[python] Re: New Jetrike Rev B Plans
- From: Rhisiart Gwilym <Rhisiart@xxxxxxxxxxxxxx>
- To: python@xxxxxxxxxxxxx
- Date: Sat, 13 Jan 2007 11:57:46 +0000
"....I found some engineering formulae to calculate the
bending moduli of square and round profiles....."
Siwmae 25hz,
The quote above from your conversation with Henry prompts a question:
Which is stronger? Obviously for tubing of identical width and
wall-thickness, the round will have less steel than the square, and
therefore be lighter. But what about relative strengths?
I too do 'seat-of-the-pants' building, designing everything in the
drawing office of the mind's eye for a long 'brooding' period before
ever I pick up saw or angle grinder; more than by any other method,
for everything that I make. Time consuming, and leading to a good
deal of trial, perceived error, and re-shaping once you do actually
start the physical making. Often I feel embarrassingly amateur and
ultra-slow, when I read how fast some of the professional engineers
on the list can turn out rideable bikes, from concept to riding down
the road. And showroom quality finish too, sometimes. But - well -
the artist's way sketched above is just amazingly pleasing in the
final results, both aesthetically and for engineering soundness. I do
all the furniture that I make by this method now, and I've even built
boats thus, up to 22 metres. Hairy at these sizes. There can be
panics along the way: "Oh Jesus, I've blown it! There's no way out of
this jam..." (There always is with steel, though; violent, murderous,
filthy - but wonderful - material!) But still, I'd never revert to
more orthodox techniques. Did you ever hear that quote from
Michelangelo Buonarotti, that he saw himself as 'releasing' his
sculptings from the raw block of stone, and never knew exactly what
he'd get to in the end. The Galeria in Firenze, where they now keep
his original 'David', also contains a number of his never-finished
pieces, where you can actually see the rough-surfaced figures
emerging from the blocks. At least with HPVs the amount of time,
materials and money invested is less frightening. And you can always
re-cannibalise.
I'm building one of my current bike projects using a spine made of
two round steel tubes welded in contact with stitch-welds at regular
intervals, over and under, like a Winchester rifle. I've used this
idea before on a much bigger scale, and it makes a beautifully
strong, rigid beam. Just curious to know if anyone has any
properly-competent-engineer's knowledge of the relative strengths of
this versus rectangular tubing? All professional information humbly
welcome.
Cofion, Rhisiart G
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