Knurled bushing calculation

[lattedicocco]

Hi guys,
does anyone know which is the methodology calculation of knurled bushing?
In particular, I neeed to calculate the interference fit for transmitting a specified torque through a gear/shaft assembly: should I perform a FEM calculation of pressfit bushing and verify the ammissible torque?
Does it work a similar simulation?
Thank you

 

[TVP]

In English, we use "spline" instead of "knurl" when discussing torque transmission of shafts. Here are some links with information on the subject:

http://www.google.com/#sclient=psy-...34,d.aWc&fp=78ff6e574ada34ce&biw=1145&bih=797

 

[kingnero]

spline is different from knurling...
I doubt you'll be able to accurately calculate anything knurling related, as there is no given data available (what is the interference pressure, what is the contact surface/area/...).

I'd say to determine it empirically... and expect a large variation on your different samples.

 

[drawoh]

kingnero,

In addition, a spline is basically a gear, cut accurately and consistently. Is there a way to specify and cut a knurl that will work the same way every time?

--
JHG

 

[CoryPad]

drawoh,

Most knurls have engagement dimensions on the order of hole size and shaft variations (diameter, circularity, runout), which complicates things. Yes, it is possible, but likely there are better solutions.

 

[lattedicocco]

Kingnero,

I agree with you when you say that a spline is different from knurling.
The approach used in my experience is essentially empirical as you suggested, in the face of expensive prototypes: I would like apply a FEM calculation, if it's possible.
The problem that I see in this way is related to strong plastic deformations that occur when the steel bushing penetrates into an aluminum part due to interference.
Could an explicit analysis help to achieve convergence in the FEM calculation during the pressfit?

 

[drawoh]

CoryPad,

When I call up knurls on drawings, I am looking for a grippy surface. My diameters and locations are sloppy. Do knurling tools support anything better than this?

--
JHG

 

[chicopee]

I would opt for shrink fit bushings instead of knurled bushings.

 

[Cockroach]

The purpose of a knurl is to build up the OD of a piece intended to be an interference fit with another piece. As such, knurling is often used to fix a machining error in over turning a shaft. We're talking thousands of an inch over diameter in this case.

I have seen knurls being used in order to increase torque capacity between mating pieces. What you want is a heat shrink and not an applied axial load for make-up, obviously you would destroy the knurled surface and remove any hope of achieving a superior interference fit.

To my knowledge, I may be wrong, there is no standardized method in determining increased torque capacity between an knurled surface and smooth bore. I think it is done experimentally using a sacrificial specimen.

Good luck with it, very interesting problem.

Regards,
Cockroach