AMP-1 Rocket Engine

Over a couple of swift workdays, the fuel tank was completely welded and the subsequently hydro-statically tested. The welding was a relatively quick process but hydro testing was not. A few small pinhole leaks were found along the weld seam that weren't concerning to the structural safety of the tank but more of the fact that kerosene would be dripping out over time. After a couple of unfruitful re-welding attempts, finally the leaks were sealed and the tank passed its hydro at 1.5x the working pressure. So at 450 PSI everything is good which means the tank is safe to operate at 300 PSI during the engine firing.

Some work was in order to begin testing the servo motor ball valves properly with a specifically machined coupling to interface the the servo shaft to the ball valve stem. A .3125" hole was drilled in the center of one side for the servo shaft to a depth of roughly .600". On the opposite face, a .305" slot was milled roughly .400" deep to accept the square end of the valve stem. A 1/4-20 tapped hole for a set screw was threaded in the servo shaft hole. This will probably be changed to a larger 3/8-24 set screw so there is limited play in the coupling and it will also eliminate the small key that was designed to fit in there. 

It seems that crunch time has been reached in regards to getting this project done on time. The next few days is going to be evaluating what still needs to be purchased to completely test the engine and purchasing necessary items. To move along the test stand, the fuel tank is going to be welded and the subsequently hydrostatically tested so the feed lines can be run and tested at pressure. The propellant control valves needs to be finished up and tested as well. A big couple of weeks are coming up here.

The new boring bar nearly fits inside the throat of the engine but is small enough to cut the entirety of the convergent nozzle geometry. The only downside to this new boring bar is it is small; at only .25" in diameter and cantilevered out approximately 3.5", it is vulnerable to flexing under cutting loads. This could damage the tool and/or the part. To mitigate the problem, shallower cuts were taken. In all, the machining process took more time but it was done without a major issue. The only problem that was seen was there seemed to be a resonance frequency reached in the part that machining a pattern into the combustion chamber wall in one section. For future reference, the speeds, feeds and rpm's can probably be changed to resolve this. 

The machining process for the combustion chamber was broken down into two parts as there were some issues discovered while machining that caused the piece to be uncompleted for the time being. Some new tooling was purchased to solve the problem. Anyway, the combustion chamber round stock was set up in the chuck to face the part. This allowed a reference surface to be determined when the stock was re-chucked with the faced side pressed against the chuck jaws. The opposing surface was then faced and the length of the stock was turned down to the near final length. A center hole was drilled out undersized from the throat diameter to a depth of roughly 2-1/2". With the top slide set to 12 degrees, the divergent cone was cut to open up to a diameter of roughly .95" at the base of the cone. The throat was then roughed out to around .020" undersized from the final dimension with the boring bar.

Before machining started, a redesign was in order to make it easier to machine the small injection orifices for the impinging streams. The problem was that three .028" holes needed to be drilled at a 30 degree angle. This is already a difficult task but the equipment I have to my disposal wasn't going to cut it because I had no accurate way to hold a drill bit that small. So, the three orifice design was scrapped and replaced with a single central orifice that is .047" in diameter. This orifice is perpendicular to the injector face and is impinged by the same three oxidizer orifices. After the redesign, it was time to start working on machining the different geometries that make up the injector. The first thing to be accomplished was to face off both ends and machine the disk to the proper width. After that was complete, the center boss for the o-ring was roughed out and the recess was cut. The whole recess was not machined to the drawing specifications because it w...