overestimated the accuracy of your drilling skills.
That's all for this week! We're doing some test flights this weekend, so we have a lot of work to do preparing for the launches and analyzing the test data. We will be posting some launch results as well as a new build we have invented using an incredible new adhesive we discovered. We will also be finishing up the assembly of this launcher tutorial and showing how the design can be personalized. We have a lot of great things in store!

See you next week!