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#11
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Quick Release Puzzle
if the action were not progressive, the discussion would intensify to lawyers lips levels
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#12
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Quick Release Puzzle
On 2/13/2014 7:31 PM, Joe Riel wrote:
There is one aspect of the design of a Campy quick release that I've never understood. The disassembled skewer consists of threaded rod with a cylindrical cap on the opposite end. The cap has a cross-bored hole. I believe the cap is coaxial with the rod. The axis of the cross-bored hole appears to be orthogonal to the axis of the cylinder, but offset slightly to one side. To operate properly, the "cam" of the lever (just an offset-cyliner) must be inserted so that, with the lever in the open positin, the lever points towards the side towards which the hole in the cap was offset. The offset is small and not readily noticeable, but if you insert the cam the wrong way, the lever doesn't work (it won't close). Can someone explain the purpose of the offset? Seems like to me that it could have been designed to be symmetric. Maybe I'm missing some subtle point. That's common to the design, not just Campagnolo. I have no idea why but it's nearly universal. -- Andrew Muzi www.yellowjersey.org/ Open every day since 1 April, 1971 |
#13
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Quick Release Puzzle
On Sunday, February 16, 2014 7:50:23 PM UTC-5, Phil W Lee wrote:
Frank Krygowski wrote: The hole is definitely non-circular, with the dimension perpendicular to the skewer being a bit larger than the dimension parallel to the skewer. I measure 0.280" parallel to the skewer, and 0.306" parallel. As you lock the QR by rotating the lever (and thus, the camshaft) the cam needs to be able to move to one side of the centreline of the skewer on it's way from bottom dead centre to top dead centre. When locked, the cam will ideally move just over-centre to provide security, but while unlocking, it will move in a semi-circle from it's closed position to it's open one - this means the hole must in some way allow the came to move to one side of the skewer centre line. It's not uncommon on devices intended to translate circular motion into linear. So it's essentially a Scotch yoke. http://en.wikipedia.org/wiki/Scotch_yoke But since it doesn't need to rotate 360 degrees, it doesn't need to be symmetrical. Right? BTW, am I the only one who hates the external cam QR's? I've always replaced any I have with the superior internal cam arrangement, with it's inherently lower frictional loss. The only reason I can think of for the external ones is to get around the original Campagnolo patent. I don't think it's the patent. I'll bet that expired long ago. The purported advantages I've heard of were lighter weight and lower manufacturing cost. I'd bet the real reason is just the cost, with the lighter weight being used to market it to those for whom only weight is important. I'll confess to using exactly one of those external cam QRs. It's used to hold my Carradice saddlebag onto the custom mounting brackets I made for it. I don't believe I'd trust one with a wheel. - Frank Krygowski |
#14
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Quick Release Puzzle
On Mon, 17 Feb 2014 03:57:35 +0000, Phil W Lee
wrote: I don't think it's the patent. I'll bet that expired long ago. Yes, I think it's a long time since that explanation had any validity, but it was a tale I heard some time back. According to various Campy history web pages, the patent was in 1933, which methinks is safely expired. I couldn't find the US patent. While Googling for the Campy patent, I did find: https://www.google.com/patents/US5653512 Fig 1 and 2 both show the elongated slot perpendicular to the skewer. There's no explanation for the slot in the text but there seems to be something that I can't decode under "Terminology cam". I think your explanation is the correct one (and certainly better than mine). Nor me, although I'm sure I've got one in use for something, somewhere. Ah, I have one on a handlebar clamp for an auxiliary light. Works ok for that. Looking around, I have an external cam on my Bike Planet light mount, one seat post QR, and a smartphone mount. They all slip, slide, and are difficult to adjust. The one's on the handlebars have a feature where they don't quite open when the tension is released, which is suppose to prevent accidental opening. All it does is make it difficult to remove when I lock the bicycle and go into a store. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#15
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Quick Release Puzzle
On 2/16/2014 6:50 PM, Phil W Lee wrote:
Frank Krygowski considered Thu, 13 Feb 2014 20:24:13 -0800 (PST) the perfect time to write: On Thursday, February 13, 2014 10:14:00 PM UTC-5, JoeRiel wrote: Frank Krygowski writes: I just took apart a Shimano QR and saw the same thing. The transverse hole in which the cam pivots (which is not circular, BTW) is offset by about 0.020". What is not circular, the hole or the cam? Presumably the latter, since a non-round hold wouldn't be cheap to make. The Campy cam is circular, but offset from the pivot axis. The hole it goes into, which is offset, is also circular. The hole is definitely non-circular, with the dimension perpendicular to the skewer being a bit larger than the dimension parallel to the skewer. I measure 0.280" parallel to the skewer, and 0.306" parallel. As you lock the QR by rotating the lever (and thus, the camshaft) the cam needs to be able to move to one side of the centreline of the skewer on it's way from bottom dead centre to top dead centre. When locked, the cam will ideally move just over-centre to provide security, but while unlocking, it will move in a semi-circle from it's closed position to it's open one - this means the hole must in some way allow the came to move to one side of the skewer centre line. It's not uncommon on devices intended to translate circular motion into linear. On very simple arrangements, you could allow the skewer to bend sideways as the cam rotated, but that would be rather a nasty arrangement. Instead, you simply machine out the hole to become a short slot, just long enough towards the side of the skewer head to allow the cam to move. For similar (but far more complex) arrangements, look at the valve-gear of a steam locomotive, and how the distance along the slot is used to regulate the amount of throw imparted by the cam (and through that, the proportion of the piston movement over which the valve is open to allow steam into the cylinder). BTW, am I the only one who hates the external cam QR's? I've always replaced any I have with the superior internal cam arrangement, with it's inherently lower frictional loss. The only reason I can think of for the external ones is to get around the original Campagnolo patent. Everyone hates them; they are detestable. That being said, some riders put up with them because they are light and cheap. Patents are long expired so I think cost is the driver here. -- Andrew Muzi www.yellowjersey.org/ Open every day since 1 April, 1971 |
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