Shadow Catcher wrote:Compass Rose is now 12 years old, the frame is all aluminum, unfortunately they did not use heavy enough aluminum for the tongue. The first one they built (and we owned) failed at the point where it goes under the body fortunately the second owner was going slowly and had it repaired. I had ours reinforced but was still concerned with too much flexing. During rebuild we moved the axel forward and again reinforced the tongue and no more flex.
The problem isn't the material, or even likely the thickness of the material, but the design (since a number of miles got put on the frame in the first place). There are welds right smack dab in the middle of the highest stress area of the tongue. So, you introduce both a stress concentration (where cracks like to start) and you lose most of the heat-treat of the aluminum in the weld heat affected zone. I would let the tongue pass under the first cross member and attach it with an angle which that had two fasteners in the frame and two in the tongue, but all of them going through the center of the respective beams. That way you don't lose the heat-treat, and you don't have a fastener going through a high stress area. Do that and the frame, if sized properly, will never have a fatigue failure. I think even better is to combine the frame and tongue into an A-frame, which potentially solves both of those problems.