Monday, September 8, 2014
TR-1 Motor Update
This past weekend I finished a few more tasks, although it's starting to look like I may not be quite ready to test fire the motor by the 20th of this month like I was hoping to do. I was hoping to get o-rings by Saturday so I could do a final test fit of the nozzle and bulkhead but I didn't get them on Saturday like I had hoped, but I can do that this week as it shouldn't take long. I did some minor machining on the nozzle to get the two pieces to mate together perfectly. I also took the time to go back and adjust the inlet a bit by machining the inlet at decreasing inlet angles (30, 15, and 7.5 degrees) and then grinding and polishing smooth so the inlet is MUCH smoother and gradual transition to the throat. No change to the throat diameter was made.
I also made two casting bases out of scrap redwood that I had lying around. The casting tubes are held in place securely with a friction fit. In the past I have only used a 1/4" recess but these are a full 1/2" deep so the tubes seem pretty snug. The surfaces of the wood that comes into contact with the tubes/propellant were coated with epoxy. Once cured, they were machined to the final dimensions. This seals the surface from the grease used as a release agent and helps maintain dimensional stability.