Lift Table

The first thing that comes to mind when one thinks about a cam profile is the actual shape of the lobe. In the cam profile design world, the lift table is the cam profile, not the shape of it. The actual cam profile shape (excluding the physical dimensions) is of little importance.

As talked about in previous blogs, the lift table shows the tappet height at each degree of cam profile rotation. There is also a sample lift table shown in a previous blog. What may not be clear to some is that the lift table does not represent any particular type of tappet. The table only shows tappet height. The lift table could be exactly the same whether the tappet was a roller or a flat style. The table could also be the same no matter the diameter of the tappet or roller wheel. Sound confusing? It’s really not.

The cam profile shape is created by the lift table and the tappet used. As long as it is physically possible, any tappet can be used with any lift table. Using the same lift table, the type of tappet will determine the shape of the cam profile. Obviously, a roller profile and a flat profile will look different, but the valve movement will be exactly the same. The tappet height at each degree of rotation will be the same. The lobe shape combined with a particular tappet will determine the tappet height. Make sense now?

Many times a flat profile cannot be made from the same lift table as a roller profile, because the velocity will be too high for the diameter of the flat tappet face. A roller profile might encounter a severe negative radius when made from the lift table of a flat profile. Make sure you have read and understand all of the previous blogs if this is not making sense. If none of these or any other physical problems occurs, the same lift table can be used to produce a flat and a roller cam profile. The finished cam profile would still need to comply with all of the other design parameters to be a good profile.

To sum it up, the profile design procedure will create the lift table. Based on the type of tappet that will be used, the cam profile shape is then created and the final design is accepted after much trial and error until all of the parameters are met. Computer software allows all of this to happen very quickly even though separate steps are actually taking place.