The body of the rocket is real easy. The tank and combustion chamber of the majority of the rocket. Both the tank and combustion chamber are made using 4 inch .125 wall 6061-T6 aluminum tube. The CC chamber is about 24 inches long with the boat tail screwed all the way onto the CC chamber. The nice thing is these parts, the boat tail and CC chamber where already made by Jeff. He had one left over from another project so he sent me this one for no charge. The tank just had to have the end squared up. So I just chucked it up in the lathe and cut very little of the ends off. I then faced off the ends and it was ready to be polished.
The tank closures/couplers had to be made. The was a lot of fun (NOT). It took a long time and patients to make the two couplers on the lathe. I am using a modified version of what Jeff and I came up with for the injectors and what we call a top hat. I will explain later.
The next step was face off both ends of the tank to make sure the end are straight and square. I used a steady rest for the long tube and chucked up inside the tube at the very end. Then I just used a cutting blade with vise-grips to hole the blade in place. I needed to do this since the outside of the tube is not perfectly round. So when cutting the blade tends to wander a bit making an uneven cut. Once this was complete I need to drill all the holes for the bolts to hold the closures on. Using #10-32 x 1/4 screws for the pressure including a 1.5 safety factor, I needed 22 holes drilled for each closure. Yes that is right 44 holes total. I also then had to tap each one of those holes. I sure am glad Don came over to help. He worked on the fin can while I drilled and tapped. This saved me some time. I then started work on the injectors. I drilled and tapped the holes on the CC closure for the injectors. I put the 3 outer injectors on a slight 2.5 degree slant towards the central injectors. I was going to use one 5/16th and three 1/4 inch U/C injectors, but I went with four 1/4 inch injectors after some last minutes changes and calculations.
I then had some 4 inch tubing (mailing tube) that I wanted to use for the grain liner. So I cut out about an inch and test fit the piece inside the combustion chamber tube. Then I epoxied the tube back together and placed it inside the combustion chamber tube so it would take the correct shape and set it aside to dry. Once it was dry I then did the other half of the tube giving my two liners for two grains.
We had some concern about the upper fiberglass tube and the shoulder height of the top tank closure. After talking with several people, I decided to glue a 10 inch tube coupler at the one end that will attach to the top of the tank. This meant I had to do a little more machining to shave down the outer edge to fit inside the tube coupler. It is much stiffer now and will be bolted with 4 shear bolts to help hold it in place. I also decided to use dual separation instead of single. So I needed the use shear bolts instead of steel.
The next item on the list was to make the nozzle. I had some 5 inch material from another project that was left over that I could use. So I chucked up the piece of graphite in the lathe and went to work. It took some time to make the nozzle with the boat tail and all, plus I had a big mess to clean up. Once the nozzle was complete I spent the next couple of hours cleaning up the garage. There was graphite dust everywhere. And yes I wore a respirator. After the garage was cleaned up I looked at what I had made. The nozzle came out great.
