CNC TRUECUT / MACHINING REFERENCE
Socket heads and countersunk screws: machining reference
Match clearance, counterbore and countersink preparation to the selected fastener, with tools for 82° and 90° conical geometry.
Use the specified fastener dimensions
A socket-head cap screw may need a clearance hole and a counterbore for its head. Head diameter, head height, socket size, bearing surface and required clearance are separate dimensions. Obtain the selected fastener’s drawing or the specified standard before choosing a counterbore tool. This reference does not assume one catalogue’s dimensions fit every screw.
82° and 90° countersinks
The angle in a countersunk screw callout is the included angle. Match it to the tool and hole preparation. An 82° cone and a 90° cone produce different depths for the same diameters. The countersink calculator accepts either angle and uses the entered pilot and finished top diameter.
Do not confuse top diameter with tool travel
For a countersink, the ideal conical depth is measured from the plane of the pilot diameter. A tool’s flat tip, spot or prior chamfer changes the actual contact point. Measure a test feature and adjust the setup from the drawing’s required finished condition, instead of treating the theoretical cone as an unqualified machine offset.
A useful setup order
Identify the screw and standard, select clearance, check wall thickness, establish head or cone dimensions, and define inspection. For multiple holes, use the bolt circle or linear hole pattern tool to compute nominal centres. Those coordinates do not apply drill compensation or produce a complete CNC program.