Calculate countersink diameter, depth, radial clearance and material removed for flat-head fasteners using hole diameter, head diameter and countersink angle.
The calculated countersink diameter is based on the fastener head diameter plus any optional oversize margin.
Calculate to see the countersink geometry.
What is a countersink? A countersink is a conical recess machined around a drilled hole so that a countersunk fastener can sit flush or below the surface.
How is countersink diameter selected? For a flush fastener, the countersink diameter is normally based on the actual fastener head diameter, with manufacturing allowance if required.
How is countersink depth calculated? For an ideal conical countersink, depth is the radial diameter difference divided by the tangent of half the included angle.
What does 90° mean on a countersink? It refers to the included angle of the conical recess, measured across the full cone.
Does a larger countersink angle make the recess deeper? For the same outer and hole diameters, a larger included angle produces a shallower countersink.
Should the countersink diameter be exactly the head diameter? It depends on the required seating condition and manufacturing tolerance. A small allowance may be used when the fastener must sit completely flush.
Does the clearance hole diameter affect countersink depth? Yes. With the same countersink diameter and angle, a larger clearance hole produces a shallower countersink.
Can this be used for CNC machining? Yes, as a geometry calculation aid. The final tool diameter, included angle, depth tolerance and machining process should be checked against the fastener drawing and production requirements.