Hi Ned,

Thanks allot for your reply & the drawing.

I agree with you that I should forget about the standard profiles, it's
just that my software won't let me change the standard profiles to my
liking (or at all, other than for the Symmetry / Asymmetry factor of
the curve, i.e., make the follower start faster and stop slower, or
start slower and stop faster after leaving the dwells). However, I can
create a profile like the one you showed in AutoCAD.

Ned Simmons:
Isn't the curve with the largest minimum convex radius a
constant radius?

Yes I think so, and probably the smallest pressure angle as well.
Perhaps a "modified constant velocity curve" where you take a constant
velocity curve and then smooth the ends where it meets the dwells, with
a radius, (Just like the drawing in your previous message, but with a
..188" radius at each end of the curve) is the best that can be done to
reduce stresses in my case, I am not sure.

I checked with my spreadsheet program and using a constant velocity
curve for the inner cam profile gives a maximum contact stress of
around 145,000 PSI which seems great, but I did not check where the
curve blends with the low dwell. This will depend on what size radius
is used there i.e., at least .188 but I would probably try to go a
little bigger.

The guys at www.camcoindex.com told me you should always make the
minimum radius of curvature of the pitch curve (path of the roller
center) at least equal to the roller radius plus .0625". It only needs
to be equal to the roller radius to theoretically avoid undercutting,
but Camco says to add at least .0625" to this, minimum. I think this is
most important with a convex radius. I was able to get close to Camco's
recommendation with a Parabolic curve, but not quite there. Perhaps I
could use a modified constant velocity curve, shoot for .25" end
radii, and see what that does.

Ned Simons:
But maximizing the radius will probably not result in the lowest stress,
since it appears the force on the follower varies quite quickly with
displacement. Is that correct?

John2005:
Yes, the roller force varies according to the spring rates listed on
the drawings. The inner an outer rollers have equal forces at the
neutral position, but different forces at the cam low and high point
dwells. If I can just get the stresses to a reasonable or acceptable
level for the inner curve, I will be happy. I would like to just make
the cam and roller out of either hardened tool steel or 4140, instead
of something more specialized or exotic.

Ned Simons:
Making the radius of the convex part of the rise smaller lowers the contact stress.

John2005:
I am a little confused at this part. Don't I want to make the minimum
convex radius as large as possible to make the contact stress lower ?
Referring to your drawing, where the .379" radius blends in with the
..188 radius is a concave sharp point (if this were the inner curve it
would be a convex sharp point). It seems I need to find the optimum
size of the .188" radius to get the best contact stress. I'm thinking
in terms of the inner curve since that is the one with the highest
contact stress.

I'm not sure if I would want a 0.188" (or larger) radius at each end of
the curve, i.e., at both the low and high dwells. I may want to do this
just to keep a decent responsiveness between the cam and follower when
leaving the dwells. That is, I want the follower to start moving a
reasonable amount withing a reasonable time after leaving the dwells
and it may also be desirable if the follower was halfway to it's
maximum angular displacement when the cam is halfway at it's maximum
angular displacement. I might be able to do it either way though.

I just wonder if there is something that would produce lower contact
stress than a modified constant velocity curve having adequate size
radii blended at the curve ends.

Thanks again Ned, I really appreciate your help.

John