Making Nozzles in PVC Pipe fittings from Durhams Rock Hard Water Putty and Graphite plate

A single use rocket nozzle can be made using Water Putty and a graphite plate in a 2" PVC Pipe fitting.  Durhams water putty is a gypsum based putty that exhibits very little shrinkage while drying and is effective as a single use nozzle for motors up to 4" in diameter. 

Supplies:

• 2" PVC Coupling
• 2" PVC to 3/4" threaded female reducer
• Water putty
• 1/4" thick graphite plate ~1"x 1" ( 3/8" ID fender washer can be substituted, but it adds additional complexity)
• Screwdriver or chopstick for mixing
• 2 spoons
• duct tape
• mixing cup
• Safety glasses
• nitrile gloves or equivalent
  

1. Wear safety glasses and nitrile gloves
   
2.  Use PVC primer to coat the surface of the reducer and the PVC coupling up to the ridge joint.
3. Use PVC glue to coat the surfaces and then press the PVC reducer into the coupling.  Hold for at least 20 seconds so that the reducer doesn't float out of the coupling.
   
4.  Cover the small hole in the bottom with duct tape to retain the putty, it is recommended to use at least two layers of tape. 
5. Place the coupling with the duct taper covered hole on the table in front of you.
   
6. Pour about 3/4 cup of Water putty into a mixing cup.
7. Add about 1.5 oz of water
8. Mix completely until it is about the consistency of peanut butter.(~100,000 cps)  If necessary add small amounts of water using a teaspoon.   
   
9.  Use the teaspoon to throw a heaping spoon of putty into the bottom of the threads.  Use the chopstick or screwdriver to work the putty into the threads to get good retention.  Tap the fitting against the table a few times to help settle any air bubbles.
10. Working quickly add additional spoons of putty and tap the fitting vigorously on the table to allow air bubbles to reach the surface. Continue adding putty until it is at the level of the ridge joint in the coupling.                                   
    
11. Place the graphite plate in the middle of the putty and press it flush with the surface.  If the fender washer is to be used, it must be centered exactly in the putty. 
12. Use the clean spoon wetted with a bit of water to work the putty over most of the surface of the graphite. 
13. Clean any putty from the sides of the fitting.
14. Set the finished nozzle aside for at least 24 hours to dry.  

The next day you will drill a 3/8" hole through the center of the now hard putty and graphite.  This nozzle will have a 90o converging angle and a 0o diverging angle, however, on firing, the propellant will quickly erode the diverging segment of the nozzle to create a reasonable parabolic diverging element.