Shaft Keyseat

Look at the key profile it has a chamfer and the radius has to be smaller than the chamfer but NOT TOO small since it is a stress concentrator and the shaft could break under load. The corners MUST have a radius MUST NOT be sharp!!!!!

The site linked here gives some data re: Woodruff keys, but please note the disclaimer at the top of the linked page.

You could also follow up some of the links on Wikipedia.

Rather interesting is that nick name has identified the proper principle, and JohnDG's Woodruff key link applies the concept. Even so, a few other online keyway dimension sheets do not mention fillets/chamfers at all, and the keyway cutters I have found so far are sharp at the corners. I have, albeit rarely, seen keys of circular cross-section.

The link suggested by JDG presents as well dimensions for other key types.

The Woodruff key is used for low torque transmissions with respect to shaft dimensions or for conical (tapered) shaft ends. It has an increased notch factor and reduces the smallest torque transmission section more than rectangular keys.

If the tools are without chamfer or radius it is because they can be used for other operations as well.

I did not propose a link because I consider that it is also needed to do some research to get the information but I consider also that the basics have to be communicated and explained since not everywhere (and what you say is the proof) are they clearly presented.

I consider that my answer has to put the interested person on the right track but not to make his work.

I found a section in the Machinery's Handbook that says in general practice, chamfered keys and filleted keyseats are not used. However, if you need to decrease stress concentration, they provide a table for suggested keyseat fillet radius and key chamfer.

In the case of a machine shop selling keystock, I feel we may need to have sharp corners because a customer is not expected to have chamfered keys.

Do that and accept to pay for the broken shafts! Take a VERY GOOD insurance.

I do not have it any more the sample but I had one of a 80 mm shaft broken under a not too high torsion ONLY due to the sharp corner in the key seat. The fracture which happened after a quite small number of cycles was as theory (in which we generally do not believe because all those high degrees are stupid as several times mentioned by many participants) predicts it to be.

The fact that you took this recommendation from the Machinery's Handbook -a book I do not know since I never used it but which is the basic book by many participants - obliges me to take a strong position since what is written is a real "danger" for the book's user.

I bring here a few documents which show 1- that many fatigue problems are due to the key seat and how much the stress is increased by a reduced filler radius. I hope that many will have a look at the pictures and do not forget them. Any way I shall never try to use or to envisage the use of a book with such a flaw.

As you see many failures are due to the key seat alone or in combination with a shaft step and in the 1st picture how much the stress goes up with even a smaller reduction of the radius. The part of the article I copied says a lot and shows how in our profession it is COMPULSORY to keep abreast what unfortunately many do not do.

I always have a not too good feeling when for any kind of problem the same source (book) is recommended, may be I am envious since in my career I was always obliged to consult many many books!

Your posts on this thread have served us all well nick name.

Milo

When looking at a large literature it seams that the same source is every where mentioned. You have to be careful since it appears that the values are valid ONLY for a peculiar type of keys.I hope you have now several sources which could help.

If the picture are still too small then send by the private channel your mail and I shall send you bigger formats.

I agree that it is almost always stupid to have a sharp corner in any region carrying a load. The Machinery's Handbook also has a section on metric keys where it does have max and min chamfers or radii, but inch keys do not. Maybe that's another problem with the US system?

Most of the time I perceive the Machinery's Handbook as reliable because it has been alive for decades and it sites much of the information from national standards (ANSI, ASME, SAE, ASABE). However, I have found that even so-called "national standards", have mistakes in them, even after being around for decades. I'm usually dumbfounded when I come across a mistake that has crossed countless eyes over the years, yet was not corrected.