BULKHEAD PRESSURE FITTINGS:
Push connect fitting, non-return valve and Quick Disconnect fitted to the oxidizer bulkhead. We had to make and extension for the NPT tap as it is tapped from the inside of the one piece bulkhead. Official max pressure of the push connect fitting is approx 40bar but the fitting held when tested to Nox tank pressure.. Burst pressure of the 6x4 PA hose is 80bar.

SERVO BALL VALVE:
Stainless steel ¼” NPT ball valve, PN63, from Aliexpress, getting the HalfCat recommended high pressure ball valve from McMaster was nearly impossible or came down to EUR 80,- per valve. Customized the STL a bit as the ball valves where slightly larger and did not fit. We also made a new lever and connection print to make it all work.

THRUST STRUCTURE FIN BRACKETS:
Thurst chamber assembly / Tank interface composed of 25x25x3mm auminium angle bar for fin brackets. We thinned the bracket to tank spacers a bit and added holes for the M6 bolts. The thrust chamber mounting brackets were made of 25x38x3mm aluminium angle bar and machined with a radius of 32,75mm to fit around th nozzle, thereby also aiding in alignment.

DOWN COMER AND FLEXIBLE HOSE:
A straight fitting AN6 hose kit was purchased from Aliexpress. The kit contained stainless steel braided PTFE hose, straight fittings and can be cut to length. AN6 has an ID of approx 8mm, sufficient for the Mojave Sphinx and room for some future upgrades. For those wondering why the ESTES igniter motor is so high up, please see the photo, its to create some clearance between the Nox line and the igniter body.

Tank bulkheads:
After machining the original bulkheads we saw the improvement of the one piece bulkhead as done on the excellent Sinnoh Sphinx+ build. We quickly realized the dual o-ring design was more in line with our previous rocket motor builds and were happy to adopt the upgrade in the NITROCAT as we didn’t machine the retaining rings yet (which we would have modified by using a 100x10mm tube with integrated threads so it would not use the 3d printed nut retaining ring). Machining the internal bore of 90mm deep proved quite the challenge with the stringy aluminium not clearing the bore. We got it done by frequently stopping the machine and manually removing the bird nest. We are not giving up and ordered a PCD insert with chipbreaker which hopefully help us breaking a chip at moderate feeds and speeds. Through tool coolant would have helped a lot but not available on our machine. We changed to 12x M6mm bolts for retaining the bulkheads in the thin walled 100x3mm casing, more on this later. Dual o-rings 86x4mm NBR 70 were used to seal the tank. We are very please with the fit and it seems to be a big improvement on both the oxidizer as well as the fuel side of the tank. Does any catch the crash (e-stop to the rescue) in the toolpath picture?

Piston:
No significant changes but modified to accept the same metric o-rings 86x4mm NBR 70 as the bulkheads.

Nozzle & Thrust chamber:
We simplified the outside of the nozzle contour for ease of manufacturing on a manual lathe. The 40mm copper insert was pressed fitted into the nozzle therefore removing the need for a garter spring. The 25m throat, as well as the convergent and divergent sections, were machined afterwards.
The thrust chamber was made from a 80x15mm tube and machined down to an OD of 76mm with an ID of 50mm. Injector recess ID 65mm.

Injector & Flanges:
Following closely the MS standard design but modified to receive a 65mm shaft retaining ring and dual 60X2.5mm NBR 70 O-rings. Oxidizer holes: 6x 2,5mm; fuel holes 6x 1,9mm. AN6 fittings and a pressure sensor to measure chamber pressure. There are questions on the use of NPT but the MS designers were right on selecting this NPT thread. We had our doubts as well but it proved to be the right choice for this design. Good for blind holes in the injector, also for aligning and the avaiability of cheap connectors i.e. the NPT --> AN6.
The flanges were ordered at a local shop which had a nice webshop wizard to create custom flanges – no need for uploading drawings / .dxf’s. OD 100mm, ID 65,5mm, PCD 84mm; 8x 6.5mm holes made from 6mm thick steel plate. Test fit of the thrust chamber went OK. Used an oversized 82x43mm grafite gasket with st.st. inlay which was cut to the required dimensions between 2 discs. Threaded rods are M6.