I Under stand what you are trying do. It seems you are thinking this out pretty good. But I am don't know what your thought process is so, I have some questions.
If you have the ability to machine a spherical end on the chamber, why don't do the mouth of the chamber spherical also?
I don't like the placement of the vent. Why are you not doing the conventional system?
How are you going to attach the trunnions?
The design of the powder chamber was copied off of something I saw on one of the posts in the forum right down to the conical profile though I had wanted to ask if a cylindrical straight sided chamber would work just as good. I hadn't thought about making the bottom of the chamber spherical because I hadn't seen it done by others. I think I got the basic dimensions from a gomer chamber I saw that told me that it needed to have a minimum of 1 caliber thickness all around.
But then I read an article a while back about the handgonne and it showed a very deep powder chamber like a 10x depth to it's caliber and I believe it said that the deeper it was the better the chamber worked.
On the vent placement, that's just the easiest most direct way to get fuse to powder. The diagrams I've seen on the forum have shown the vent coming in at an angle and that would require drilling into the O2 tank and the powder chamber and would require it to be welded into place and I've read that any weld should be avoided when possible due to the micropores inherent in all welds getting contaminates blasted into them and that there's no way to clean that: end result a corrosion weakness will eventually compromise the tube.
Same deal with the idea of making the powder chamber removable, easy to pull apart to clean and no welds.
I had assumed that the only reason to have the vent come in from the side was that's the "traditional" place to have it for historical purposes and that it really wouldn't matter where it was located and since I already have holes through the base of the O2 tank and I need a connection point right there it was just the natural place to put it. I'm not overly concerned on making this an exact replica of a civil war mortar.
Also, the stub on the end of the helium tank only appears to be there to have a lift point on each end. Or perhaps it's there for it to sit in a rack and only be supported at the two ends. This tank had been used in a lab doing superconductor research and maybe they had it heavily insulated? In any event after looking at the inside of the tank I see that I can cut that off which would shorten the vent by 2.5". Looking as my drawings I see that with that stub gone going straight up the back side would be the shortest path to the exterior.
However, I'm all ears to your concerns. What worries you about this orientation of the vent?
It had also occurred to me that I could set a pair of electrodes in epoxy through the connecting rod and then have a capacitor deliver enough juice to make it jump the exposed gap where they came out in the powder chamber, a sort of home made spark plug. I'm an old ham radio operator and so I'm all up on spark gaps
I'm N5NCV in case there's any op's in the forum.
On the trunnions I'm planning on using the discarded end of the O2 tank to make them. I'll cut off two sections about 10" long and then cut the profile of the side of the helium tank into one end of the harvested section so that it sits flush. It's high strength 1/4" steel and should hold the shear force from firing. Figured I'd do a really deep weld on the inside of the trunnion and then go around with a mig and fill up the seam that will be visible on the exterior and then grind the external welds down with the idea of trying to make it look like the whole assembly was cast rather than welded up. Then I'll cap the end with plate and weld that on and grind down flush. If ya'll think this construction method might be weak I could take a piece of 1" x 8.75" flat bar and place it inside the trunnion oriented to be in line with the recoil force to beef it up.
9" trunnions look like the right scale for this size mortar. Aside from collecting a lot of photo's of carriages I haven't started designing that yet. I have about a hundred standing dead oak tree's from last summers drought here in Tx and know someone who has a mini saw mill who'll cut whatever sizes of timbers I want but that's about all the thought I've given to what I'm going to mount this on.
