The depth symbol is used to indicate a measurement from the bottom of a feature to the outer surface of a part. The depth symbol is commonly used for holes, but can be used on other features as well, such as slots or counterbores.
Let’s look at an example. The part in Figure 1, below, has two sets of blind holes which are dimensioned with depths of 1.5 and 1. Looking at the cross section of this part, we see that there are angles at the bottom of the holes, indicating that the holes have been drilled. For our depth measurement, the bottom of the hole is considered to be the deepest location where full diameter is achieved. Therefore, we do not measure to the bottom of the cone for our depth measurement. The dashed lines shown on the cross-section of the part indicate where the depth measurement is taken.
Figure 1: Depth of Feature Indicated by the Depth Symbol
If the depth dimension isn’t clear because of a curved or complex surface, the part should be dimensioned pictorially, without the depth symbol. The part in Figure 2 is a good example of this. Because of the curved surface, the depth measurement would be unclear without a section view indicating where the depth is to be measured from.
Figure 2: Part with a Curved Surface
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