Cotter Pins And Woodruff Keys? What Size?

Question

i got a shaft that is 18.5mm in diameter that needs a woodruff key. i dont have the dimensions of the holes for the key. i was wondering if there is a rule of thumb to use a certain size key for a certain size shaft. any help is appreicated.

again i got the same question about the cotter pins. i have a hole with a diameter of 3.5mm in diameter. i would assume that you would use a cotter pin thats close to that size. maybe 3.2mm or 3.3mm?

Answer 1

See the following web site for recommended Woodruff key sizes for different size shafts.
The shafts are sized for torsional loads, and the keys are sized to resist that much torsion in shear.
Be sure to check that you are using a correct material for the key itself.

http://www.ecs.umass.edu/mie/labs/mda/dlib/mech_comp/keys/woodruff_key.html

As a rule cotter pin sizes are not critical since they do not carry any loads, but are only used to keep objects from sliding off a shaft. Usually any size cotter pin that will fit snugly in the hole provided will do the job. However I would shy away from aluminum pins, aluminum work hardens quickly after only a few flexes and if you have an aluminum pin you do not know how many times it has been removed and replaced.

Answer 2

woodfuff key is not a hole

it is a slot viewed from above
and a part of a circle from the side

If it needs a key then you know the size by looking at the keyway


and cotter pins are TAPERED, so one end passes easily thru' the hole and out the other side and a nut pulls the taper tight (the other end is too large to pass thru' the hole)

The point about the Woodruff key is that they are soft (not tempered) so that under a fault condition they shear

Answer 3

Go to a local hardware store and get them. You can go to the dealership and get a factory one for a few dollars. You need to know if it is half moon or square. Also if the key disintegrated there my be something wrong with the shaft as in seized or broken. If you go to the shop ask one of the mechanics they usually will help you out. Try using a dial indicator gauge to measure the slot in the shaft. Take a piece of paper, hold it over the shaft and rub slightly with a pencil, this will give you a very close image and you can measure the width from the marks on the paper.