Details zu Lochkreismustern bei Kettenblättern: Unterschied zwischen den Versionen

* [[Elliptisches Kettenblatt|Elliptische Kettenblätter]] funktionieren am besten in verschiedenen Orientierungen. Bei einem [[Liegerad]] ist möglicherweise diese Orientierung anders. Viele elliptische Kettenblätter funktionieren genau entgegengesetzt zu den klassischen [[Shimano Biopace]] Kettenblättern (siehe [[Shimano Biopace ® Kettenblätter]]).  

 

*   Pins and ramps involve some compromises. Though teeth may align multiple times around a pair of chainrings, shifting is best near the dead centers of crank rotation, to minimize stress on the front derailer and disruption of pedaling cadence. To meet these criteria, there can be only two sets of pins and ramps opposite each other, and chainrings must differ by a multiple of two teeth. This requirement is met, for example, by a 52-36 or 50-34 racing double pair of chainrings. Chainrings with preferred orientations for shifting cannot be rotated on the crank spider during overhauls to increase wear life. It is conceivable that this problem could be solved using threaded pins that can be removed and reinstalled, but I don't know of any manufacturer offering this feature.

Introducing a novel bolt pattern is easier than it once was .Chainrings used to be stamped out in a huge punch-press machine, like cookies with a cookie cutter, then lightly milled to reduce the thickness of the teeth and to drill mounting holes. Teeth of a 1X chainringA large number of chainrings had to be produced in each size to justify the tooling cost, but unit cost was low. Now, on the other hand, anyone with computer-aided design software and a computer-aided milling machine can establish a new bolt pattern at low cost -- but the unit cost is higher.

The popularity of multi-speed 1X ("one-by") systems -- those without a front derailer -- also has led to innovation. In a 1X system, the wider space between the outer plates of a chain lets every second chainring tooth be wider, offering some advantage in preventing the chain from coming off, and in the wear on the sides of teeth being taken by twice as many teeth. There is no additional bearing area for chain tension though, as the rollers of the chain have to fit between the inner plates. Chainrings with wide-narrow teeth are possible only with even numbers of teeth, and are practical only in a 1X system, because a chain could land the wrong way when shifted.

All in all though,fewer bolt patterns are currently made the early 21st century than in the mid-to late 20th century, as many legendary manufacturers have dropped out of the market, been bought up, or adopted bolt hole patterns from the largest manufacturers.

I started my work reviewing the bolt-circle diameter table by reviewing the entries with known bolt-circle diameters and evenly-spaced holes. Their spacing can be determined with trigonometry. I found small errors in published distances on our list and in other references. Evidently, people had taken measurements and never checked them with math. I corrected errors where I found them.

For uneven patterns, measurement and calculation are more complicated. Buying a sample of every kind of chainring would have bankrupted me. So, for some chainrings, I had to use manufacturers' specifications, or reverse-engineer geometric constructions from manufacturers' photos. This is trickier. How can it be done?

 

While bolt-circle diameters vary, the geometry of the tooth circle of all round bicycle chainrings adheres to a fixed pattern, as the pitch of the chain and the diameter of its rollers are the same. The tops of teeth may stand at different heights, but the gaps between teeth are at the same diameter, within tight tolerances, for any chainring with the same number of teeth. The diameter between gaps opposite one another may be calculated based on the dimensional standards, and he correctness of the calculation may be confirmed by measuring an actual chainring with an even number of teeth. I did both and checked with a 1982 Japanese Industrial Standards manual. You may find my calculations in the Microsoft Excel workbook here. And here is the page from the JIS manual.

 

==Wie man Lochkreismaße berechnet==

To find the bolt-circle dimensions of a chainring, I copy the manufacturer's photo of it onto a letter-size sheet of paper, as large as I can make it. To confirm that the plane of the camera sensor was parallel to that of the chainring, I find the center -- the intersection of two lines between opposite points on the chainring. This is easy if the chainring has an even number of teeth. Placing a straightedge at the edge of opposing teeth makes for high accuracy. Then I measure the distance out to the bolt holes from the center. If the camera sensor and chainring plane were parallel, radial distances will be the same. Most chainrings have all bolt holes at the same radius, making it possible to take an average. If the differences among measured radii are at all substantial, I reject the photo.

Having confirmed that a photo is usable, I draw the polygon connecting the centers of the bolt holes, and measure the lengths of the sides. For the sake of accuracy, I measure from right side to right side or left side to left side of holes, not between the centers.

If the manufacturer has not given the bolt-circle diameter, I need to determine it. Having established the diameter at gaps between teeth in the photo, I also measure the radial distance inward from the bottom of a gap between teeth to the center of a bolt hole. The ratio between the measurement in the photo and the calculated dimension establishes the scale of the photo. The image below gives an example of this geometric construction.

The bolt circle diameter at the scale of the photo is the distance between gaps, minus twice the radial distance from a gap to the center of a bolt hole. I determine the bolt-circle diameter by multiplying by the ratio of actual spacing between gaps to the one in the photo.

The image below shows my measurements of a photo of a Wolf Tooth CAMO series chainring, which has subtly uneven bolt-hole spacing. I calculated the bolt-circle diameter and angles of the bolt holes based on measurements like the ones shown, using photos of several CAMO chainrings on the Wolf Tooth Web site.

Having done this for several chainrings with the same bolt-hole pattern, I can take an average, and then make an adjustment based on the probability that bolt holes are spaced at integer numbers of degrees from one another.

 

I sent results to Wolf Tooth and received confirmation that they were correct, validating my method and allowing me to trust it as I applied it to other chainrings. I found a few measurements of other chainrings with unevenly-spaced bolt holes on the Wolf Tooth site which further confirmed my measurements.

If the manufacturer has given the bolt-circle diameter, the task of measurement is easier. The scale of the photo can be determined directly from the radii from the center to the bolt holes. The FSA chainring in the photos below is clearly marked as having a 110mm bolt-circle diameter.

Results of these calculations are on the bolt-circle diameter cribsheet page and in the templates which my son Jacob has generated. You can print out the templates to check chainring dimensions.