The steel tube with thin 0.25 mm walls flexes less than aluminium tube with 2 mm walls. While the 1st mode resonance @ 260 Hz is only about 0.05 g
lower, the second and third harmonics are completely gone.
But the high rigidity of steel brings a different problem. While the damping capacity η
of stainless steel is more or less the same as the aluminium alloy that we use (about 4-6), there is a lot less steel to do the damping! As a result, counterweight resonance shoots right up, and is now the dominant resonance of our arm. The counterweight stub is a solid aluminium rod, ringing with a very high Q peak.