Tolerance Those Slots Right
The Y14.5 Standard gives us two ways to tolerance slots. The one specifically shown for slots is on the first drawing. It requires two position tolerances ( both labeled BOUNDARY) and leaves the allowable variation of the rounded ends a little fuzzy. The second method shown on the lower drawing is a little cleaner and actually does a better job of defining the slots.
On the lower drawing the size and form of the slots is controlled by the profile of a surface tolerance. The location and orientation of the slots is controlled by the position tolerance. The application of the maximum material condition modifier means that the inner boundary of the slots may not be violated by the surface of the slots. Even though the control is on the boundary because of the MMC modifier, the word BOUNDARY is required by the 1994 Standard. The inner boundary of each of these slots is 9X17. However, the slot on the lower drawing is more clearly defined by the profile of a surface tolerance. Why not clearly define slots using the lower drawing’s approach? By the way, this approach will work for all internal and external shapes. On external shapes it is the outer boundary that may not be violated.
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