Core A Assembly

These are archived instructions are for the high-performance Type A Core, originally released in 2021. Core A is no longer recommended for new builds, as Core C has identical performance characteristics with a simpler build process and universal bottle compatibility without Clamp changes.

Step 1: Prepare PVC pipe

Left to right: Scissors-type PVC pipe cutter; ruler; 120-grit sandpaper; marking pen; upper and lower sections of 1/2″ nominal PVC pipe (size pictured does not match current design).

1a. Mark a 7.0cm length of pipe (lower tube) and a 15-20cm length (upper tube) of pipe

1b. Cut the pipes squarely. I have had the best success with the above scissors-type PVC pipe cutters. Squeeze lightly and rotate the pipe to score it before cutting through. Alternately, you can use a spinny cutter made for copper pipe or a miter box and saw. Ratcheting PVC cutters can be inconsistent with squareness.

1c. Sand outer cut edges of PVC pipe so they are smooth and not sticking out.

Note: 7.0cm pipe should be cut within 2mm of specified length for internal components to fit properly. 15-20cm pipe is not sensitive to length as long as it fits in your bottle.

Step 2: Prepare Tube Core

Clockwise from top left: Printed 7/16″ hex wrenches that fit 1/4-20 bolts; Tube Core; 1/4″ stainless steel/nylon locknut; 1/4-20 stainless steel bolt, 2.5″ long.

2a. Insert the bolt as shown below, noting the taper of the center section of the Tube Core. Insert the bolt from the top flat side. The nut goes on the bottom angled side.

Note the taper in the center. Nut goes on the angled side.

2b. Use the printed 7/16″ wrenches to tighten the nut as below. It should be snug, but not so tight you strip the plastic wrenches. The handles are intentionally short.

Step 3: Prepare Valve

3a. Get the TR414 Tire Valve and cut off the “mushroom” stopper end right at its edge. Discard the “mushroom”.

Cut off the bottom stopper from the TR414 Tire Valve. It’s fine if the cut is not perfectly flat. As long as the built-in O-ring is intact, the valve will work. Discard the round portion on the right.

Step 4a: Check tubes and components

Top to bottom, on top of a disposable work surface:

7.0cm and 15-20cm PVC pipe
Assembled Tube Core
Valve Holder, Valve, Valve Backstop (old style)
PVC primer, cement, paper towels
Gloves, cotton swabs (not pictured)

There will be three cementing steps. Option 1: Do them in rapid succession (within a few minutes) and then hold the whole assembly under pressure. Option 2: Do them one at a time and give time for the bond to partially cure (30 minutes) before doing the next bond. Consider this if you are new to PVC pipe work so you don’t feel time pressured.

Before starting, check your materials and workspace. Check that your pipes are squarely cut. Have extra paper towels on hand. Read instructions on the primer and cement bottles. Watch instructional YouTube videos as needed on cementing PVC pipes.

Step 4b: Bond Tube Core to 7.0cm Lower PVC pipe

First picture: Note directionality. 7.0cm pipe is the lower tube and connects to the angled side where the nut is. Follow the primer and cement directions. Really saturate the lower part of the Tube Core with primer, including in the groove below the angled taper in the center. This helps wick the cement into the tiny gaps between the layers of PLA.

Second picture: Apply a generous coat of cement to the Tube Core. Don’t get too much near the end where the air passages are, though even if you block one or two up it won’t matter. Insert the Tube Adapter into the primed 7.0cm pipe. Squeeze them tightly so the PVC pipe slides under the edge of the angled center part. Hold for 30 seconds then wipe off the excess cement. You can move quickly onto the next step or allow 30 minutes to cure.

Step 4c: Bond Tube Core to Upper PVC pipe

Now apply primer generously to the remaining Tube Core, including the center bevel and rings. The primer will pull the cement into the nooks and crannies. This provides the airtightness needed.

Apply cement to the Tube Core, including the center bevel and rings. Again, don’t get too much on the air passages, but don’t worry even if you block up one or two. Insert the Tube Core into the upper PVC pipe. Hold for 30 seconds then wipe off the excess cement. Use an edge of a folded paper towel to clear out the groove. The O-ring will be installed here later. You can proceed to the next step or wait 30 minutes for the bond to cure.

Step 4d: Insert the Valve Backstop

Slide the Valve Backstop into the lower 7.0cm PVC pipe. This prevents the Valve from sliding in too far by accident. It should slide in smoothly. It does not need cement.

Note that an an older version of the backstop is pictured. Updated version has a crenellated shape.

Step 4e: Partially insert the Valve

Insert the Valve halfway (about 1-2cm) up the Valve stem. It will fit snugly and slide with some resistance.

Step 4f: Prime the inside of the 7.0cm pipe with a swab

Dip a cotton swab in the primer and swab the inside of the PVC pipe. This takes some finesse and angling the Valve to the side to make space for the swab. Twist the swab to help it orbit around the Valve.

Step 4g: Bond the Valve Holder to the 7.0cm pipe

Prime the outside of the Valve Holder, then apply cement to it. Slide it over the Valve and keep pressing until it is flush with the end of the PVC pipe. It will likely push in the valve a little more. Make sure there is still some stem of the Valve sticking out through the Valve Holder. The Valve Backstop should take care of this. Hold for 30 seconds. Wipe off excess cement.

Step 4h: Compress the entire assembly together and hold for 1 minute

Press on the Valve Holder, not the Valve. Compress the entire assembly.

Step 4i: Allow assembly to cure for 45 minutes

Read the cement directions and follow those for cure times.

Done! Purple primer gets everywhere, but it doesn’t interfere with function.

Step 5: Install O-ring

Stretch the O-ring over the top (long) end of the Launch Tube and roll it down until it sits neatly in the groove.

Top: Launch Tube with O-ring partially rolled on

Bottom: Launch Tube with O-ring seated in its groove (hard to see – just to the left of the purple smudge)

Done!

You can launch water rockets directly off this tube. Slide a bottle on over the O-ring, hold it onto the tube with your hands, have an assistant pump up the bottle, and launch!

This was the hard part. The rest is easy by comparison.

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