New Motor, 3D Model

I'm working on making some animation to show how this motor goes together. I did a couple of cross sectional views that pretty much show just that. In the close up view you can see the nozzle and the insulation (the reddish colored stuff). The original version of this motor didn't use any insulation. With the short burn time and steel casing , it's really not necessary. I added insulation to this motor as the plan is to eventually epoxy fins directly to the casing in order to construct the rocket

2.375" Motor, Nozzle Update

I pretty much finished the nozzle. I used a parting tool to cut the o-ring groove and the groove where the insulation fits into. I then parted it off, flipped it, and cut the convergent side. I still need to drill and tap the retaining screw holes and I'm planning on adding some "gun blue" or similar rust resistant finish.

2.375" Nozzle Update

I finished the back cut on the shoulder area. In an attempt to get really clean flow into the throat area, the convergent starts at a steep 45 degrees that leads into a shallower 22.5 degree section leading into the throat. This can be clearly seen on the back of the convergent side in the photo. I also chose a shallower divergence than the "standard" 12 degrees. A couple more hours and I should have a finished nozzle.

2.375" Motor, Nozzle Progress

I'm making pretty good progress on the nozzle. The black line in the top few photos is about where it'll get parted off. I still need to cut the 0-ring and insulation grooves, do the back cut behind the shoulder, and index the retaining screw locations. Then I'll part it off, flip it over, and finish the convergent side.

2.375" Motor, Starting Nozzle

I managed to start the nozzle. I'm starting with 2.75" diameter stock which is less than ideal; I would prefer to start with some thing closer to the OD of the finished part, but it's what I have on hand. It shouldn't be too bad though since I added a new, larger motor to the lathe a while back. I've only done some light turning with the new motor, so I can't wait to find out how aggressive a cut it'll handle. The starting piece is about an inch and a half longer than the finished part will be and weighs nearly nine pounds. I would guess that the finished nozzle will come in at around 1/2 lb. The general plan is to machine the divergent section, throat, shoulder, and index the retaining screw locations. Then part off the nozzle, flip it, and finish the convergent side

2.375" Motor Casing Completed

I finished the casing for the motor. I realized that I made a mistake in the CAD drawing that I posted earlier today. There should be six retaining screws for both the nozzle and the bulkhead versus twelve. I also made a slight change to the length of the casing, opting to make it 3/4"shorter which allowed me to true the ends on the lathe. I hadn't planned on being able to do that but by turning the tool post backwards I was able to extend it's capacity by just enough. Since just a very light cut was needed this worked fine. The design is pretty generous in the propellant segment spacing, so I'll make up the deficit by reducing the spacing slightly.

The bottom photo shows the new extended casing next to the older motor design. The new casing still has it's rust preventive zinc coating. The coating doesn't add any structural strength and has a fairly low melting point so I'll remove it with a quick dip in some muriatic acid.

2.375" Motor, Completed CAD (nearly)

I'll need a few more dimensions, but I'm pretty much ready to start. I'll start with the casing , then I'll be able to determine exactly what the OD of the nozzle and bulkhead needs to be.