Looks great - I wonder if the muffler clamp / woodruff key setup could be duplicated on a small bolt cutter instead of the vice grips. That would have more leverage if it could be done and probably much quicker and easier on the hands. It would need just a touch more fabrication, but if you could cut or grind down the size of the cutter head to fit inside the tubing and you use one of the smaller bolt cutters it should work pretty good, no?
