# To find mode of key failure

by stardinesh
Tags: failure, mode
 P: 4 i hav to find out why the key in output pulley fails due to sudden forward and reversing(in gearbox of lathe)i did some theoretical calculations in crushing & shear stress.please tel some solution regarding analysis of the key
 P: 477 Hi there, You question or comment is not terribly clear to me. Would you be kind enough to post a picture or drawing of your problem, and what exactly you are looking for. Cheers
P: 735
 Quote by stardinesh i hav to find out why the key in output pulley fails due to sudden forward and reversing(in gearbox of lathe)
it fails because of inertia. A sudden change of direction of motion means a lot of acceleration & a lot of inertial force(Iα/r) & probably a lot of impact load.

What kind of failure did you observe/calculate for the key?

 P: 4 To find mode of key failure sorry,i cant upload the figure, imagine a key resting on the key way of shaft,then due to sudden forward & reversig the key makes the keyway(of shaft) larger,thus decreasing the area of contact of key to the shaft along the rectangular perimeter, i need a analysis software to find at what place the key hits the keyway harder.i.e,to do force anlysis in the key
P: 735
 Quote by stardinesh sorry,i cant upload the figure, imagine a key resting on the key way of shaft,then due to sudden forward & reversig the key makes the keyway(of shaft) larger,thus decreasing the area of contact of key to the shaft along the rectangular perimeter, i need a analysis software to find at what place the key hits the keyway harder.i.e,to do force anlysis in the key
I hope that you do know that an analysis software is not a magic wand. It is only an engineering tool, not an engineer itself.
Before jumping to a shiny graphic solution, you should understand the physics of the problem. I am still not sure what you mean by making the keyway larger. In practice, key is designed to deform first, to prevent any damage to the shaft(you should know which one is costly?? shaft or key!!)
In the mean time, try going through this
http://www.motioncontrol.com/product...o-Gear-Reducer
 P: 4 thanks for the address provided,in that 2.keyed shaft diagram,the effective key height reduces (h)as i told earlier the key hits the keyway of shaft ,thereby increasing the width at the edges(the contact area of key to shaft reduces),thus decreasing the torque transmitted by the key. i know the failuring area, and conducted practical tests to find the minimum speed (recorded by a tachometer) when suddenly reversed by the shaft. now i cant know how to minimize the enlarging of the keyway at the edges,i wil try to go through fully the material u provided.
P: 735
 now i cant know how to minimize the enlarging of the keyway at the edges
keyway doesn't get larger, the key deforms & finally fails

 In practice, key is designed to deform first, to prevent any damage to the shaft(you should know which one is costly?? shaft or key!!)
 P: 4 what u r telling is correct from design point of view,but my sir told this problem to solve it.i wil go and ask him what exactly did he see, thanks

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