Stephen H wrote:so i would just need something steel with aprox the same volume ?... larry do you no the volume of the CC ??
Here's my calculation for the volume of the chamber:
The box is nominally 3.5 inches square with heavily rounded corners. I would NOT use a square box with sharp corners, because I believe the standing waves created inside would waste a lot of energy without contributing thrust. Here's what I get for the volume:
I estimate the interior flat-to-flat dimension as 3.38 inches. 3.38 x 3.38 gives us 11.42 in^2. Now, the corners take out about .75 inches on both sides of the corner -- ignoring the slight bulge for the curvature, that means TWO corners will take out a square of .75 x .75 = .56 in^2. Since there are four such corners, we subtract two squares: 11.42 - .56 - .56 = 10.3 in^2. That, then, is the approximate AREA of the side of the chamber.
I read the depth of the box, inside, as 1.45 inches, approximately. That means our chamber volume will be 10.3 x 1.45 = 14.94 in^3. This happens to be a reasonable approximation of the combustion chamber volume of the Dynajet, if you go from the front plate to about halfway down the nozzle skirt to the throat, which is why I liked the idea of using the box.
This is the type of electrical box that is used as a 'junction box' -- a place where a big circuit splits up into a bunch of smaller ones. It is also used in ceilings, where you need solid anchorage for a hanging fixture. Several kinds of cover plates are available, but what you want for our use here is a simple closed flat plate; if it has a little knock-out in the center, as mine did, you just weld it shut.
If it turns out that you MUST use a square box [because that's all you can get, for example], I strongly suggest you turn it on its corner, as I've shown in the Elektra II thread. That way, two of the flat sides will be working to strongly 'nozzle' the expanding gas flow into the tailpipe. Doing it that way will make more work, however, since  your exhaust port will have to be cut and filed in the CORNER of the box; and  you'll have to notch the pipe to fit the corner, instead of just using a square-cut end. However, none of this is thick steel, and if you have a good couple of files and a lot of stamina, it's not that tough as blacksmithing goes.
Don't forget that if you can't find a new box that's right, you might find one as junk, say at a building being torn down. A bit of surface rust won't matter. But, then you'd have some fair-size knockout holes to patch over, of course.
Best of luck!