For added security, use some lochtite on the nuts or use 2 nuts tightened against each other. The swiveling action could loosen the bolts.I made similar and I added epoxy resin about half way up each tube for extra weight. Just be sure to add the same to each tube to keep them balanced. I used scales when adding the resin.
Great idea. Could be expanded on too. Imagine a tool mounted to a clamp over your work. Kinda like a surface grinder.
Love it ?