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Alan,Originally Posted by olderdan
Machining/grinding cams can be the easy bit depending on the level of accuracy needed. Nowadays, OEM car and bike manufacturers make cams to quite incredible accuracy to ensure smooth and quiet running. Top end performance applications also demand very high standards for life and performance. In the performance field multi-lobe cams often have the cam profiles angularly offset to account for twist in the shaft. Some also have slightly different profiles for each cylinder to optimise for differences in temperature, and mixture strength between cylinders.
The old hotrodders' trick of grinding the base circle to get more lift just does not cut it these days at the top end, although it is still practised by some old school cam grinders.
As you say designing the profile is the tricky bit, both for performance reasons and mechanical reasons. You can design a cam to get air into the cylinder but mechanically the profile might induce valve train destroying vibrations due to excessive acceleration and jerk. Even if those parameters are in the acceptable range there may be harmonic vibrations in the rest of the valve train. That is less of a problem with non-pushrod engines. The design of cams for low speed and/or model engines is generally less critical and people get away with what might be regarded as poor design, such as joining a base and top circle with a simple curve as per your illustration. Having said that, probably millions of cams have been built that way and worked well enough in non-critical applications.
I have developed some cam design and analysis software which will calculate the optimal mechanical profile from required performance parameters. Even then I do a dynamic analysis of the whole valve train before being happy with it. There are some very Q&D videos here
https://www.youtube.com/playlist?lis...SvlfD6C_oAHYK3
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