It’s been many years since ASME Y14.5M-1994 introduced the controlled radius symbol. Yet, we will still frequent find individuals in the industry who have never seen the symbol, nor know what it is. The symbol is CR. Really, a controlled radius is actually just a radius that is a fair curve, with no reversals. I’ve not read ASME Y14.5-1982 in a very long time, but I believe this is actually similar to the original definition of a plain ol’ radius from the older standard.
Since ASME Y14.5M-1994, a simple radius has no fair or reversal limitation. As long as the arc of the radius feature’s profile falls within the tolerance zone, it is considered acceptable. These are represented by R.
So much time has gone by since the introduction of CR, I am left wondering why so many people have never seen it. The reason CR was created, as it seems, was to allow engineers to specify a radius without the need for it to be fair or non-reversed. This is good for breaking edges or filling corners. A CR would be more useful when fit and/or function is important, such as guiding features. In this way, the added expense of a creating a fair and non-reversed curve would only be employed when it is necessary for function.
