What type of keyway is this? 1

[MathewB_FKC]

Guys,

I'm having a hard time identifying the type of keyway featured on this shaft. The mating hub is machined "opposite" of the shaft to accept a tapered rectangular key. I need to supply a new key for the piece of equipment but do not have an old key that I can measure nor can I find a specification that matches this particular style. I checked through various editions of the Machinery's Handbook with no luck. I thought it might be a Kennedy double key or a Peter's double key but the dimensions do not follow the standard. I'm starting to think that it's a custom design that doesn't necessarily follow a spec. Any and all help is greatly appreciated!

 

[Nescius]

http://www.educationportals.net/2015/02/different-types-keys-and-cotters-with-images/

Some people call it a "tangent key"...apparently often used in pairs on really big shafting. Each key is strong in one direction. Some google searching might turn up some specs for "tangent keys". I hope that helps.

 

[MathewB_FKC]

It's definitely some sort of tangential key, but I need to know if there's a particular spec it might follow. For example, if it followed ASME B17.1 with a class 2 tolerance I would be able to provide a key drawing with appropriate dimensions and tolerances. Thank you for the input, though! I've done extensive research to no avail.

 

[Nescius]

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

Metric...and poor resolution...but maybe it's a start.

 

[Nescius]

More breadcrumbs...

DIN 268
DIN 271
ISO 3117
IS 2291 (Indian Standard I was able to find, claims equivalence to ISO 3117, see attached)

Probably all metric, though.

 

[Artisi]

Don't understand your problem, you have all the necessary data to draw / manufacture the key, the only info missing is the taper which you can physically measure.
It's more than 55 years since I last hand made and fitted a tapered key, however, think I could still measure and rough out a key before smoko and for the size involved probably have it fitted and finished first thing after lunch.


It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[MathewB_FKC]

Artisi,

I just want to verify the recommended tolerances and dimensions. I know that it will be a 1/100 taper but as far as width fit tolerances and height tolerances I'm still lost. I've got the key information for the coupling in the system so I can use that as a reference. What's throwing me off is that the key seat for the shaft and the hub aren't nominal imperial or metric dimensions which isn't typical of most keyways. I don't have the ability to measure the existing keys since the current system is still in operation. The keys will likely need some field fitting but I'd like to get the key manufactured as close fitting as possible. Field work will be very difficult to perform in this circumstance.

 

[Artisi]

If it's a tapered key, there won't be any clearance / tolerance, a key of that size would need to be hand fitted by an experienced competent trades person, so that means a snug fit sides, top and bottom. Well that's the old fashion way and certainly one I would undertake if I were asked to do it, but maybe I'm just old fashioned and from the old school, so today, maybe the way to do it is to machining a key and then belt it into the shaft / hub keyway with a big hammer

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[MathewB_FKC]

Here's what I have for the coupling key. The larger key will be very similar.

 

[Artisi]

Sorry missed the point about tolerance for manufacture, the dimensions you can, with a bit of calculation establish - as for tolerance it would be ++ something minus nothing - as for how much to add ???? maybe 0.010" to width and similar to height - that's assuming the shaft / hub keys haven't been "working" and the keyways are 100% - you will also need to consider the key width using the max tolerance on depth for hub and shaft, if the seat depths are at maximum 1.133" when the width and height will be at maximum size. Therefore you need to make the keys to suit the max. dimensions plus a fudge factor.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[CouplingGuru]

The beauty of tapered keys is the tolerance isn't all that critical. The taper is what is critical, you can verify that with bluing to insure you have a high percentage of contact.
Because it is a tangent key, the height is more critical that the width (which is mitigated by the taper). It is actually a real nice design, especially for large lower speed shafts.

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