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...
Hi Ned,

Thanks for your reply. I will keep your suggestion about 52100 bearing
steel in mind. It makes sense since rolling element bearings experience
high contact stress. I have no experience working with it, and was
thinking tool steel might be easier to work with, but perhaps not that
much different. I also have some thin walls, so I need something that
deforms as little as possible during heat treatment.

The Metals Handbook groups 52100 with 4140 for machinability. It's use
in bearings requires stability in hardening, so I don't think that would
be a problem.

Ned Simmons:
The cams aren't required to be true conjugates are they?

If by true conjugate you are asking if the inner and outer curve needs
to be of the same type, I think it should. The way I have everything
set up, I can have a reasonable manufacturing tolerance on the rib
width, but I think it will work best if the inner and outer curves are
the same type. However, as long as the two rollers have the same
angular displacement about the swing arm pivot point, at any given
angular displacement the cam, it should be fine. That's the only reason
I say the curves should be the same type.

By conjugate I mean that the relationship between the followers is
constant. Conjugate cam/follower systems don't require springs to
preload the follower. Desmodromic valve trains are an example. If I
understand, you'd like the relationship between the followers to remain
approximately the same, not necessarily exact.

Ned Simmons:
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

I think the main difference between the curve you show and a constant
velocity or straight line curve is that the center of the arc radius
(the large .379" radius) for a constant velocity curve would be the
rotation axis of the cam. Then you put a radius on each end of the
straight line ramp. Would the curve you show produce a "near" constant
velocity. It almost looks like it would produce an eccentric type
motion somewhat like a harmonic curve.

When I get a few minutes I'll try another CAD (Inventor) layout of both
the inside and outside cams. I assume your acad .dwgs are to scale?

Ned Simmons