The Mysteries of Chain-Link Connectors

Published on: 09:40AM Dec 16, 2012

Today's blog is about one of the  small, insignificant, trivial things I fret about when assembling machinery.

When connecting master links in roller chains, there are ways that are logically correct and ways that are logically incorrect. It makes sense to install the retaining clip on a master link so the "open" end is away from the direction of the chain's travel. Motion of the chain and any contact with idler blocks or other components will then force the clip tighter, rather than knock it loose. Logical.

I've yet to find or figure out such a logical explanation for how to install the cotter key in a half-link. If the cotter key is installed with its head in the direction of chain travel, motion tends to force the cotter key tighter into the hole in the half-link's pin (which is good), but contact with idler blocks, etc. threatens to uncrimp the tails of that cotter key (which could be bad). However, if the key is installed with the head AWAY from the direction of travel, momentum and casual contact tends to keep the cotter key's tails crimped, but...if the crimps fail that same movement easily forces the cotter key out of the half-link's pin, allowing the half-link to come apart.

Things get even more hazy when installing connector links that use cotter keys rather than a one-piece clip to hold the connector in place. At least once chain manufacturer says the proper method when assembling a master link that uses two cotter keys is to point one cotter key with its head in the direction of chain travel, and the other cotter key with its head AWAY from the direction of travel. Their logic is that no matter what happens, ONE of the cotter keys will be installed correctly and keep the master link together.

Personally, when installing a cotter key in any chain link, I put the head of the cotter key toward the direction of chain travel, then bend the tails of the cotter key tightly around the link's pin. My theory is that tightly bending the cotter keys' tails reduces the chance they will catch on something and break or straighten out. And if they DO break or straighten out, momentum of the traveling chain will tend to keep the damaged cotter key in place. That's my opinion and I'm sticking to it until somebody convinces me otherwise.

Isn't it odd, you can do $10,000 worth of repairs to a machine, tear it down to its base components and then rebuild it...and when you lay in bed at night you ponder if you put the cotter keys in the chain links correctly?