what's single/double keyed mean?

in regards to hubs and cranks


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ubersquish wrote:
*so single-keyed would mean one key, and double-keyed would mean two
keys, presumably on opposite sides of the axle *

Yup.

Here's a page that shows a picture of a keyway.
http://www.robot-village.com/husky8.html
Check out pictures #13 and #14.
Picture #14 shows the long rectangular key.

Now just imagine that it's a Profile pedal spindle and a Profile hub
body and you've got the idea.

A google image search on "keyway" will find more pictures of keyways.


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thank ye kindly


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Finally, a question on this list that I can answer!

The reason you typically don't have more than one or two keyways is
simply the cost of cutting the keyways. The key transmits the torque to
the axle and if a key is not strong enough, the cheapest solution is to
just use a larger key (still only one keyway to machine).

Why two keyways, then? That's a good one, probably you can have a
smaller diameter axle overall (less weight) if you cut two small keyways
instead of one big one. There's always a tradeoff somewhere.

Definitely a loose key is a disaster waiting to happen, not only is it
going to fail *soon* but it is also probably damaging the keyway on both
pieces. Generally keys are made of a different hardness material to
prevent wear or "galling" of the keyway.

*Digression*
In some machinery a similar part called a "shear pin" is used between
two components for the specific purpose of cutting in two if too much
torque is applied. So if you want to really limit the size of the hill
you can attempt....

Phil


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But how can it cost so much more if you're already going to cut one?
Wouldn't it be worth it for more strength and less weight (as you said)?
Keep in mind that I obviously don't know what I'm talking about.

Andrew


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