This comment is interesting because it is exactly what Mike and I are currently discussing about these sprockets. In order to make them perfect enough to ensure every tooth on the new cog equally contacts every roller on the 1" pitch chain, we are testing and measuring very carefully, looking closely at them together on and off the bike to confirm 100% contact. So to have Bikes Guru's very true observations are timely in the vetting process. Mike wants to get them right or he won't offer them.
One more thing as important to remember here is that running a stretched, one inch pitch chain with his new cog will also result in tooth/roller contact on only one or two teeth at a time when
under power or braking. This
might wear the cogs' teeth quickly, especially if made of a softer metal.
My riding experience regarding modified cogs to work with 1" has been positive for the most part because the metal in the sturmey cog is so hard the teeth don't wear, even after a ton of miles. Ichi's are loud and cheap. When this new specially designed cog is run with a new chain it is sure to last forever. The cog I have been recently test-riding is a pre-production cog with an un~stretched Diamond chain and it is very, very quiet.
So look soon for the best alternative to all of the others....
Sounds like we're on the same wavelength here, and that's so cool you guys are putting in the necessary work to come out with a no-compromise cog design.
What CAD program are you working in? Or what file format can you work with and modify?
Maybe there's a way I can share my design files and the progress up to this point, and we can put our heads together on this.
I wouldn't want anything in return, other than a few 13t and 14t skip tooth cogs for my few bikes.
Here's a few pics of a really dialed-in prototype, which has the perfect amount of dish and recess for a Shimano 8-speed hub, and likely others.
It fits the hub like a glove, and the recesses clear all of the plastic covers perfectly (like a puzzle piece), while putting the chain line (back) in the most ideal position possible.
Take note of the weird 3 tooth cog in the photo below.
During testing, when I was doing chain wrap tests to determine if the tooth profile, spacing, and base circle diameter were correct, it occurred to me that I was getting a false reading, because every next tooth was a new starting point for the chain.
So the best solution I could come up with was to create a prototype with only the starting and ending tooth positions, as the chain wraps around the cog and heads back towards the front sprocket.
So in the photo diagram below, the black line (drill bit
on the left represents the chain entry, the black line on the right represents the chain exit.
When a chain roller is firmly at position 1, and then you tightly wrap the chain all the way around, when the chain roller that lands at position 2 is exactly meeting the tooth where it should, you know your tooth profile and base circle diameter are correct. All of the chain rollers in between will hit their tooth base correctly
An interesting finding during all of my design and prototyping... I collected every possible New Departure, Bendix, Morrow skip tooth cog I could get my hands on, mostly 12t, 13t, and even a few 14t.
The difference between a New Departure, and the Bendix or Morrow of equal tooth count, they used a different base circle diameter than each other, which could have been a design discrepancy, or wear in the stamping tooling, or?
Even more surprising, from an engineering standpoint, all of these stock skip two sprockets had a base circle diameter that was smaller than ideal, which may explain why (on many of the used cogs that I had) there was always such a deep indent from the driving force of the chain into the base of the tooth.
I was finding that the base circle diameters were too small, even for NOS or very lightly used chains. Which makes it really bad for the majority of the worn chains that most everybody's using.
And part of this is probably because the original designers were working with pencil and paper, while we are working with powerful, precision software that can magnify to a millionth of an inch.
On the prototypes below, disregard the technique that was used, where a small end mill created the three spines. It was the quickest way of prototyping these, and getting a sharp enough corner for the splines to engage The hub correctly.
In real life, this center hole and splines would probably be some type of broach or EDM or ?
Anyway, that's what I got
