This is a continuation of the previous entry. Go back and read it first. There is a lot of talk about what design method is best to design a cam profile. You hear words like polynomials, splines, B-splines, NURBS, and circular arcs. I approach most things in a realistic way. Everything that man creates goes through a design phase, usually right after the idea is created. Sometimes the design looks good in the design world, but will not work in the real world. This can certainly apply to cam design.
When a modern cam profile is designed, the lift table is actually what is designed. The shape of the lobe is a product of the lift table and the tappet used. The lift table is simply the movement of the tappet compared to the rotation of the lobe. Usually displayed in 1-degree increments, the lift table will show the tappet lift per degree of rotation. A good display will show the lift out to seven or eight decimal places. Except for the precise numbers, really simple... right?, nothing complicated.
If your mind is capable, a lift table can be designed just from your brain. There are people that can actually do this. For real. No computer, no calculator involved. What do you call this cam design method? A cam profile designed this way is unique, because any numbers can be used, which could create a profile that no other method would be able to do.
In the beginning, the shape of the lobe was designed as the first step. No thought was given to a lift table. There was a base circle diameter and the maximum lobe lift with a nose radius. Two lines were drawn tangent to connect the base circle with the nose radius and tada; you have a cam profile. In this case, the profile shape would create the lift table. Make sense so far. When people started to analyze the movement of the tappet from the profile shape, the lift table was created. It was far from acceptable compared to today's cam profile designs. People in the know soon realized that by controlling the tappet movement, more power was made by the engine. We are just talking about tappet movement, nothing about opening and closing, centerlines or lobe separations. That is camshaft design, which comes after cam profile design.
Through the years many techniques, formulas, programs, and methods have been used to design cam profiles. Some will create a smoother profile than others. Some are easier to use than others. When a cam profile is created, it has specifications that the designer is trying to meet. Important to most people are the lift and durations of the profile. If the profile was "maxed-out" (my terminology) when designed, the velocity, acceleration, and jerk curves are all at maximum levels, but will still produce a smooth, reliable profile. The duration figures at different tappet heights will also be at maximum values. In order to get more duration (more area), the other maximum levels will have to be exceeded.
Whatever method is used to design a cam profile, the real world will cause each method to reach the same limitations. Many designers will focus on the smoothness of the profile and pick a particular method because it does indeed smooth-out the profile. It looks good on paper or the computer screen, but more area under the lift curve is not increased. This area is what makes power. That is the reason for the larger base circle diameters and lifter diameters. They will allow more area to be created without increasing the other important limits. Software alone will not create more area without exceeding the limits. If the area did not matter, we could have just kept creating a shape and not worried about how fast to raise and lower the tappet.
Like most things, time will tell. I am always following and studying this subject. The method of manipulating the numbers in the lift table looks good to me. A program would need to be created that would do this and then display the velocity, acceleration, and jerk curves. Maybe allow the user to input limits and ranges. That would be cool.