GD&T Most Important Symbol Explained

In this video I discussed the most important symbol in ASME Y14.5. This is the MMC symbol that has three meanings depending on where it’s used as I discuss in the video.

1. As a concept maximum material condition is a convenient way to distinguish between the maximum size and the minimum size of the gap between mating parts. If we compare the maximum size of external feature and the minimum size of an internal feature, we will know the minimum room, and the maximum room between those two parts at assembly.

2. The next use of MMC is in the feature control frame with the tolerance value. In this case it means that the tolerance applies only at the MMC size of the feature or features being controlled by the feature control frame. At any other size, additional or bonus tolerance will be available.

3. The next use of the MMC symbol is in the feature control frame with the datum references. If the datum feature is a feature of size, then a material condition applies. The default material condition is regardless of material boundary (RMB). If we add the MMC symbol we are creating a maximum material boundary (MMB) which allows fixed gaging when setting up to inspect a part with feature of size datum features as I discussed in the video.

#engineering #drafting #gdt #cmm #metrology #symbols