Track cogs FYI

[geoffs]

I knew that i had read a bit about the difference between the threads on stamped and machined cogs and I just found it.
Tech note is from the Phil Wood web site.
Tech Notes – Cog Recommendations / Cautions

· The use of “stamped” or plated cogs with minimum thread engagement and beyond the normal spec on thread tolerances are not recommended with quality track hubs. The use of thick cogs should be avoided, as this will limit the important engagement of the lockring. There is an optimum balance between the amount of thread on the cog and the lockring. Deviation from this balance will result in stripped threads on the hub of either or both.

Tech Notes – Cog Thread Cautions & Cog Material
· Track hubs have short thread width for the cogs. Binding may not be as apparent on the track hub as on a Phil freewheel hub. What occurs is the leading and trailing thread on the cog is binding on the hub thread. The high stress of sprinting could shear the top of the thread form at the binding points. The cog slips and binds on fresh thread forms, and so on, until all thread forms have collapsed / stripped. A compatible hub/cog thread will offer over 32” of shear contact. Mismatched thread will offer about 4”.

I found this previously when i was researching why I had spun the cog off the thread on my fixie riding up the ramp onto Anzac Bridge.