Load capacity on a set screw 1

[EngApp]

A cone set screw (any hardness/material/or size) is in the vertical position and a load is applied perpendicular to the screw (only making contact with the taper of the cone).
What type of formula could I use to calculate how much load the set screw can bear.

 

[GregLocock]

Well, practically speaking, zero, reliably.

However for the first cycle

1)of the order of the area of the engaged tip times the shear stress of the rod.

2)The axial load exerted by the set screw *.15

3) as 1 but with the side view triangular area, not the circular area


Cheers

Greg Locock

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

 

[EngApp]

Thanks, to go into more detail, there consists of an insert positioned at the same degree angle as the taper (45 degree) and encloses the taper on one side. So, as the screw is driven downwards the insert extends outwards. The load is applied to that insert which only makes contact to the tapered surface of the screw. Calculating the surface area of the taper is no problem but as to know an estimate of what the screw can handle is of big help because i can just multiply the number of screws used if not enough.

 

[jte]

I don't deal often with set screws - well, virtually never... But consider taking a look at

http://www.unbrako.com/

and downloading their "engineering guide".

jt

 

[Tmoose]

Some testing I did long ago suggested something like 1000 lbs to force a cup point set screw (as used in pairs to "lock" a pillow block bearing) axially along a mild steel shaft. Similar numbers appear in sources like the preciously mentioned Unbrako guide. I believe Part of the holding power of a setscrew in a simple hub, and all the stability comes from the semi-cylindrical seat opposing the setscrew's push. The few hubs I've seen with multiple opposing screws fail quickly in operation. Really only reliable holding on lampshades.

But, like others have said, a single setscrew does not make a great load bearing locating device. Any cyclic load will make things wiggle, and after a few thousand wiggles the joint will most likely be loose.