2024 is certainly a good choice and I for one would not thread the end cap(fill adapter) and use 4 retention screws and of course Id anodize it and use a MDS hammer to prevent galling. Like Bob already stated you would need almost perfect screw retention for the valve also so Like the end cap I would add a 4th retention screw. I know it sounds like overkill but one can never be to safe. I think its a great Idea Matt if carried out with safety in the foremost thought. Ill be watching and subscribed.
Lloyd Sikes recently sent me a copy of his latest tubing strength calculator spreadsheet.... Using 50 Ksi yield and 70 Ksi tensile (UTS) for the 2024-T3 tubing, and assuming 1.25" OD x 0.095" wall, I get a yield pressure of 8,170 psi and a pressure to burst of 11,438 psi.... That works out to Safety Factors of 2.7:1 (yield) and 3.8:1 (UTS) at 3,000 psi.... The ASME requirements for pressure vessels are a minimum of 3.5:1 to burst, and 1.5:1 yield, although the latter is worst case scenario, after nearly infinite fatigue cycles.... Lloyd and I decided on 2.5:1 minimum to yield, providing the tensile is over 3.5:1.... 2024-T3 has pretty good resistance to fatigue, providing the stress is less than half the yield point, so at 2.7:1 that tube should be safe for a VERY long time.... The standard Mrod fill fitting threads, which are 1.125"-24 TPI should be OK, providing they are cut properly, since the tube must be bored out to 1.083" to cut them (it starts at 1.060").... The remaining wall thickness, above the thread root, and assuming the OD is on spec. at 1.250", is 0.083", and providing the O-rings seal inside that, where the tube is full 0.095" wall thickness, that area is only subject to an axial load of 2,647 lbs. at 3000 psi.... Its safety factors to resist that axial load are 4.1:1 (yield) and 5.7:1 (UTS), which is greater than the SF for the hoop stress on the tube.... Thread shear strength should not be an issue with the stock thread engagement.... The stock MRod valve retention screws work fine, the only thing that is different is the bearing strength of the screw heads in the aluminum tube instead of steel.... 2024-T3 has a higher compressive strength than its yield or tensile, at 76 Ksi.... and based on the three 10-32 screw heads equally loaded in the tube (ie the holes are drilled accurately, so that all three screws have equal load) the safety factor to yield is 2.5:1.... This is the most highly stressed of all the safety factors, so keeping an eye on the tube for any distortion around the screw heads SHOULD be the first indication that you have a potential problem.... Please remember, I am NOT an Engineer, but Lloyd and I spent a lot of time refining his spreadsheet, and checking the ASME requirements.... and I personally trust it.... The reason I have all these figures handy is that I also plan on using a 2024-T3 pressure tube with an MRod valve, fill fitting, and hammer in a future build.... I have every confidence in it.... but I am NOT saying you should take that as a guarantee of the safety of this decision.... Improper machining, or out of spec. threads, would be of great concern, of course, when working with a 3,000 psi MSWP.... and it would be a good idea to buy certified tubing, or at least tube where you know the wall thickness is within tolerances....Bob
unless using a nylon hammer should galling and abrasion be expected from hard material(hammer) rubbing on softer ?
i'd even anodize the inside. from what i'm reading t3 is pretty suseptable to corrosion. there are different coatings and anodizing available.
It certainly would change the Mrod's weight many curse, but not my cup of tea currently. I do wish you the safest of luck though in your quest on this.