what's single/double keyed mean?

[Sofa]

in regards to hubs and cranks

[daino149]

Is that the same as keyways? If it is, Kris explained that in the Onza thread:

A keyway is one method of attaching a round bar inside a round hole so that it doesn’t rotate. Essentially, grooves are cut in the bar and in the hole, and a key is inserted that fits in both grooves, preventing the bar (ie axle) from turning. The bar (ie axle) is then tightly pressed into the hole (ie hub). Generally, if any play at all develops in a keyway, the strength is totally compromised, but I rode on a slightly loose Profile hub for months a couple of years ago, and it didn’t get increasingly worse.

Daniel

[ubersquish]

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

[john_childs]

Originally posted by ubersquish
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.

[Sofa]

thank ye kindly

[Gumbo]

Almost relevant fact alert!!1!!!

The keys are called Woodruff Keys in automotive use.

[andrew_carter]

So why not have 10 keyways then? Surely it wouldn’t take long/cost much/add weight to cut them.

I rode an Onza with what I now realise must have been a pretty loose keyway. You could definately feel significant play.

Andrew

[schroder]

Aha! A question I can answer

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

[andrew_carter]

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

[schroder]

Manufacturing

For those of us fiddling in our garages once you are set up to do one cut then two cuts seems trivial.

But in a manufacturing environment a lot of emphasis is put on how many parts a particular machine can produce in an hour. If it takes a minute to cut a groove then the machine can produce 60 single-grooved parts an hour, but two grooves would reduce that to 30 parts per hour, etc. The true cost of making that part would include the amortized cost of the machine, the operator, etc. etc. It doesn’t seem like much money, but manufacturing engineers will devote a lot of time and effort to reducing the cost of something by as little as ten cents.

As I said I don’t know what the tradeoffs are from 1 to 2 keyways but you probably don’t gain much going from 2 to 4 keyways, etc. Maybe the two keyways was a selling point (NOW, with TWO KEYWAYS!) I understand some bikes use a splined shaft which is the end result of what you are suggesting.

That is, if I know what I am talking about…