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Composite tolerancing continues to confuse many folks. This series of 3 Tips will attempt to clear up the confusion. On the first drawing a position tolerance is applied to the 2 holes. This position tolerance locates the holes relative to the datum reference frame within 0.4 mm. That means the holes may misalign 0.4 mm with respect to each other.
Imagine there is a shaft that will assemble through the two holes. You would want the two holes to act as a single hole. There are two easy ways to specify this. One way is to add the continuous feature symbol to the size dimension. Symbol "A" means that the two holes should be considered as a single hole. For that reason, the 2X is omitted. The second method, symbol "B" is to replace the position tolerance with a composite position tolerance.
The upper segment is controlling the location of the holes relative to the datum reference frame. The second segment is controlling the position of the two holes relative to each other. Both approaches have the same meaning. This will keep the holes in-line as if they were one hole but they can be out of position which includes orientation by as much as 0.4 mm.
The remaining Tips in this series will show how to better control the orientation error. Watch the video of this Tip to see animations of these tolerance zones.