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David Billington

wrote:
On Sat, 20 Jun 2009 20:57:14 -0400, "John"
wrote:

"Wes" wrote in message
...

Mark Rand wrote:

Woodruff keys were not designed for transmitting torque and should not be
used
for such. It causes the keyseats to self destruct.

I'm curious about your comment, I've seen woodruff keys in many things.
The most notible
thing is the handles on a bridgeport. That may be a case of location
being primary over
torque since those are not stressed.

I'm tempted to just cut it for a pocketed square key and be done with it.

I *thought* there might be some sort of rational to the woodruff key that
made it better
than a square key.

Wes

A square key usually is held by a setscrew. I cant think of a time that a
woodruff key had a setscrew on the shaft.
A woodruff key cant work out of the slot. they are used when the part has to
slide along the shaft.

John

They are also used on tapered shafts. Look at the flywheel on your
average single cyl air cooled engine. (where they also transmit torque
- starting torque as well as, in many cases, accessory drive torque.

Just blew two so-called "facts" about woodruff keys with one example.
Not a sliding fit, and delivers torque.

Actually in that situation the taper handles the torque and the woodruff
does alignment. The woodruff key or some method of alignment is required
to position the flywheel and the magnets for the ignition, the friction
fit on the taper handles the torque unless severely overloaded. I've
never seen an aluminium woodruff key but wouldn't deny their existance
if required for an application. I've dismantled a few small engines in
the past and have never seen other than a steel woodruff key used.
Then go to the harmonic ballancer (front pulley) on many car engines -
Woodruff key there too - definitely not a sliding application, and
definitely delivers torque - runs the alternator, air conditioning,
and power steering loads.

Maybe the previous poster got sliding wrong, the part located by the
woodruff is slid into position, but is not necessarily a sliding part.
The main load transfer for items like crank pulleys is via friction due
to the clamping load and not via shear loads on a locating key.

It is also used to hold the drive pulley on many
alternators/generators/etc as well as keying timing gears to both
camshafts and crankshafts..

I wouldn't argue against that but the loads are somewhat lower
A woodruff key is used where the loss of the key through lateral
movement is to be avoided. It is also used where a controlled torque
shear is required. They fail very predictably under high impact shear
loads, providing a certain level of mechanical protection to
drivelines.