I have a 5' long, 2" diameter piece of aluminum round bar. I want to make it at least 30% lighter, while preserving as much rigidity as possible. (The force I'm most concerned about is torsion, so if this is too broad then please substitute torsional rigidity.) While I want the rod to be at least 30% lighter, I'm ultimately after find the best ratio of strength to weight. I have an incredible machine shop that allows me to drill as many holes as desired in any diameter down to 1/16". What pattern of holes should I drill?

  • $\begingroup$ do you want the holes drilled across the diameter or in the middle like a pipe? Transverse plane can mean either, and vertical isn't useful unless we know the orientation. $\endgroup$
    – Tiger Guy
    Sep 13 at 5:44
  • $\begingroup$ From top to bottom, like a pipe. What's a better way to describe that direction? Axial? Along the long axis? $\endgroup$
    – Jim
    Sep 13 at 13:52

1 Answer 1


An axial hole.

That is why prop shafts on cars and trucks are hollow.

Even the transmission shafts between tractor to device, driven by the pto (power take off) are also hollow. Some are not round, used to be square then round and now a lemon shape is common.


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