I'm building a rocket motor to compete at the 2007 xprize cup. During my last testing session It ran 106 seconds with not damage, but some of my seals leaked. My post on the problem with video clips:
While its not shown well on the linked drawing there are 10 screws spaced evenly around the motor holding the bottom end in. After disassembling the motor I determined that the o-ring had little notches ligned up with the screw holes, so the oring extruded into the screw hole openings on assembly and was damaged.
I'm rebuilding the asssembly and I was thinking that I could retain the bottom end with an external screw cap so the oring never saw anything but smooth metal.
This is a long way of getting to my question:
I have a 0.125 inch thick aluminum tube 2.5" OD. I want to make a threaded aluminum cap that threads over the outside to retian my copper throat. I can't have more than 0.24 inches of thread or it interpheres with my fuel feed lines. The aluminum tube is fuel cooled so it will stay cool, less than 100C.
What thread depth and TPI would you reccomend for maximum strength? This will see as much as 1200 lbs of contininous force with possible shock loads on a hard start of 2X that.