What is the optimal support angle for a steel clothing rack?

[DaveC426913]

I was able to find a paper determining the Elastic Modulus for commercial wooden dowels, which the critical material property for determining the deflection of beams; and, unfortunately, wood has a modulus that is only 10% of that for SST, which, in simple terms means that the wooden dowel insert is much to flexible to add any stiffness and support to your SST tubes. For example, replacing the SST tube on the bar with a solid 1" dowel results in a center deflection in the bar of 2.75", so if overloaded the SST tube would buckle under the load long before the wooden dowel would add any support.

Hm. I see your point. I had been assuming that the dowel would preserve the rigidity of the tube, like filling a hollow pipe with sand prior to bending it will prevent a buckle.

 

[Merlin3189]

Vertical pole is about 66" high, 1" O.D. 1/16th" gauge.
If that's not strong enough in either vertical or horizontal, I run a thick dowel up the centre of the tube.

I don't think adding wooden dowel in the centre would add a lot to the stiffness. Most stress is carried by the edge of the cylinder and the stress/strain modulus of wood is lower than steel. The wood would help resist buckling, but we hope you will be well away from that risk.
One suggestion for strengthening the round tube (other than bigger diameter and/or thicker tube) is to locally reinforce the tube at the strain peaks by sliding another tube over . I haven't done any calculations on that yet, but I've seen it used to strengthen tent ridge poles.

An alternative might be to use a square section instead of circular. My estimate of stiffness for 1"sq tube vs 1"diam cylinder is the square is about 5x as stiff, but only 30% heavier (but check that. I haven't done the full sums on square tubes yet.)

I defer to anything JBA might say, but I get a deflection of about 1.25" max on the vertical and about 0.125" on the horizontal with uniform (1.3 lb/") load and support at 42.5". (I now get that as optimum for uniform load. Though if the load is likely to be biased towards the hinge, 40" might still be better.)