I am trying to reduce the weight of an aluminium tube, 3mm thick, 4.5 inches in diameter and 4.4 metres long.
It is necessary that the tube will not twist or bend and my first thoughts are to bore innumerable holes or make slits.
The tube is for a Conservatory sunshade, the last one was wooden and lasted 25 years but I hope that this one will see me out. I am 84 and can easily lift the tube but would prefer to reduce the weight.
To limit the risk of breakage due to bending, place the holes working from both ends, up to around one third distance from the end, assuming that your rod is end supported only in which case the maximum bending stress are concentrated at the centre of the bar when under load and the stress proportionally decrease from the centers and becoming zero at the any support point.
The device is just a very large roller blind which is put up in the Spring and taken down in the Autumn.
The original was constructed like a 20s model aircraft fuselage.14ftX 4.5 inches. It was strong and light and rigid after all those years it needed replacing and I could not face all the woodwork so that is why I went for aluminium.
I did look at other materials but this was the only one that has the correct characteristics - my only worry is the weight. Tomorrow I will try to establish the actual weight difference using the bathroom scales.
The wooden rail would be far too heavy hence the "fuselage" construction.
Thank you for that information, it will come in useful if weight reduction becomes necessary.
... just seen on TV tonight, a space-station astronaut, who was demonstrating the use of a small rotating hand crank-lever to initiate an experiment for the camera ... it [the lever] was full of big drilled-out-holes to minimise it's weight to get it into orbit ... less fuel required.
Aitchbee, odd as it my seem the correct sized holes drilled in the right places can actually make a steel beam stronger hence the construction used in steel bridges etc, it is to do with the distribution of stresses as I recall from my years at Tech College. In OP,s case if it only needs lifting up and taking down once a year I would get some assistance rather than start drilling holes in it.
The project is now complete.
I took namtas's advice and removed 32 X 10"X 1" pieces leaving about 20" clear at each end and in the middle and spaced the slots evenly. About 13% reduction in weight which I thought was worth it. In the end I think that I could have cut more slots and still maintained the required strength.
Yesterday my two tame professional engineers admired the work (with tongue in cheek) and put it up in two shakes. Works a charm, I should have done it 24 years ago.