Hitchcocks Forum

Help with a bit of info please from our technical types. I’ve noticed that some woodruff keys have a radiused form and others have what is described as a ‘flat bottom’. Why this difference in design? Thanks.

Presto a woodruff key looks like this:-

http://www.hexagon.de/gif/wn11_8e.gif

I am not sure what you are describing.

Thanks - I know what a woodruff key looks like - and what I'm describing is this difference: http://www.me.metu.edu.tr/courses/me114 ... odruff.gif

The truncated version A, may be for ease of assembly in a confined space.

I'm sure it doesn't matter which form is used as there won't be any stress down at the root of the slot. Indeed, if the shaft is on a taper, there should be no stress on the key at all. The taper should hold without the key and it's only there for alignment and insurance. The advantage of a woodruff key over a straight keyway is that you don't need to machine near shaft shoulders which could cause weak spots. The snag with them is that you need dedicated cutters for the slots.

I accept that it doesn't much matter which is used - but as someone goes to the trouble to make both types I guess there is some distinct purpose behind the 'flat bottom' type. My own 'research' has produced no results at all.

I reckon it because of the different ways the slot is cut for different applications....


If the slot in the shaft is milled in by the cutter by moving it at 90 degrees onto the shaft the slot will have a round bottom therefore a round key is the best fit (NB some have the two ends flatted off the key to shorten its length).....


Some shafts however, have a their slot cut out by milling in from the end and moving along the shaft.....the same type of cutter is used for this to. This results in a long straight slot but the inner leading edge still has the normal circular radius. This type of slot is used for fitting pulleys and the like and it allow some positioning of the pulley along the length of the shaft and is tightened to it with a grub screw....The Woodruff key used for this application must then have a flat bottom to allow it to sit in the flat bottomed slot....hope this explains things.....Les

Just to be pedantic for a moment, a Woodruff key is the half moon shaped key found on most motorcycle applications as it is very easy to cut the recess for, another common type is correctly known as a parallel key which is not quite as easy to cut but is generally stronger than a Woodruff key, there are of course other types of key, tapered, Yale, five lever etcetra, end of pedant mode.

A Woodruff key slot is easy to cut the recess for? We will have to agree to disagree about that given the accuracy needed.

Papasmurf, we don't disagree, read again I said they are easy to cut,