Calculate counterbore diameter, depth, radial clearance and material-removal dimensions for socket-head and other fasteners.
Radial clearance is the extra space on each side of the fastener head. Recess is the desired distance the head sits below the surrounding surface.
Calculate to see the resulting dimensions.
What is a counterbore? A counterbore is a cylindrical, flat-bottomed recess around a drilled hole that allows a fastener head to sit flush or below the surface.
How do I calculate counterbore diameter? Add twice the desired radial clearance to the fastener head diameter.
How do I calculate counterbore depth? For a flush head, use the fastener head height. If the head must sit below the surface, add the required recess depth.
What is radial clearance? It is the amount of additional space between the fastener head edge and the counterbore wall on one side.
What is diametral clearance? It is the total difference between counterbore diameter and fastener head diameter, equal to twice the radial clearance.
Can the counterbore be larger than the fastener head? Yes. A suitable clearance is normally provided so the head can enter the recess without interference.
Does the clearance hole affect counterbore diameter? The clearance hole determines the inner diameter of the counterbore floor, but the counterbore diameter is primarily determined by the fastener head diameter and required clearance.
Can this be used for CNC machining? Yes, as a geometric calculation aid. The actual counterbore tool diameter, depth tolerance and fastener dimensions should be checked before production.
What is the difference between a counterbore and countersink? A counterbore has straight cylindrical walls and a flat bottom; a countersink has angled conical walls.