It has recently occurred to me, that almost all cam design computer programs assume the user of the program is somewhat knowledgeable about the "shape" of cam profiles. I have now concluded that "nothing could be further from the truth"!

Most new users of these programs have never spent any time in the careful analysis of "as-designed" or "as-manufactured" cam profiles. Have they ever completed a simple first and second "differences" of one cam degree spacing of an existing popular cam profile? The first difference of lift is called VELOCITY and the second difference of lift is called ACCELERATION.

During the past forty years, I have developed an entirely new technique in designing cam profiles. This procedure is different, in that I design the entire positive acceleration area totally separate from the negative acceleration area. This technique allows the designer to establish the maximum positive acceleration peaks and the MAXIMUM VELOCITY. Maximum JERK values are set and the maximum rate of change of jerk is carefully controlled.

What is the rate of change of jerk called? I call this "SNAP". And of course, the rate of change of snap must be "CRACKLE". This leads to what is the rate of change of crackle? It must be "POP".

Let us first discuss the SNAP of a simple constant velocity ramp. The rise of acceleration from the end of basecircle thru the ramp acceleration pulse and then back down to zero acceleration results in constant velocity. This rise in acceleration is the most common location for serious cam profile manufacturing problems to occur. I have developed a simple test for this problem. If the JERK difference at this transition point exceeds .00001000 inches per degree cubed (in one half of one degree of cam rotation), then this area of the design should be redesigned if the camshaft manufacturer wants to make the profiles ACCURATELY!

If ZERO ACCELERATION is used to DWELL the MAXIMUM VELOCITY, this same test should also be met.

It is my experience that an entirely different program should be used to design the NEGATIVE acceleration area. The designer can then spend more time in optimizing the RADIUS OF CURVATURE across the nose of the design. If a cam design program uses the SAME POLYNOMIAL exponents to shape both positive and negative areas of the cam, then the positive acceleration area is ALWAYS COMPROMISED in order to fix the nose radius problems.

In the case of roller follower tappets this is especially true, as the design should not have a large reverse curvature in the flank area, if the cam must be made with a normal FULL SIZE DIAMETER grinding wheel.

As for a normal flat face, or nomimal 35 to 70 inches of spherical radius tappet design, the designer is always concerned with too much velocity for a given tappet wear surface diameter. So why not fix this maximum velocity with a separate positive acceleration program before designing the negative acceleration portion of the cam profile.