Spotfaces – All About

spotface example on part

A spotface is a machined section of a part that allows a fastener to sit flat. This is usually a bolt head or washer but can be other fasteners. A spotface is generally very shallow and removes just enough material to create the clean, even, flat surface. Spotfaces are most often used when machining castings or forgings. Spotfacing is done using a manual or CNC milling machines.

Spotface vs counterbore

A spotface is functionally no different than a counterbore. A counterbore usually references a feature that is deeper than a spotface. While a spotface creates a flat mounting surface, a counterbore acts to recess the fastener. It would be safe to call a spotface a counterbore but not the other way around.

cutaway examples of countersink and counterbore

Spotface vs countersink

The primary difference between a countersink and a spotface is that the countersink has an angled bottom whereas a spotface has a flat bottom.

Spotface symbol

Spotface Blueprint GD&T Symbol SF in a u
Spotface symbol
Counterbore Blueprint GD&T Symbol u shape
Counterbore symbol

The symbol used to callout a spotface is the counterbore symbol with the letters SF in the middle. This is per the engineering drawing standard ASME Y14.5. At times, a blueprint may indicate a spotface feature simply through the use of a counterbore symbol. Additionally, older drawings and blueprints may reference a spotface as SF or SFACE instead of using the symbol.

How to dimension a spotface

spotface blueprint example

A spotface is dimensioned by specifying its diameter and depth. At times the amount of remaining material may be specified instead of the depth. The symbols for diameter and depth are shown below.

Diameter Blueprint GD&T Symbol o with line through it
Diameter symbol
Depth Blueprint GD&T Symbol line with arrow pointing down
Depth symbol

Spotface example

spotface cutaway example

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