Hi folks.
I've got a project that requires a cam lobe of specified duration running in a yoke/fork with minimal clearance through complete revolutions.
 Say the yoke/fork had a 2" opening. A 2" diameter cam follower offset .1" from its shaft centerline would oscillate the yoke .2 per revolution.
But ......
I want an egg shaped cam lobe that will have a duration of lift as much as possible per revolution but always measure 2" diameter at any point as to keep the yoke/fork free of backlash. I assume it would be shaped sort of like a guitar pick. 
Is there a formula, or generator for this sort of thing ?
I can make a crude sketch if necessary.
Thanks.

In the attached, can I assume that as long as the red and blue are exact mirror images of one another that the OD would be the same anywhere around the periphery ?

uh .... nope. I see that wont work ...... standing by 

Arts Gearotic might help?

http://gearotic.com/

That did cross my mind. I have it on a different pc, will check it out, thanks.

Didn't see anything related in the SW, might ask on their forum.
Here is an example of a triangular cam and yoke I found.
The radius's of the cam are ever changing but the ramp up and down at the duration segment are relatively gradual, not a pure motionless dwell but blended closely enough for practical purposes.
This is giving me a worse headache than the Wankel engine   
Cheers 

Found a link to exactly what I need, just need to figure how to draw it so I can cut it out with my nc mill.
https://www.youtube.com/watch?v=bSVPOGibdHA
I can get it pretty close with cad but wondering if there is a "dead nuts" way/formula/generator out there.
Thanks,
Russ

Thank you Brett, Graham and especially Mr. Reuleaux 
All is good now.
 

Graham knows all them fancy words! Reuleaux, who would have thunk?