keyway and key design 1

[Jamaz17]

Hey, I'm new to this foruma and I have a question about key design. I have a rotating shaft and hub transmitting 2000ft-lb of torque. How do I calculate what size key I need in order to have the key not shear?
It's been a while since I have done any of this kind of design, any help is appreciated.

Thanks in advance,
-James

 

[israelkk]

Machinery's Handbook

 

[arto]

Also, look in peterson's Stress Concentration Factors book for Shaft SCF's

 

[Jamaz17]

Thanks for the info, I'm looking in the Machinery's Handbook now and I see a lot of info on keyway sizes, but nothing on "shearing" keys? I have the 25th edition. Am I looking in the wrong spot.

thanks again,
James

 

[swertel]

Simple shear stress formulas.

Torque on shaft divided by radius of shaft gives tangential (shear) force divided by the area of your key. Change the length of the key as appropriate to get your F.S. The width remains per the standard as defined in the Machinery's Handbook.

--Scott

For some pleasure reading, try FAQ731-376

 

[Jamaz17]

Thank you very much A big help

-James

 

[Metalguy]

Jamaz17,

You need to keep in mind that the key will be loaded transversly, and its strength will be lower than the usual long. test properties. It can be MUCH weaker if the steel isn't "clean".

 

[Jamaz17]

Ok thanks for the tip metal guy. One other question just for my personal interest. Is 2000 ft-lbs a lot of torque for a key to transmit on a 1 1/4" shaft? (Using a 5/16" square key as suggested in the machery's handbook.) Is there a certain grade of steel I should be using to manufacture the key, hub and shaft ?

Thanks again for any advice.
learning lots today

-James

 

[unclesyd]

Come back with a little more information on the hub size, type and rpm of shaft and hub, it will be great help in recommending a material.

Will there be a lot of starts and stops?

You mentioned "shearing keys" did you want this key to shear as a safety feature?

There are quite a few materials available off the shelf but would meed a little more information for a firm recommendation.

 

[Jamaz17]

Here's some more info 2000 ft-lb torque @1000rpm.
I don't want the key to shear as a safety factory at the moment because I am just doing this for testing. There will be a lot of starts and stops though. I am restricted to about 2 - 2 1/4 in dia on the hub size, length is not an issue.

also does anyone have a good web site for material information? Such as modulus of elasticity, modulus in shear, etc.. I looked in the Machinery's handbook but I'm not sure what number I should be using.

Thanks again

 

[CoryPad]

[blue]Jamaz17[/blue],

http://www.matweb.com

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[GregLocock]

My gut feel is that 2000 lb ft is a lot on a 1 1/4" shaft.

3000 Nm, r=.015, F= 200 000N, so you must have at least 150 mm of keyway at the yield strength of mild steel, that is quite ridiculous.



Cheers

Greg Locock

 

[howard1954]

2000 lb-ft on a 1-1/4 diameter inch keyed shaft is not feasible. If you are restricted to a 2-1/4 hub diameter, you should consider using a splined connection (sort of like many keyways).
For reference, the standard SAE F spline 8/16 DP 15Tooth and 1 inch length, it has a major diameter of 2 inch and a torque capacity of 24,245 lb-in at 25,000 psi shaft stress. (see SAE J744). Using higher strength materials and longer lengths can lead to smaller diameter splines, such as SAE C-C spline 17 tooth 12/24 DP, 1-1/2 MAJOR DIAMETER and 0.7 inch length rated at 10,777 lb-in at 25,000 psi shaft stress. Using a 1.56 inch long spline will give you the required 2000 lb-ft. This will still leave .38 inch material wall section per side in the hub.

For more information on keyed shafts see Standard Handbook of Machine Design, (Shigley, Mischke), McGraw-Hill, (Chapter on Couplings).

Howard Schwerdlin