Material Thickness around Keyway in Hub

[AB1733]

Hi All,

I'm trying to design a hub made of mild steel that will accept up to a 1-3/4" in shaft with a 1/2" Key.
I can't seem to find a standard for the material thickness (corner of key to O.D. of hub for example) around the key and it's been awhile since I've done this type of calculation to figure it out. I figured there must be some type of general rule out there that I haven't come across yet.

Thanks for your help.

 

[chicopee]

There is a lot of info. on the web about keyways in shafts.
To analyze stresses in keyways and keys, read MF Spotts "Design of Machine Elements"

 

[desertfox]

Hi AB1733

I haven't seen anything that relates the hub wall thickness to keyway size, however when designing the keyway and key the stresses you calculate are based on the shear and bearing stress for the given dimensions and normally the key size is based on the shaft diameter as a starting point.

look at these sites:-

http://www.roymech.co.uk/Useful_Tables/Keyways/keyways_index.html

http://www.engineering.union.edu/~tchakoa/mer419/MER419_keys-and_couplings.pdf

desertfox

 

[Tmoose]

How much torque are you transmitting?

For me a starting (and maybe a finishing) point is how big a bore FALK would punch in one of their nice steel gear couplng hubs.

http://www.delzer.com/rexnord/451110.pdf

The smallest size is a 1010G. They'd bore the hub for a 1.875 inch shaft. Not that far from 1-3/4 inch in my book. Looks like the hub is 2.7 inch diameter. page 16.
Note their standard fit is a slight interference. Setscrews and keys can't be counted on to resist micromotions, fretting and wear by themselves if there's an appreciable side load or uneven torque.

 

[unclesyd]

You will find a very through discussion for the design of keyways starting on about page 350 tine excerpt from Mcgraw-Hill.

https://highered.mcgraw-hill.com/sites/dl/free/0073121932/365766/chapter07.pdf

 

[Cockroach]

You're mostly concerned with shear across the lateral plane bearing the face load. Obviously the torque capacity is a linear function to key length, once you have the bearing load from torque analyzed, you naturally progress into the lateral plane and look at shear as a function of key width. So it would be the width and length of the key driving the computation, not the height and length of the key as in the load bearing face calculation leading to torque.

You've had some highly qualified experienced responses (DesertFox, Uncle Syd, et al) point you in the right direction and website links. All I would add to this is probably FEA and base the output to your hand computations to validate the model.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[Tmoose]

The (shear) stresses in the key are important, but the material beyond the keyseat in the hub (hub OD) present a limit, too.
FALK has different maximum bore limits based on key profile. If I need to bore a particular hub for a larger shaft, using a low profile key can help me do it.