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Ideas on how this was fabricated ?
The following pics are of a bicycle crank arm, manufactured in
reaonably small quantities around 20 years ago. What makes them different is their shape. Made of Chromoly steel, hollow with no visible seams. hexaganol cross section, tapering from one end to the other in 2 dimensions (one is obvious, the other is widthwise end to end - wide end at crank spindle, narrow at pedal) http://users.fcpl.com/~ben/aero/crank1.jpg http://users.fcpl.com/~ben/aero/crank2.jpg http://users.fcpl.com/~ben/aero/crank3.jpg http://users.fcpl.com/~ben/aero/crank4.jpg http://users.fcpl.com/~ben/aero/crank5.jpg http://users.fcpl.com/~ben/aero/crank6.jpg http://users.fcpl.com/~ben/aero/crank7.jpg http://users.fcpl.com/~ben/aero/crank8.jpg Suggestions so far are : 1. 2 Halves Stamped from sheet steel, welded together and then finished. 2. A Custom tube - drawn and tapered to exact requirements, with ends formed together in a tool, brazed and finished. The trouble with 1 is that I can's see any evidence of the weld - the 'seam' between the two halves is absolutely 100% - straight and sharp. The rest of the visible welding though is not so good, so I am not convinced by this. No. 2 seems possible, particularly given that the ends (where the 'seam' betweenm the two halves are) looks definitely 'manually' finished (not absolutely straight and true). But, I can't see how tubing can be shaped hexagonally and then tapered in this way. Any light anyone could shed would be very welcome! Thanks. BJS |
(Ben) wrote in
om: The following pics are of a bicycle crank arm, manufactured in reaonably small quantities around 20 years ago. What makes them different is their shape. Made of Chromoly steel, hollow with no visible seams. hexaganol cross section, tapering from one end to the other in 2 dimensions (one is obvious, the other is widthwise end to end - wide end at crank spindle, narrow at pedal) http://users.fcpl.com/~ben/aero/crank1.jpg http://users.fcpl.com/~ben/aero/crank2.jpg http://users.fcpl.com/~ben/aero/crank3.jpg http://users.fcpl.com/~ben/aero/crank4.jpg http://users.fcpl.com/~ben/aero/crank5.jpg http://users.fcpl.com/~ben/aero/crank6.jpg http://users.fcpl.com/~ben/aero/crank7.jpg http://users.fcpl.com/~ben/aero/crank8.jpg Suggestions so far are : 1. 2 Halves Stamped from sheet steel, welded together and then finished. 2. A Custom tube - drawn and tapered to exact requirements, with ends formed together in a tool, brazed and finished. The trouble with 1 is that I can's see any evidence of the weld - the 'seam' between the two halves is absolutely 100% - straight and sharp. The rest of the visible welding though is not so good, so I am not convinced by this. No. 2 seems possible, particularly given that the ends (where the 'seam' betweenm the two halves are) looks definitely 'manually' finished (not absolutely straight and true). But, I can't see how tubing can be shaped hexagonally and then tapered in this way. Any light anyone could shed would be very welcome! Thanks. BJS Made in 2 halves, welded, finish machined, tis why the edges are so straight, but the ends (radius) are not. The only other option, was it was cast, then machined. -- Anthony You can't 'idiot proof' anything....every time you try, they just make better idiots. Remove sp to reply via email |
On 13 Jan 2005 14:55:07 -0800, (Ben) wrote:
The following pics are of a bicycle crank arm, manufactured in reaonably small quantities around 20 years ago. What makes them different is their shape. Made of Chromoly steel, hollow with no visible seams. hexaganol cross section, tapering from one end to the other in 2 dimensions (one is obvious, the other is widthwise end to end - wide end at crank spindle, narrow at pedal) http://users.fcpl.com/~ben/aero/crank1.jpg http://users.fcpl.com/~ben/aero/crank2.jpg http://users.fcpl.com/~ben/aero/crank3.jpg http://users.fcpl.com/~ben/aero/crank4.jpg http://users.fcpl.com/~ben/aero/crank5.jpg http://users.fcpl.com/~ben/aero/crank6.jpg http://users.fcpl.com/~ben/aero/crank7.jpg http://users.fcpl.com/~ben/aero/crank8.jpg Suggestions so far are : 1. 2 Halves Stamped from sheet steel, welded together and then finished. 2. A Custom tube - drawn and tapered to exact requirements, with ends formed together in a tool, brazed and finished. The trouble with 1 is that I can's see any evidence of the weld - the 'seam' between the two halves is absolutely 100% - straight and sharp. The rest of the visible welding though is not so good, so I am not convinced by this. It's a lot easier to make and finish a nice outside weld than it is a fillet weld like the gobby-looking ones. The halves may also have been resistance-welded like some tubing is made from rolled flatstock. |
"Don Foreman" wrote in message
... On 13 Jan 2005 14:55:07 -0800, (Ben) wrote: The following pics are of a bicycle crank arm, manufactured in reaonably small quantities around 20 years ago. What makes them different is their shape. Made of Chromoly steel, hollow with no visible seams. hexaganol cross section, tapering from one end to the other in 2 dimensions (one is obvious, the other is widthwise end to end - wide end at crank spindle, narrow at pedal) http://users.fcpl.com/~ben/aero/crank1.jpg http://users.fcpl.com/~ben/aero/crank2.jpg http://users.fcpl.com/~ben/aero/crank3.jpg http://users.fcpl.com/~ben/aero/crank4.jpg http://users.fcpl.com/~ben/aero/crank5.jpg http://users.fcpl.com/~ben/aero/crank6.jpg http://users.fcpl.com/~ben/aero/crank7.jpg http://users.fcpl.com/~ben/aero/crank8.jpg Suggestions so far are : 1. 2 Halves Stamped from sheet steel, welded together and then finished. 2. A Custom tube - drawn and tapered to exact requirements, with ends formed together in a tool, brazed and finished. The trouble with 1 is that I can's see any evidence of the weld - the 'seam' between the two halves is absolutely 100% - straight and sharp. The rest of the visible welding though is not so good, so I am not convinced by this. It's a lot easier to make and finish a nice outside weld than it is a fillet weld like the gobby-looking ones. The halves may also have been resistance-welded like some tubing is made from rolled flatstock. Man, that's an interesting one. I suppose that none of those three bosses would let you look inside with a borescope, huh? The small one that apparently fits a drive-pin on the chainwheel probably goes all the way through, too, like the ones on the ends? If it *does* open to the inside, you could find an inspection shop that has a small, flexible borescope, and you'd probably be able to see where the seam(s) is with that. Or you could just take a hacksaw and cut it in half for a look. g -- Ed Huntress |
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