When ramming the clay and fuel into the engine during assembly, it creates a lot of outward forces that have a tendency to damage the cardboard tubes. In order to abate this problem, you surround the cardboard tube with a casing retainer that will take up some of that force and prevent the tubes from deforming or bursting. This can be done with either plastic or steel, but steel allows you to use fewer clamping bolts due to rigidity so I went with that. The fabrication process basically starts with a schedule 40 steel pipe, which is cleaned up and slit down the middle with a slitting saw on the mill. Then a flange is machined and welded in place. The only really tricky part of this is that you need to be VERY careful not to overheat and warp the part when welding. The easiest way to accomplish this is to simply go very slowly, welding about an inch at a time and then giving the part time for the heat to equalize and cool a bit. Seems like everything went pretty smoothly, though for the large retainer the flange warped a tiny bit, which reduces it’s clamping range somewhat. Shouldn’t be too hard to account for this, and i can easily make another in the future if it becomes bothersome.
