Spotface in Technical Drawings

Spotface is nearly similar to counterbores but there are some differences between them. Spotfaces specify clean and flat surfaces for the washers or bolts on the part. 

The differences between Spotface and Counterbore:

  • The counterbores are mainly used for hiding bolts or nuts.
  • The spotfaces are used to specify flat surfaces under the washers or bolts.
  • The spotface is used to make flat surfaces perpendicular to the bolt mounting direction.
  • The Counterbore diameter specifies the outer diameter of the feature.
  • The Spotface diameter specifies the flat smooth surface that contacts the washer, nut, or bolt-head.

In some conditions, the spotface depth is not specified on the technical drawing. the spotface depth changes according to the geometry of the feature on the product. The figure below shows the principles of minimum spotface depth. The depth of the spotface is the minimum depth value that needs to create a clean flat surface after milling.

Important Note: If there is a radius on the spotface dimension as shown in the figure, You should be careful. The spotface dimension only specifies the flat surface diameter. (not the feature outer diameter.) Look at the figure below.

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