DIYbanter - View Single Post - Request for help finding a cam curve that will have lower maximum contact stress than a Parabolic curve (and link to CAD and JPEG files)

In article . com,
says...

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.

I mentioned 52100 bearing steel in an earlier post and still think it's
worth considering.

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 ?

Sorry about that, too many concaves and convexes for me to keep
straight.g What I meant is the stress will be lowest when the follower
nestles in a concavity in the cam with the cam and follower radius
equal. As you said earlier, you do want to leave a little clearance, but
I wouldn't be afraid to go a little tighter than Camco's recommendation.
I'd imagine 1/2" diameter followers are more typical of their smaller
indexers, so an allowance of 1/4 the roller diameter seems consistent
with their advice and reasonable to me.

Referring to your drawing, where the .379" radius blends in with the
.188 radius is a concave sharp point

No, the two radii are tangent so there's no bump or point. In my layout
the small radius is .094 (3/32).

(if this were the inner curve it
would be a convex sharp point).

On the inside cam the small R would be tangent to the high dwell rather
than the low dwell as shown for the outer cam - again no bumps. The cams
aren't required to be true conjugates are they?

Ned Simmons